***Useful Information For The Working Sparky***

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17TH Edition , Questions & Answers for Examination 2382-10 Requirements for
1. The external influence code ACM requires IP rated equipment to
a. IPX4
b. IPX1
c. IPO
d. IPX2

Electrical Installations



2. AS 7671 is a
a. document designed solely for the use of electricians
I. legal document used in a court of law
c. Bon statutory document
d. statutory document

3. The fundamental principles of BS7671 state that persons and livestock shall be protected against injury as a
consequence of over voltages originating from
a. motors running
I. the operation of circuit breakers
c. atmospheric events
d. voltage recovery

4. The fundamental principles of BS 7671 covering the protection against voltage disturbances etc., states that the
installation shall have an adequate level of immunity against
a. the weather
b. electromagnetic disturbances
c. voltage loss
d. vibration

5. What is the maximum As for a 10A type C circuit breaker protecting a standard discharge type lighting circuit?
a. 1.15 Ohms
I. 2.30Ohms
c. 1.44Ohms
d. 1.92Ohms

6. A double insulated hand held electric drilling machine is known as
a. class II equipment
b. a DeWalt
c. class HI equipment
d. class I equipment

7. An electrical installation certificate should be signed by
a. the local authority
b. a competent person
c. the customer
d. the REC

8. When considering external influences, the code AD4 requires IP rated equipment to
a. IPXO
b. IPX1
c. IPX4
d. IPX5

9. The external influence code AD1 requires IP rated equipment to
a. IPX4
b. IPX1
c. IPXO
d. IPX2

10. When considering external influences, the code AA5 relates to the ambient temperature range
a. -5°C to +45°C
b. -65°C to +5°C
c. +5°C to +40°C
d. -25°C to 0°C


11. When considering external influences, the code AA1 relates to the ambient temperature range
a. -5°C to +45°C
b. -60°C to +5°C
c. +5°C to +40°C
d. -25°C to 0°C

12. Electrical installations shall be divided into circuits to
a. allow easier access to the installation
b. allow more even distribution of power
c. allow for expansion without changing the maximum demand
d. reduce electromagnetic interference

13. One method of determining the external loop impedance is by taking a reading at
a. the origin of supply
b. the supply and furthest outlet
c. the supply and subtracting the values of R1 + R2
d. the furthest outlet from the supply origin

14. The maximum disconnection time for a 230V a.c. final circuit not exceeding 32 amps, with a TT supply is
a. 3s
b. 0.2s
c. 0.5s
d. 5ms

15. The maximum Zs for a 16A Type B circuit breaker protecting a fixed appliance is
a. 1.87 Ohm
b. 0.87Ohm
c. 2.40Ohm
d. 2.87Ohm

16. Undervottage protection is required when the restoration of power may cause
a. accidental RCD tripping
b. unexpected stalling of the motor
c. overload activation
d. unexpected start-up of the machinery

17, A device which cuts off all or part of an installation from every source of electrical energy provides
a. emergency switching
b. isolatior
c. a fireman's switch
d. partial disconnection

18. For a 32A Type B circuit breaker protecting a standard final ring circuit, the maximum Zs would be
a. 0.70 Ohm
b. 0.30 Ohm
c. 1.44 Ohm
d. 0.20 Ohm

19. In a TT installation, distribution circuits must satisfy a disconnection time of
a. 5s

b. 1s
c. 0.6s
d. 0.2s

20. A residual current device (RCD) works by
a. a magnetic device operating in the event of a fault between Live and earth «-> CORRECT ANSWER
b. a magnetic device operating in the event of a fault between neutral and earth
c. a thin element operating in the event of a fault between neutral and earth
d. a thin element operating in the event of a fault between live and earth

21. A RCBO offers protection against
a. short circuit current
b. short circuit and earth fault current
c. short circuit and overload current
d. basic contact

22. Protective measures against electric shock can be achieved by automatic disconnection of the supply and in systems additional protection by means of an red shall be provided for
a. mobile equipment with a current rating exceeding 32 A
b. mobile equipment with a current not exceeding 22 A
c. socket outlets with a rated current exceeding 20 A
d. socket outlets with a rated current not exceeding 20 A
systems additional protection by means of an rcd shall be provided for

23. Protective measures against electric shock can be achieved by automatic disconnection of the supply and in systems additional protection by means of an red shall be provided for
a. socket outlets with a rated current exceeding 20 A
b. socket outlets with a rated current not exceeding 13 A
c. mobile equipment with a current rating not exceeding 32 A
d. mobile equipment with a current rating exceeding 32 A

24. In a.c. systems in the event of the failure of basic protection, additional protection may be provided by
a. supplementary bonding
b. a time delay 100mA RCD
c. an RCD with an operating current not exceeding 30mA
d. electrical separation

25. If a fault occurs in the HV system, and a magnitude of fault voltage of 430 volts occurs between exposed conductive
parts and earth on the LV installation. What is the maximum tolerable duration of the fault?
a. 10 ms
b. 100 ms
c. 200 ms
d. 300 ms

26. If a Line conductor of an IT system is earthed accidentally, the insulation and components rated for the Line to
Neutral voltage can be temporarily stressed with a higher voltage. What value can this stress voltage reach up to?
a. U=V3 U0
b. U=3U0
c. U=V U0
d. U=U0

27. Nuisance tripping from a large transformer installation can be prevented by
a. the use of an RCD
b. the use of a C type MCB
c. the use of a B type MCB
d. the use of a D type MCB

28. In order to reduce the effects of eddy currents when conductors are drawn through a steel conduit system, they
should be arranged so that
a. they are terminated in the correct phase sequence
b. each conductor of an individual circuit takes approximately the same current
c. they are physically separated from the conductors of other circuits within the conduit
d. they are not individually surrounded by the ferrous material -> CORRECT ANSWER

29. If a cable is buried in a wall less than 50mm depth and is not protected by metallic enclosures, the additional
protection required is
a. RCD protection -
b. MCB protection
c. supplementary bonding
d. external notification of cable routes

30. At which one of the following terminations would a warning notice NOT need to be attached
a. a copper water pipe
b. a bonded gas pipe
c. an earthing terminal within a consumer unit
d. an earth electrode

31. When determining design current, the correction factor that is applied to a BS3036 rewirable fuse is
a. 0.752
b. 0.527
c. 0.725
d. 1.725

32. A BS1361 protective device is also known as a
a. circuit breaker
b. cartridge fuse
c. RCD
d. semi enclosed rewirable fuse

33. An installation protected by an RCD shall have a fixed notice stating
a. the test button should be pressed occasionally
b. the test button should be pressed monthly
c. the test button should be pressed quarterly
d. the test button should be pressed at 6 monthly intervals

34. When insulated a PEN conductor shall be identified with
a. blue insulation along its length
b. green insulation and blue markings at the termination
c. green and yellow insulation and blue markings at the termination
d. green and yellow insulation along its length

35. Outdoor lighting does NOT involve
a. shelters
b. festoon lighting
c. road trafic signals
d. floodlighting

36. Where it is necessary to install cables within a wall consisting of a metal construction, the circuit should
a. adequately bond the studwork
b. be RCD protected
c. be MCB protected
d. be sheathed in metallic conduit

37. Where it is necessary to limit the consequences of the risk of fire due to fault currents, an RCD
a. shall be installed at the end of the circuit to be protected

 

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b. shall be installed at the origin of the circuit to be protected
c. is used to switch off the line conductor in the event of a faun
d. is used to switch off the neutral conductor in the event of a fault

38. In Great Britain the use of Combined protective and neutral (PEN) conductors is prohibited in consumers installations by which regulations?
a. The Electricity at Work Regulations 1989
b. The Supply of Machinery (Safety) Regulations 1992
c. The IEE Wiring Regulations
d. The Electricity Safety, Quality and Continuity Regulations 2002

39. In Great Britain the use of Combined protective and neutral (PEN) conductors is prohibited in consumers installations. One of the exceptions from this is
a. where the supply is feeding an agricultural installation
b. where the installation is supplied by a privately owned transformer which has a metallic connection with the distributors
network
c. where the supply is obtained from a private generating plant
d. where the supply is feeding a swimming pool

40. Where a generating set is used as an additional source of supply in parallel with other sources, it shall be instated
a. on the supply side of all the protective devices for the final circuits of the installation with a number of additional
requirements
b. on the supply side of all the protective devices for the final circuits of the installation with no additional requirements ~>
c. on the load side of all the protective devices for the final circuits of the installation with no additional requirements
d. on the load side of all the protective devices to the final circuit which must be connected by plug and socket

41. Regarding auxiliary supplies to safety services, the maximum changeover time refers to
a. how long the safety source can supply the rated power output to the safety service
b. the frequency (in cycles per second) of the auxiliary supply feeding the safety service
c. how often maintenance has to be carried out on the auxiliary supply
d. the time It takes for the safety source to supply the power to the safety service, after the loss of the main power supply

42. The minimum value of insulation resistance test performed on a PELV installation is
a. 10.0 MOhm
b. 2.0 MOhm
c. 0.3 MOhm
d. 0.5 MOhm

43. The minumum value of insulation resistance test performed on a SELV installation is
a. 99.0 MOhm
b. 2.0 MOhm
c. 0.3 MOhm
d. 0.5 MOhm

44. During the initial verification of an installation, which of the following forms part of the checklist?
a. maximum demand and diversity
b. Design briefs
c. contractors notes
d. presence of diagrams and instructions

45. An earth fault loop impedance test performed on a final ring circuit will record
a. the external loop impedance
b. the resistance of the line and protective conductors and external loop impedance
c. the resistance of the line and protective conductors
d. the protective conductor resistance

46. A polarity test would be conducted to verify
a. every fuse and single pole device is connected in the line conductor only -
b. there is sufficiently low resistance to operate the protective device within its limits
c. there is sufficient circuit protection
d. there is no breakdown of the conductor insulation

47. The minimum value of insulation resistance of a PELV circuit is
a. 0.5 MOhm
b. 1MOhm
c. 1.5 MOhm
d. 5MOhm

48. Within an agricultural installation, bonding conductors can be
a. 6.0mm2 aluminium conductors
b. 4.0mm2 aluminium conductors
c. 4.0mm2 copper conductors
d. 5.0mm2 copper conductors

49. Self supported suspension cables within agricultural situations should be
a. at a height of a least 2m
b. at a height of a least 4m
c. at a height of a least 6m
d. at a height of a least 10m

50. If SELV or PELV is used within agricultural premises, barriers or enclosures must conform to at least
a. IP4X
b. IPXXB
c. IPX4
d. IP67

51. Within zone 2 of an outdoor swimming baths where no water jets are used, installed electrical equipment should be rated
a. IPX4
b. IP2X
c. IPXXB
d. 1PX8

52. In an area containing a bath or a shower, socket outlets must be installed
a. 3m horizontally from zone 1
b. 3m horizontally from zone 0
c. 3m horizontally from zone 2
d. within zone 2 but outside zone 1

53. Where contact with skin or footwear is likely, the floor temperature of an underfloor heating installation should be limited to
a. 20°C
b. 35°C •
c. 40°C
d. 70°C


54. A mobile unit should have a connection between the
a. live and neutral
b. neutral and earth
c. vehicle chassis and main bonding terminal
d. battery terminals and supply

55. On the d.c. side of a PV power supply system, the type of insulation that is preferable is
a. Class II-
b. Class I
C XLPE

d. 1000v VDS

56. In marina installations that are NOT in an area subject to vehicle movement, overhead distribution cables shaft be installed at a height of
a. 5.5m
b. 4.5m
c. 6.5m
d. 3.5m

57. In areas that are not subject to vehicle movement on a caravan site, overhead distribution cables shall be installed at a heigth of
a. 6m
b. 3.5m
c. 5m
d. 10m



58. BS 6004 relates to
a. emergency lighting
b. electrical cables
c. 13A plug cartridge fuses
d. RCDs

59. BS 5266 relates to
a. emergency lighting -
b. electrical cables
c. 13A plug cartridge fuses
d. 13A plugs

60. The correction factor for three multicore cables installed in single layer fashion on a wail is
a. 0.75
b. 0.85
c. 0.79
d. 0.99


ANSWERS

1-a 2-c 3-c 4-b 5-b 6-a 7-b 8-c 9-c 10-c 11-b 12-d 13-a 14-b 15-d 16-d 17-b 18-c 19-b

20-a 21-b 22-d 23-c 24-c 25-d 26-a 27-d 28-d 29-a 30-c 31-c 32-b 33-c 34-c 35-b 36-b

37-b 38-d 39-c 40-b 41-d 42-d 43-d 44-d 45-b 46-a 47-a 48-c 49-c 50-b 51-a 52-a 53-b

54-c 55-a 56-d 57-b 58-b 59-a 60-c
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17th Edition stuff , Part 4 -
Protection for Safety :

Part 4 is reorganised with subject matter more closely grouped eg basic requirements and application requirements are now in the same chapter.
Part 4 has also a number of important changes.
Protection against direct contact has been replaced by “basic protection” which is defined as:- protection against electric shock under fault free conditions.
Protection against indirect contact has been replaced by “fault protection” which is defined as:- protection against electric shock under single fault conditions.
EEBADS is now an out of date term referring only to fault protection measures and this is now replaced by ADS:- Automatic Disconnection of Supply, which is a protective measure including both basic and fault protection.
Table 41A – Maximum disconnection times, has been extended and modified. Now replaced by table 41.1 this new table includes final TN and for the first time TT circuits. Disconnection times for circuits not exceeding 32A are tabulated for a range of ac and dc nominal line voltages
E.g.:
for a 230V I6A TN circuit t = 0.4s
for a 230V 16A TT circuit t = 0.2s
for final circuits exceeding 32A:- for a 230V TN circuit, t = 5s : max for a 230V TT circuit t = 1s max :

The terms fixed and non fixed equipment have been removed and no longer apply e.g. for previous fixed equipment in a TN circuit the value of 5s no longer applies and is now covered in table 41.1 as 0.4s or for circuits exceeding 32A, 5s.
As well as maximum disconnection times for TT systems being introduced into BS 7671 where an RCD is used for earth fault protection in a TT system an additional condition must be met. This is that RA x I∆n ≤ 50V (section 411.5.3).

 

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2392-10 : just off the press this is the New Sh—there hitting you with ,


(42) Prospective Short Circuit Current is Measured at the Supply with the Main Earthing Conductor :
(a) Connected to the Main Earth Terminal :
(b) Connected to the Neutral Supply :
(c) Disconnected from the Main Earth Terminal : *****
(d) Connected to the Line Supply :

Measurement of Prospective Short Circuit Current :
CCU :
Note : the Neutral & Earth Probes are Connected to the Natural Terminal ( Line by is self )
Note : Not on the ( MET ) Main Earthing Terminal ( Earth Connection Block :

(41) Prospective Earth Fault Current ( PEFC ) is Measured between :
(a) Line & Neutral :
(b) Line & Earth : *****
(c) Neutral & Earth :
(d) R1 & R2
Measurement of Prospective Earth Fault Current :
CCU :
Note : the Neutral Probe (N) Only : the Line Probe ( L ) Only :
Note : Earth Probe : on the ( Earth Connection Block : ( MET )

(40) Prospective Short Circuit Current ( PSCC ) is Measured between :
(a) Line & Neutral : *****
(b) Line & Earth :
(c) Neutral & Earth :
(d) R1 & R2

(0)Measurement of External Loop Impedance : ( Ze )
CCU :
Note : the main Earth is Disconnected from main bonding conductors and Circuit Protective conductors for this Test ,
Note : Main Switch in “ OFF “ Position :
Note : the Neutral Probe (N) Only : the Line Probe ( L ) Only :
Note : Earth Disconnected from the ( MET ) Main Earthing Terminal

(37) RCD tests should include :
(a) Half times /no trip , 1 times 40mS , 5 times / 0.45 ,
(b) Half times / 40mS , I times no trip , 5 times / 300ms ,
(c) Half times / no trip , I times 300mS , 5 times / 40mS **** ( am basing them on BS-EN - )
(d) Half times / 0.45 , I times 30mS , 5 times / 300mS ,

(31) When checking Polarity with test probes the voltage indication on a single phase socket outlet should be :
(a) L-N 230V , L-E 230V , N-E , 230V
(b) L-N 230V , L-E 0V , N-E , 230V
(c) L-N 0V , L-E 230V , N-E , 0V ,
(d) L-N 230V , L-E 230V , N-E , 0V , *****

( 47) An Electrical Installation Certificate consists of : ( Remember this One a Must ) ↔↔↔↔↔↔↔↔↔↔↔↔↔
(a) A two page Certificate :
(b) A two page Certificate and Schedule of Inspections :
(c) A two page Certificate and Schedule of Test Results :
(d) A two page Certificate, A Schedule of Inspections and a Schedule of Test Results :

(48) The Electrical Certificate required to be completed for a domestic shower circuit would be : ( Remember this One a Must ) ↔↔↔
(a) A Minor Works Electrical Installation Certificate :
(b) A Minor Works Electrical Installation Certificate and a Schedule of Test Results :
(c) A Minor Works Electrical Installation Certificate and a Schedule of Inspections and a Schedule of Test Results : *****
(d) No Certification Required :

( 47) ( D ) Ops

(49) Volt drop in a cable will :
(a) Increase with Increase in Length : *****
(b) Decrease with increase in Length :
(c) Not affected by increase in Length :
(d) Increase with a reduction in length :

(44) Voltage drop can be evaluated by using which one of the following test values :
(a) External Loop Impedance (Ze ) :
(b) Final Circuit earth Fault loop Impedance (Zs ) : *****
(c) Insulation Résistance :
(d) RCD tripping times :

2392-10 : Certificate in Fundamental Inspection and Initial Verification of Electrical Installations

(1) An initial verification is carried out to ensure that :
(a) All fixed equipment , parts and material are erected correctly to British Standards : *****
(b) No claim can be made for poor workmanship :
(c) A certificate is issued to the tenant of the property :
(d) The building insurance policy cast is kept to a minimum :

(2) Three items of information required for the initial inspection are :
(a) Maximum demand , type of earthing and supply characteristics : *****
(b) Cost of work, time taken and number of electricians :
(c) Serial number of instrument , schedule of test results , order number :
(d) Estimated time , start time and total hours taken :

(3) Three statutory and non statutory most relevant guidance materials for initial verification :
(a) COSHH regs , CDM regs , and PUWER regs , :
(b) Working at Height regs , and Working in Confined Spaces Act :
(c) Health and Safety Policy , Liability insurance and building insurance :
(d) EAWR 1989 , BS-7671:2008 , and IEE guidance notes 3 : *****

(4) Three locations and associated equipment requiring specific guidance material would be :
(a) Bedroom ,Lounge and Garage :
(b) Roofs , Cellars and Lofts :
(c) Explosive atmospheres , combustible dust and open cast mines : ( Mac two Answers on sheet C / D ) ???????? Help
(d) Offices , workrooms and classrooms :

(5) Some of the essential and optional information required on the Electrical Installation Certificate and Minor Electrical Installation Work Certificate is :
(a) Number of rooms , type of lighting , outdoor supplies :
(b) Floor area , separate building , number of floors ,
(c) Means of earthing , main protective conductors and supply characteristics : *****
(d) Name of sub-contractor , invoice , contact number :

(6) Two human senses that may be employed during the initial verification are :
(a) Thought and speech :
(b) Movement and pain :
(c) Gut feeling and taste :
(d) Sight and touch : *****

(7) Two main items to be checked for given systems and locations are :
(a) Light levels and stroboscopic effect :
(b) Number of appliance and Pat test labelling :
(c) Connection of conductors and cable selection : *****
(d) Empty premises or tenanted :

(8) Two requirements of the EAWR 1989 for safe inspection and testing are :
(a) Excess current protection and means of isolation : *****
(b) Two inspectors are required and one person under supervision :
(c) Presence of tenant and building inspector during verification :
(d) Spare instrument batteries and spare test leads :

(9) Instruments should be in accordance with :
(a) HSG 141 ,
(b) GS-38 , *****
(c) BS-7671 ,
(d) IEE Guidance Note 3 ,

(10) The correct Instruments or settings required to carry out domestic installation testing are ,
(a) Multimeter , Ammeter , Voltmeter and Watt meter ,
(b) Low insulation tester , light meter , power meter ,
(c) Pipe locator , cable finder , fuse checker and buzzer ,
(d) Continuity , insulation , loop impedance and RCD , ***** GN-3

(11) The first three tests to carry out on an initial verification are :
(a) Verification of switch operation , fuse test and lamp test ,
(b) Continuity of protective conductors , continuity of ring and insulation résistance , ***** GN-3
(c) Verification of voltage drop , functional testing of polarity ,
(d) Electrical separation , earth electrode test and phase sequence ,

(12) The four earthing arrangements in a domestic installation are ,
(a) Cross bond , main earth , earth electrode and supply cable earth ,
(b) Protective conductors in lighting , socket outlets , cooker and shower ,
(c) Bonding conductors to Gas , Water , Central heating and kitchen sink ,
(d) Main earth , main bonding , circuit protective conductors and supplementary bonding , *****

(13) Continuity of protective conductors gives a reading of ,
(a) R1 + Rn ,
(b) Ze + Zs ,
(c) R1 + R2 , ***** ( remember they are not asking you about little r1 + r2 , End to End
(d) r1 + r2 ,

(14) Increasing conductor length and decreasing conductor cross sectional area , ( CSA )
(a) Increases résistance , ***** Remember this one ,
(b) Decreases résistance ,
(c) Has no effect on résistance ,
(d) Causes the résistance value to remain the same due to both changes ,

(15) An increase in ambient temperature would cause the résistance of a conductor to ,
(a) Increase ,
(b) Decrease ,
(c) Vary ,
(d) Remain the same ,

(16) Connecting conductors’ in parallel would ,
(a) Reduce the overall value of résistance , *****
(b) Have no effect on the résistance compared to one conductor ,
(c) Double the résistance value of résistance ,
(d) Increase the overall value of résistance ,

(17) On a ring continuity test (R1 + R2 ) can be calculated by ,
(a) Adding line ( r1 ) and protective conductor ( r2 ) ,
(b) Subtracting ( r2 ) from ( r1 ) ,
(c) Adding ( r1 ) to ( r2 ) and dividing by ( 4 ) , **** ( Remember this if your doing your 2391-10 ) look back on these pages , it all there ,
(d) Adding ( r1 ) to ( r2 ) and multiplying by ( 4 ) ,

(18) Decreasing a conductor length with cause its résistance to ,
(a) Remain the same ,
(b) Vary ,
(c) Increase ,
(d) Decrease , *****

(19) Where cables are connected in parallel the overall insulation résistance ,
(a) Stay the same .
(b) Varies ,
(c) Increase ,
(d) Decreases ,

(20) Insulation résistance is measured in ,
(a) mΩ
(b) Ω
(c) KΩ
(d) MΩ

(21) Before carrying out an insulation résistance test consideration must be given to ,
(a) Client consultation , safety procedures and notices , *****
(b) Checking the results and verifying them ,
(c) The supply voltage and frequency ,
(d) Ze and PFC ,

(22) Before carrying out an insulation résistance test ,
(a) Carry out verification of voltage drop ,
(b) Ensure supply is switched on ,
(c) Contact local authority building control ,
(d) Safely isolate and consider electronic components and voltage sensitive equipment , *****

(23) When carrying out an insulation résistance test , tests should be between ,
(a) Live to Neutral and Live to Earth , ( Mac two Answers on sheet A / B ) ???????? Help ( Myself ( A ) Tutors for you ?
(b) Live to Live and Live to Earth ,
(c) Earth to Neutral and Earth to Earth ,
(d) Neutral to Neutral and Live to Earth ,

( A low resistance between phase and neutral conductors, or from live conductors to earth, will result in a leakage current. )

 

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(24) The required test voltage and minimum value of résistance for circuit above 50V to 500V is :
(a) 250v / 0.5mΩ ,
(b) 500v / 1MΩ , *****
(c) 250v / 1MΩ ,
(d) 500v / 0.5MΩ ,

(25) The insulation résistance test to verify separation between SELV circuits and other circuits should be ,
(a) 250v / 0.5mΩ ( table 61 regs ) *****
(b) 500v / 1MΩ
(c) 250v / 1MΩ
(d) 500v / 0.5MΩ

(26) A shower located in a room above a bath would be : ( regs 701.512.2 (ii ) in zone 1 – 2 : IPX4 , lighting bathroom ,
(a) In zone 0 , IP4X and not RCD protected ,
(b) In zone 1 , IPX4 and RCD protected , *****
(c) In zone 2 , IPX8 and not RCD protected ,
(d) In zone 0 , IPX8 and RCD protected ,
( anything that moves in bathroom RCD it 30mA ) 17th Edition ,
( Zone 1 : IPX4 , Zone 0 : IPX7 , Zone 2 : IPX4 , Electrical equipment exposed to water jets , e.g. IPX5 : ←←←

(27) The appropriate IP code for finger protection from contact with a Live terminal is ,
(a) IP2X , ***** ( how to remember Two Finger up , V )
(b) IP4X ,
(c) IPX2 ,
(d) IPX4 ,

(28) A polarity test is carried out to confirm ,
(a) RCD is in the Live side of the circuit ,
(b) Main double pole switch is in the Live side of the circuit ,
(c) Single pole switches , cable contact of Edison screw lampholders and fuses are in the Live side of the circuit , *****
(d) Double pole switches are in the Live side of the circuit ,

(29) Correct polarity of a final circuit can be confirmed during the ,
(a) Protective conductor continuity test ( R1 + R2 ) , *****
(b) Insulation résistance test ,
(c) External loop impedance test ,
(d) Protective fault current test ,

(30) Correct polarity is confirmed when supply is switched on to confirm ,
(a) Correct polarity of final circuit ,
(b) Correct polarity of final circuit and supply connections , *****
(c) Correct polarity of supply connections ,
(d) Correct polarity of portable equipment ,

(32 ) Earth electrodes’ can be tested using ,
(a) A voltmeter or ammeter ,
(b) A Insulation résistance tester or continuity tester ,
(c) An earth electrode or loop impedance tester , ***** ( Remember 2 Instrument’s Used , method 1 , method 2 , )
(d) An RCD tester or frequency meter ,

(33) When measuring earth electrodes’ using an earth fault loop impedance tester the tester should be connected ,
(a) To the furthest point ,
(b) To every socket outlet of the ring in turn ,
(c) To the installation supply with the main earthing conductor disconnected from the main earthing terminal , *****
(d) At mid point in a ring circuit ,

(34) A supply earthing arrangement which has a combined neutral and earth is a ,
(a) TN-S- system ,
(b) TN-C-S - system , ***** ( Look up in the regs , Definitions , p-33 )
(c) TT- system ,
(d) IT- system ,

(35) Earth fault loop impedance values for ( Zs ) is carried out ,
(a) At the supply ,
(b) At the first socket in a ring circuit and furthest lighting point in a lighting circuit ,
(c) At all consumer unit MCB outgoing terminals ,
(d) At all sockets in a ring circuit and furthest lighting point in a lighting circuit , *****

(36) A measured value of ( Zs ) can be compared with the maximum tabulated value by 0.8 ,
(a) Multiplying the tabulated value by 0.8 , ↔ ( Mac I could be wrong here I’ll stick my neck out ) Help !!!!!! A / D
(b) Multiplying the measured value by 0.8 ,
(c) Dividing the tabulated value by 0.8 ,
(d) Dividing the measured value by 0.8 ,

Ambient temperature at the time of test , and the maximum conductor operating temperature , both of which will have an effect
On conductor résistance , hence , the ( R1 + R2 ) could be greater at the time of fault than at the time of test ,
Our measured value of ( Zs ) must be corrected to allow for these possible increases in temperature occurring at a later date , this
Requires actually measuring the ambient temperature and applying factors in a formula ,
( which simply requires that the measured value of ( Zs ) does not exceed 0.8 of the appropriate tabulated value gives the 0.8 values of the tabulated loop impedance for direct comparison with measured values )
In effect , a loop impedance test places a Line / Earth Fault on the Installation ,
The value of ( Zs ) will have to be determined from measured values of ( Ze ) and ( R1 + R2 ) and the 0.8 rule applied ,

Note : Never Short out an RCD in Order to conduct this Test :
As a Loop Impedance test creates a high Earth Fault Current , albeit for a Short Space of time , some lower rated circuit breakers may operate , resulting in the same situation as with an RCD , and ( Zs )
Earth Fault Loop Path : Fault current , Exposed Conductive Path , TN-C-S ( Ze – 0.35Ω pen conductor ) TN-S ( Ze – 0.8Ω )

External Loop Impedance ( Ze )
The value of ( Ze ) is measured at the intake position on the supply side , and with all main protective bonding disconnected ,
Unless the Installation can be isolated from the supply , this test should not be carried out ,
As a potential shock risk will exist with the supply on and the main protective bonding disconnected ,

Additional protection RCD / RCBO operation :
Where RCDs / RCBOs are fitted it is essential they operate within set parameters , The RCD testers used are designed to do just this ,
Basic tests required are as follows :
(1) Set the Instrument to the rating of the RCD :
(2) Set the Instrument to half-rated trip :
(3) Operate the Instrument and the RCD , should “ Not trip “
(4) Set the Instrument to deliver the full rated tripping current of the RCD , ( I∆n )
(5) Operate the Instrument and the RCD , should trip out in the required time :
(6) For RCDs rated at 30mA or less set the Instrument to deliver ( x5 ) times the ratted current of the RCD , ( 5 I∆n )
(7) Operate the Instrument and the RCD , should trip out in ( 40mS )

( PS , I wont give up my day job )

(38) RCDs can be used for ,
(a) Overload protection of portable appliances ,
(b) Additional protection of socket outlets up to 20A , special locations’ and installations , *****
(c) Fault current protection of equipment and socket outlets rated above 32A
(d) Basic protection ,

(39) RCDs connected in series must have ,
(a) Delay operation facilities ,
(b) Indicator lamps of different colours ,
(c) One combined test button facility ,
(d) Discrimination between RCDs , *****

(43) Prospective fault current measurement ensures that ,
(a) Cables can carry the required load current ,
(b) The consumer unit main switch can be operated during a fault ,
(c) The over current protective devices at that point in the installation can disconnect the fault current , *****
(d) The main fuse will operate in the event of a fault ,

(45) The maximum permitted voltage drop to BS-7671:2008 for ,
(a) 4% lighting 4% other uses ,
(b) 9.2% lighting 4% other uses ,
(c) 2.5% lighting 4% other uses ,
(d) 3% lighting 5% other uses , ( Appendix 12 , p-358 ) *****

(46) The requirements for erection of electrical installations are given in ,
(a) Electricity at Work Regulations 1989 ,
(b) IEE On Site Guide ,
(c) Building Regulations ,
(d) BS-7671 :2008 , ***** ( regs chapter 52 : P-97 )

(50) Instruments used for electrical installation testing should be ,
(a) Calibrated on a regular basis , *****
(b) Exempt from calibration ,
(c) Calibrated after and initial verification ,
(d) When the batteries are dead ,

State the Recommended Sequence of Tests Covered by this Unit and the Reasons for that Sequence :

Sequence taken from BS-7671 : 2008 Part 6

………………….. Test …………………………………………….. Reason ………..
Continuity of protective conductors : R1 + R2 value , Metalwork & Effective IR testing
Continuity of Ring Final Circuit : R1 + R2 value , No Interconnected ring
Insulation Résistance : No Short-between Line , Neutral & Earth
SELV : No Connection between Low & Extra Low-Circuits
PELV No Connection between Low & Extra Low-Circuits
Electrical Separation : No Connection between Low & Extra Low-Circuits
Basic protection by barrier or Enclosure : No finger or other solid more than 1mm
Insulation / Impedance of Floors and Walls : Effectiveness of high Résistance / Impedance Location
Polarity : Switches , Fuses , breakers etc in live side of circuit
Earth Electrode Résistance : Resistive Contact of Electrode to Ground :
Earth Fault Loop Impedance : To meet final circuit disconnection time in event of fault :
Additional protection / RCD test : To ensue RCD operates in time in event of Fault or misuse :
Prospective Fault Current : To ensue protective devices can disconnect fault effectively :
Check of Phase Sequence : To ensue 3 Phase motors etc, rotate incorrect direction :
Functional Testing : To Test RCD test button , Switches , breakers , locks etc, operate
Verification of Volt Drop : To ensue voltage at load end is within required limits ,

 

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Insulation Resistance Testing: How and Why ? Our cousins Overseas : IEE :

How significant is insulation resistance testing ? Since 80% of electrical maintenance and testing involves evaluating insulation integrity, the answer is "very important." Electrical insulation starts to age as soon as it's made. And, aging deteriorates its performance. Harsh installation environments, especially those with temperature extremes and/or chemical contamination, cause further deterioration. As a result, personnel safety and power reliability can suffer. Obviously, it's important to identify this deterioration as quickly as possible so you can take the necessary corrective measures.
What is insulation resistance testing? Basically, you're applying a voltage (specifically a highly regulated, stabilized DC voltage) across a dielectric, measuring the amount of current flowing through that dielectric, and then calculating (using Ohm's Law) a resistance measurement. Let's clarify our use of the term "current." We're talking about leakage current. The resistance measurement is in megohms. You use this resistance measurement to evaluate insulation integrity.
Current flow through a dielectric may seem somewhat contradictory, but remember, no electrical insulation is perfect. So, some current will flow.
What's the purpose of insulation resistance testing? You can use it as:
• A quality control measure at the time a piece of electrical equipment is produced;
• An installation requirement to help ensure specifications are met and to verify proper hook up;
• A periodic preventive maintenance task; and
• A troubleshooting tool.
How do you perform an insulation resistance test? Generally, you connect two leads (positive and negative) across an insulation barrier. A third lead, which connects to a guard terminal, may or may not be available with your tester. If it is, you may or may not have to use it. This guard terminal acts as a shunt to remove the connected element from the measurement. In other words, it allows you to be selective in evaluating certain specific components in a large piece of electrical equipment.
Obviously, it's a good idea to have a basic familiarity with the item you're testing. Basically, you should know what is supposed to be insulated from what. The equipment you're testing will determine how you hook up your meghommeter.
After you make your connections, you apply the test voltage for 1 min. (This is a standard industry parameter that allows you to make relatively accurate comparisons of readings from past tests done by other technicians.)
During this interval, the resistance reading should drop or remain relatively steady. Larger insulation systems will show a steady decrease; smaller systems will remain steady because the capacitive and absorption currents drop to zero faster than on larger systems. After 1 min, you should read and record the resistance value.
When performing insulation resistance testing, you must maintain consistency. Why? Because electrical insulation will exhibit dynamic behaviour during the course of your test; whether the dielectric is "good" or "bad." To evaluate a number of test results on the same piece of equipment, you have to conduct the test the same way and under the relatively same environmental parameters, each and every time.
Your resistance measurement readings will also change with time. This is because electrical insulation materials exhibit capacitance and will charge during the course of the test. This can be somewhat frustrating to a novice. However, it becomes a useful tool to a seasoned technician.
As you gain more skills, you'll become familiar with this behaviour and be able to make maximum use of it in evaluating your test results. This is one factor that generates the continued popularity of analogue testers.
What affects insulation resistance readings? Insulation resistance is temperature-sensitive. When temperature increases, insulation resistance decreases, and vice versa. A common rule of thumb is insulation resistance changes by a factor of two for each 10 DegrC change. So, to compare new readings with previous ones, you'll have to correct your readings to some base temperature. For example, suppose you measured 100 megohms with an insulation temperature of 30 DegrC. A corrected measurement at 20 DegrC would be 200 megohms (100 megohms times two).
Also, "acceptable" values of insulation resistance depend upon the equipment you're testing. Historically, many field electricians use the somewhat arbitrary standard of 1 megohm per kV. The international Electrical Testing Association (NETA) specification Maintenance Testing Specifications for Electrical Power Distribution Equipment and Systems provides much more realistic and useful values.
Remember, compare your test readings with others taken on similar equipment.

The 17th Edition :

Limits this to : ( regs p-358 )
Voltage drop in Consumer’s Installations ,
The Voltage drop between the origin of an Installation and any load point should not be greater than the values in table 12A
Expressed with respect to the value of the nominal voltage of the Installation ,
The calculated Voltage drop should include any effect due to harmonic currents :

3% for lighting ,
5% for Other Uses ,
3% of 230 = 6.9v
3 x 230 ÷ 100 = 6.9v
5% of 230v = 11.5v
5 x 230 ÷ 100 = 11.5v

6% & 8% respectively are permitted for private supplies ,

Ring Final Circuit : GN-3 ( Dead Test ) 2392-10
Instrument : Set : on Ohms –

Under : “ Schedule of Test Results “ Circuit Loop Impedance Ω : ( Ring Final Circuits , Only Measured End to End ,

Line / Line : Little : r1 = 0.43Ω ( Measured End to End ) ↔ Big Copper Lower Résistance )
Neutral / Neutral : Little : r n = 0.42Ω ( Measured End to End ) ↔ Big Copper Lower Résistance )
Earth – Earth : Little : r2 = 0.73Ω ( Measured End to End ) ↔ Smaller C.S.A. ↔ High Résistance )

The Three Test Results can know be put Onto the “ Test Result Sheet “

Domestic Electrical Installation Certificate : “ Test Results “ > Circuit Impedance ( Ω ) :
( Ring Final Circuit(s) Only / Measured End–to–End , > Test Results in Box <

“ Résistance and the Conductor “ 2392-10

Résistance is directly proportional to Length and inversely proportional to “ C.S.A” simply this means that More Length > More Résistance ,
and Less Length > Less Résistance , Also the Greater the C.S.A. the Less the Résistance , and the Smaller the C.S.A. the Greater the Résistance

The Circuit Design why ? : Apprentices

Lighting circuits are almost always wired in Parallel - from strings of Christmas tree lights to the lights in your home - since adding another light to the parallel circuit does not affect the voltage reaching the lights already in the circuit. If for example you were to wire two 12V bulbs in series with a 12V battery, each bulb would receive only 6 Volts. Wired in Parallel each bulb still receives the 12 Volts it needs. Also, if one bulb fails, the rest of the bulbs will remain lit ,

Circuit Résistance in Parallel

Résistance is directly proportional to length and inversely proportional to c.s.a. Simply this means that more length, more Résistance, and less length less Résistance. Also the greater the c.s.a. the less the Résistance, and the smaller the c.s.a. the greater the Résistance.

 

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Amberleaf ( 6 – Pack Tonight )

Passed My 2392-10 Certificate / Fundamental Inspection , Testing & Initial Verification :

Have a lot off 2391-10 stuff , when I get a chance I’ll down load them ,

Jason I’ll need to use a new folder Amberleaf , how will I word it !!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Testing –

The Obtaining and Recording of the Installations ( Psc ) & ( Ze ) Details :

When Obtaining the Values of either the Psc & Ze at the Origin of the Installation three Methods appear to be Acceptable :

(1) By Enquiry : Usually given upon request to the local Regional Electricity Board , it is common practice for them to quote
A maximum value “ this usually being 16kA for the Prospective Short Circuit Current and earth loop values of 0.35Ω for TN-C-S 0.8Ω for a TN-S system , O.S.G. p-11

(2) By Calculation :
The Designer , using information given , with regard to cable sizing , length of run from the sub-station , etc , can calculate the (PSC ) & the Phase Earth Loop Impedance at the Origin of the Installation ,

(3) By Direct Measurement :
Using a Instrument a direct measurement can be made for the ( PSCC ) ↔ ( PFC ) & ( Ze ) of the Installation
at the Supply intake Terminals ,

* Test results do not specify whether the actual recorded instrument reading is that of a ( Phase / Neutral or a ( Phase / Phase short circuit ,
Although the worst scenario is a short circuit fault across the three phase it appears that a Phase / Neutral measurement is acceptable :

“ Measurement of the Prospective Earth Fault Current “
To measure the Earth Fault Current as a direct reading in Amps , the Instrument ( Neutral Lead can be Connected to the Earth Block )
with the Instrument still set on the current range what will now be measured is the Prospective Earth Fault Current ,

* ( Psc ) range kA ,
By Using this method it saves you having to divide the Earth Loop Impedance reading previously obtained into the supply voltage to
obtain the Earth Fault Current ,
Prospective Short Circuit Current to be measured and recorded , but where the Prospective Earth Fault Current exceeds that of the Short Circuit Current then this Value should be recorded in its place ,
the value of whichever is the Greater should be recorded on the Certificate as the Prospective Fault Current ( Pfc )

“ Measurement of the Short Circuit Current “
“ Range kA “
The test is made using a dedicated ( Psc ) Instrument connected as ( Line & Neutral )
( Most Earth Loop Impedance Instruments incorporate the facility for the measurement of the Phase-Neutral Prospective Short Circuit Current ,

The Protective Devices at the Point of Test must have a Short Circuit Rating in Excess of the reading taken ,
( the Exemptions from this Requirement are when MCBs etc. are used for Overload Protection and BS-1361 or BS-88
Protective devices with suitable operating Characteristics { POSITIONED on the SUPPLY SIDE ϟϟ }

Contractors will Only have Instruments capable of Psc measurement’s at 230V , so a problem will arise on Three Phase systems where a
Ph – Ph –Ph measurement is required , if a 3-Phase measurement is required it has unfortunately become common practice to multiply
The Single Phase recorded measurement by a factor of ( Ѷ 3 )
On Three Phase systems it should be policy to measure and record both the Three Phase Short Circuit Current ( Ph-Ph-Ph ) and
Single Phase Short Circuit Fault Current ,
( Unfortunately Obtaining the ( Ph-Ph-Ph ) Short Circuit Current is easier said than done ,

The Earth Fault Loop Impedance ( Zs ) is made up of the Impedance of the Consumers Phase & Protective Conductors ( R1 and R2 )
Respectively , and the Impedance external to the Installation ( Ze ) Impedance of the Supply ,
As the value of ( Ze ) will be obtained from the Electricity Company for the Initial assessment of the Installation ,
The maximum Impedance allowed for the Phase & Protective Conductors can be determined from :
( Zs + Ze + R1 + R2 )

Radial Circuit :
13Amp Immersion heater circuit protected by a Type B 16amp MCB , wired in 2.5mm2 PVC sheathed cable with a 1.5mm2 CPC
Supplied from 230 volt single phase TN-C-S system , what is the maximum length of run ? ( mV 19.51 x A 16 = 31.2m ) 2391 **

If = Uo / Zs : ( 230v Phase to Earth ) 230 ÷ 0.93Ω = 247A

Zs : R1 , 0.5Ω + R2 , 0.43Ω = 0.93Ω

 

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2392-10 Domestic Electrician’s ←←←←←←←←

-&- are asking for : ( Calculating of R1+R2 ) Calculating of MΩ in parallel , look back through the pages , Ps : Earth Electrode Calculating I got 9 off the this , BE AWARE ↔↔↔↔↔↔↔↔↔↔ Ambeleaf

 

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2392-10

i) Prospective Short Circuit Current is due to a Fault between Phases on Phase and Neutral :
ii) Prospective Earth Fault Current is due to a Fault between Phase and Earth :

i) Prospective Fault Current : intake position – house , ( PFC = 230 ÷ 0.2 = 1150.A / 1.15kA :
ii) Prospective Fault Current : complex “ Dist , Board “ ( PFC = 230 ÷ 0.46 = 500A / 0.5 kA :

Remember to look through your Cals on the pages , its your Butt on the Line , 2392-10 ←←←
You need to think like a Tester ,

 

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Visual Inspection 0nly :

Until an obvious fault develops, most householders appear to assume that their electrical installations are
safe, and will remain so forever. Even those who appreciate that electrical installations eventually need
to be checked appear reluctant to pay for a full BS-7671-style periodic inspection, except perhaps when
they are buying or selling a property. Therefore, even given the significant limitations of ‘visual inspection
only’ such inspection by a competent person can usefully serve to identify damage, deterioration and, to
some extent, defects, which might otherwise go unnoticed by those using the installations.

in principle, visual inspection of the electrical installation in a dwelling by a competent person is an important part of the assessment of the condition of that installation. Visual inspection can identify damage, deterioration and
some defects in installations. Given the potential benefits, the NICEIC does not consider the practice of ‘visual inspection only’ to be non-compliant with the requirements of BS-7671,
provided that:
The visual inspection is carried out by an electrically competent person with good knowledge and experience of the electrical

installation practices existing at the time the installation was first constructed.

* The inspection is carried out in accordance with all the requirements of BS 7671 that are applicable to visual inspection.
* The limitations of ‘visual inspection only’ are made clear in writing to the person ordering the work.
* No claim is made that ‘visual inspection only’ can or will fully determine whether an installation is safe for continued use.
* An objective report of the findings of the visual inspection is given to the person ordering the work, whether or not specifically requested by that person.
* The scope of the condition report includes all the aspects of the model periodic inspection report given in BS 7671 which are relevant to visual inspection.
* Visual condition reports do not include items that can only be checked with test instruments ( such as the adequacy of earthing arrangements ).
* Any quotation for proposed remedial work is given separately from the visual condition report.
*A full periodic inspection is recommended to the customer if it is suspected that the installation is in an unsafe condition.

 

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THE 17TH EDITION & LOCATIONS CONTAINING ….. ( 2392-10 )

A BATH OR SHOWER

INTRODUCTION
Section 701 of BS7671:2008 The 17th Edition is the new section covering locations containing a
bath or shower. The bathroom regulations Section 601 of the 16th Edition were based on the draft
international standard IEC 364. The 17th Edition has been based on both IEC 364 Section 701 and
the new European harmonised document HD 384 Part 7, within Section 701 of the 17th Edition.
HD 384, Section 701 has been published. The 17th Edition absorbs the regulations in these standards.
As with the 16th Edition, regulations in 701 are specific requirements that add to or modify the general
requirements of Parts 3, 4 & 5. The numbers following the section number relate to the chapter and
sections of the general parts e.g. 701.415.2 supplementary equipotential bonding is an extension of
section 415.2 in Chapter 41.
The scope of Section 701 is the same as the 16th Edition, any location where there is a fixed bath or
shower. This includes communal showers and baths in sports facilities and accommodation buildings,
hotels and similar as well as domestic bathrooms. It does not include emergency showers in industrial
areas or laboratories and medical treatment locations. However, there are no special requirements recorded for medical treatment locations. Electrical Contractors’ Association
KEY FACTSHEET
MAIN CHANGES
OMISSIONS FROM 16TH EDITION
601-01 Zone 3 is deleted.
601-04 Supplementary equipotential bonding is not required provided that all circuits at the location are
protected by a 30 mA RCD and there is continuity between the extraneous-conductive-parts and the
protective equipotential bonding.
601-07 Wiring systems is deleted.
There are no restrictions as to where cables may be installed but any surface enclosures, including
trunking, installed in the zones must have minimum rating IPX4.

ADDITIONS
701.411.3.3 Additional protection by 30 mA RCDs is required for all circuits serving equipment in the location.
701.512.3 Low voltage socket-outlets may be installed, but must be at least 3 m from the zone 1
boundary and protected by a 30 mA RCD.
701.753 Particular requirements for electric floor heating systems.

DETAILS OF REQUIREMENTS
ZONES
701.32.1 The upper height limit of all zones is 2.25 m. Above 2.25 m is outside of all zones.
701.411.3.3 ADDITIONAL PROTECTION BY RCDS
All circuits must be protected by RCDs. A single RCD may protect a group of circuits.

THE 17TH EDITION & LOCATIONS CONTAINING
A BATH OR SHOWER
INTRODUCTION
Section 701 of BS7671:2008 The 17th Edition is the new section covering locations containing a
bath or shower. The bathroom regulations Section 601 of the 16th Edition were based on the draft
international standard IEC 364. The 17th Edition has been based on both IEC 364 Section 701 and
the new European harmonised document HD 384 Part 7, within Section 701 of the 17th Edition.
HD 384, Section 701 has been published. The 17th Edition absorbs the regulations in these standards.
As with the 16th Edition, regulations in 701 are specific requirements that add to or modify the general
requirements of Parts 3, 4 & 5. The numbers following the section number relate to the chapter and
sections of the general parts e.g. 701.415.2 supplementary equipotential bonding is an extension of
section 415.2 in Chapter 41.
The scope of Section 701 is the same as the 16th Edition, any location where there is a fixed bath or
shower. This includes communal showers and baths in sports facilities and accommodation buildings,
hotels and similar as well as domestic bathrooms. It does not include emergency showers in industrial
areas or laboratories and medical treatment locations. However, there are no special requirements
recorded for medical treatment locations.

THE 17TH EDITION & LOCATIONS CONTAINING A BATH OR SHOWER
701.413 ELECTRICAL SEPARATION
May be used as a protective measure for a single item of equipment or a single socket outlet.
Not to be used with electric floor heating systems.

701.414 EXTRA LOW VOLTAGE - SELV OR PELV
All live parts to be insulated or contained within enclosures, minimum IPXXB or IP2X.

701.415 ADDITIONAL PROTECTION SUPPLEMENTARY EQUIPOTENTIAL BONDING

Where required, supplementary bonding shall connect protective conductors of each circuit to each other
and to accessible extraneous-conductive-parts. This includes: metal water, gas and waste pipes, metallic
air conditioning and heating systems, accessible structural parts of the building.
Metal door and window frames and similar are not normally extraneous-conductive-parts unless connected
to structural steel.
The bonding does not necessarily have to be in the location. It may be an adjacent room (linen cupboard)
or above a ceiling. It must be accessible for inspection, testing and maintenance.

SUPPLEMENTARY BONDING IS NOT REQUIRED AND MAY BE OMITTED:
(i) where main bonding is provided in accordance with 411.3.1.2, and
(ii) all final circuits meet the required disconnection times 0.4 sec for TN systems, 0.2 sec for TT
systems, and
(iii) all circuits have additional protection by 30 mA RCD, and
(iv) all extraneous-conductive-parts (metal water pipes) in the location are electrically continuous
and effectively connected to the protective equipotential bonding.
Where the main pipework of water distribution and central heating systems are pvc, short sections of
copper pipes connecting taps, radiators and the like are not considered to be extraneous-conductive parts
because they are unlikely to introduce Earth to the location. Supplementary bonding is therefore
not required.
Supplementary equipotential bonding is unlikely to be required on a new installation. It may be required
where alterations and additions are being made to an installation (it may already in place). In this
situation, circuits that are not being affected by the alterations do not require upgrading to meet the
requirements of 701.411.3.3 protection by 30 mA RCD.

701.5 SELECTION AND ERECTION OF EQUIPMENT, SWITCHGEAR AND CONTROLGEAR

701.512.2 EXTERNAL INFLUENCES
The following does not apply to the switches and controls of fixed current using equipment and the cords
of pull cord switches.
All equipment must be suitable for the zone in which it installed.
Requirement for equipment:
(i) Zone 0 - IPX7
(ii) Zones 1 & 2 IPX 4 (except in Zone 2, shaver sockets to BS EN 61558-2-5 located where
direct spray from showers is unlikely).
(iii) IPX5 anywhere where equipment may be exposed to water jets.
THE 17TH EDITION & LOCATIONS CONTAINING A BATH OR SHOWER
701.512.3 ERECTION OF SWITCHGEAR, CONTROLGEAR AND ACCESSORIES
(i) Zone 0 - no switchgear or accessories are permitted
(ii) Zone 1 - only switches for SELV circuits and equipment - max 12V a.c. rms or 30V ripple free
d.c. may be used. Safety source to be outside zones 0, 1 & 2.
(iii) Zone 2 as (ii) above except, shaver sockets to BS EN 61558-2-5 may be fitted.
(iv) 13 amp socket-outlets may be installed, must be at least 3 m from the zone 1 boundary.
13 Amp socket outlets may be
installed 3m horizontally from the
boundary of Zone 1 and must be
protected by a 30mA RCD
*Zone 1 if the space is accessible without the use of a tool.
Spaces under the bath accessible only with the use of a tool
are outside the zones.
OR SHOWER
701.55 CURRENT-USING EQUIPMENT
In zone 0 current-using equipment must
(i) comply with the relevant product standard
(ii) be suitable for use in Zone 0
(iii) installed to manufacturer’s instructions
(iv) be fixed and permanently connected
(v) SELV not exceeding 12 V a.c. rms or 30 V ripple-free d.c. Safety source to be outside Zone 0,1 & 2
In zone 1 current-using equipment must
(i) be fixed and permanently connected
(ii) be suitable for use in Zone 1
(iii) installed according to manufacturer’s instructions
Equipment that may be installed
(i) Whirlpool units
(ii) Electric showers
(iii) Shower pumps
(iv) Equipment protected by SELV or PELV nominal voltage not exceeding 25 V a.c. rms or 60 V
ripple-free d.c.
Safety source to be outside Zone 0,1 & 2
(v) Ventilation equipment
(vi) Towel rails

(vii) Water heaters
(viii) Luminaires
In zone 2 current-using equipment must be
(i) permanently connected, the means of connection must be outside of zone 2
(ii) suitable for use in a location containing a bath or shower
(iii) installed according to manufacturer’s instructions

701.753 ELECTRIC FLOOR HEATING SYSTEMS
Heating cables and thin sheet heating elements must:
(i) comply with relevant product standards
(ii) have a metal sheath, or
(iii) have a metal enclosure, or
(iv) be covered with a fine metal mesh.
Unless the protective measure SELV is applied, metal sheaths, enclosures and grids must be
connected to the circuit cpcs
The protective measure ‘electrical separation’ is not permitted

RCD Ratings :

The rating of an RCD has nothing to do with its ability to handle the current to the appliance or the circuit protected, but is the value of residual current at which it will operate. Thus, an RCD in a typical domestic situation may well be able to switch off the load current of 40A but be rated at a residual current of 30mA ( thirty thousandths of an ampere ). RCDs are made with a wide range of ratings, but by far the most common are 30mA and 100mA

 

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BS 1362 specifies breaking-time/current characteristics only for fuses with a current rating of 3 A (marked in red ) or 13 A (marked in brown ). Examples for the required breaking-time ranges are

• For 3 A fuses: 0.02–80 s at 9 A, < 0.1 s at 20 A and < 0.03 s at 30 A.
• For 13 A fuses: 1–400 s at 30 A, 0.1–20 s at 50 A and 0.01–0.2 s at 100 A.

3 A fuses are intended mainly for small load (< 750 W) appliances, such as radios and lights. 13 A fuses are for larger load (<3.2 kW) appliances such as heating and heavy-duty electric motors , .

BS 1362 requires that plug fuses with any other current rating are marked in black. 5 A fuses are also commonly used, for medium load (1250 W max.)

Syntax Error :
Appears when the figures are entered in the wrong order ,
x2 ↔ Multiplies a number by itself , i.e. 6 x 6 = 36 , on the calculator this would be 6 x2 = 36 , when a number is
multiplied by itself it is said to be Squared ,

x3 ↔ multiplied a number by itself and then the total by itself again i.e. when we enter 4 on calculator x3 = 64 .
when a number is multiplied in this way it is said to be Cubed :

√ ↔ Gives the number which achieves your total by bring multiplied by itself i.e. √ 36 = 6 This is said to be the Square root
of a number and is the opposite of Squared :

3√ ↔ Gives the number which when multiplied by itself three times will be the total , 3√ 64 = 4 this is said to be the Cube root ,

Brackets :
these should be used to carry out a calculation , within a calculation .
Example calculation :
………. 32
( 0.8 x 0.65 x 0.94 )
Enter into calculation 32 ÷ ( 0.8 x 0.65 x 0.94 ) = ?

 

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Utilising the Fault Current 17th Edition : ( Table 41.2 ) Revision :

Sticking with our light circuit scenario and assuming that the light circuit is protected by a 5 amp re-wireable type fuse then the maximum allowable earth fault loop impedance given by BS-7671 wiring regulations is 9.58Ω. This value is for the total resistance in the fault loop described above.

Ohms Law : it is fundamental to electrical design and I will show you why. Ohms Law states that when current flows through a load or Résistance then the voltage that you can measure across the load will be equal to the product of the Résistance and current.

Simply, VOLTAGE = RESISTANCE X CURRENT which is normally shortened to V=IR or I=V/R or R=V/I (/ means divided by for non-mathematic persons )

We can now use Ohms Law to calculate the fault current for our maximum earth fault loop impedance of 9.58Ω that we extracted from the wiring regulations knowing that the supply voltage to our house is 230V.

Using I=V/R we have I = 230V ÷ 9.58Ω and a few taps of the calculator gives the current as 24 amps.

Thus, 24 amps of current is going to flow through a 5 amp fuse. The fuse wire gets hot, melts and breaks the circuit. So we have an Automatic Disconnection of Supply or ADS.

Basic Protection :

Protection against electric shock under fault free conditions. (I.E. provision of insulation on wires and plastic covers on equipment)
Used to be referred to as Direct Contact which was the contact of persons or livestock with live parts which may result in electric shock. Basically, if live parts are such as conductors and terminals are protected by insulation (basic protection) then a person cannot come into direct contact with lethal voltages.

Residual Current Device: 2392-10

When you turn an appliance on such as a cooker, it places a load on the electrical circuit and current flows through the load which provides the heat. Current flows down the live or LINE conductor and returns along the NEUTRAL conductor back to the origin of the supply.

The current that returns up the neutral from the load should equal the current that flows down the line to the load.

If there is a difference in theses currents then current is being 'lost' somewhere and this will be a leakage to earth. If this leakage to earth is via you then you may be receiving an electric shock.

The RCD cleverly monitors the current flowing out and the current flowing back and if they differ by an amount determined by the rating of the RCD then it automatically disconnects the supply.

RCDs used to protect sockets and wiring in an domestic installation are rated at 30mA (milli amps).

Apprentice :
Continuity in the protective earth conductor.

There are no breaks so for instance, the earth connection on the last light point in the circuit is continuous right back the main earth terminal back at the consumer unit.

Continuity in ring circuits.

To avoid cable being overloaded it is important that the ring is unbroken.

Insulation Resistance.

Checks to ensure that there are no breakdowns in insulation between live conductor and live conductors and the earth conductor. This test will pick up cable damaged during installation. The circuits are tested at a DC voltage of 500V. ( or 250v d.c SELV / PELV - check table 61 regs ,

Polarity

That there Line, Neutral and Earth conductors are all correctly connected at sockets and light outlets. (check that single pole switches are installed in the Line and not the Neutral)

Earth Loop Fault Impedance

This tests the resistance to a fault current due to a short occurring between Line and Earth. If the resistance is too high a dangerous shock voltage would exist.

Prospective Fault Current

This is the value of current that can flow in your wiring in a fault condition. Values can range from 1000 amps to 16000 amps. circuit breakers and fuses have sufficient rating to interrupt the current.
Operating time for Residual Current Devices (RCDs RCBOs).
We test a 50% of the current rating to check that they do not trip.
We test at 100% and 500% of current rating and record the operating time is within specified limits. If the device does not operate within limits then you could get a shock when you chop your cable with your lawn mower!

Earth Electrode Resistance

This only applies if you do not have an earth connection supplied by the electricity supplier and the earth is provided by a rod driven into the ground. Usually found in more rural locations and known as a TT supply.

How Building Regulations now affect Domestic Electrical Installations : 2392-10

Stay legal with the Building Regulations :

Building Regulations are statutory and you can be prosecuted for failing to comply with them. Failure to comply is in fact a criminal offence.

Building Regulations 2000 Statutory Instrument No. 2531 are made under powers provided in the Building Act 1984 and applies in England & Wales.

The purpose of the Building Regulations is to provide for the Health & Safety of people in and around buildings and also provide for matters such as energy conservation, access and use.

Regulation 4 of the Building Regulations 2000 as amended requires that

4.(1) Building work will be carried out so that:
(a) it complies with the applicable requirements contained in Schedule 1 (Parts A to P); and
(b) in complying with any such requirement there is no failure to comply with any other requirement.
(2) Building work shall be carried out so that after it has been completed:
(a) any building which is extended or to which material alteration is made; or

(b) any building in, or in connection with, which a controlled service or fitting is provided, extended or materially altered; or

(c) any controlled service or fitting complies with applicable requirements of Schedule 1 (Parts A to P) or, where it did not comply with any such requirement, is no more unsatisfactory in relation to that requirement than before the work was carried out.
Amendment No. 2 to the Building Regulations introduced Part P complete with a definition of Electrical Installation

Part P Electrical Safety (Schedule 1 to Building Regulations) - Requirement
Design and installation

P1. Reasonable provision shall be made in the design and installation of electrical installations in order to protect persons operating, maintaining or altering the installations from fire or injury.
Limits of application
The requirements of this part apply only to electrical installations that are intended to operate at Low – Voltage or Extra Low Voltage and are:

(a) in or attached to a dwelling

(b) in the common parts of a building serving one or more dwellings, but excluding power supplied to lifts

(c) in a building that receives its electricity from a source located within or shared with a dwelling; and

(d) in a garden or in or on land associated with a building where the electricity is from a source located within or shared with a dwelling.

So what do these regulations mean where domestic electrical work is concerned ?
Firstly, that electrical work in dwellings is now a controlled service under building regulations because Part P of Schedule 1 sets out the requirement P1 as detailed above which means that failure to satisfy the requirements is an offence.

Secondly, for electrical work you use the guidance offered in Approved Document P , Electrical Safety – Dwellings , for the purpose of complying with P1. Furthermore, the guidance advises that the requirement of P1 will be met by adherence to the 'Fundamental Principles' for achieving safety given in BS-7671 chapter 13 so effectively giving a statutory status to BS -7671.
Thirdly, you must also take into account other parts of schedule 1 which will be invoked by activities carried during electrical installation work.

These are:
Part A - Structure
Depth of chases in walls and sizes of holes and notches in joists

Part B - Fire Safety
Provision of fire alarm and fire detection systems, fire resistance of penetrations through floors and walls

Part C - Site Preparation
Resistance to moisture of cable penetrations through walls

Part E - Resistance to Passage of Sound
Installations must not degrade the resistance of passage to sound in the building

Part F - Ventilation
When adding extractor fans

Part L1 - Conservation of Fuel and Power
Lighting systems to be supplied with appropriate lamps and controls so that energy can be used efficiently

Part M - Access and facilities for the disabled
Heights of switches and socket outlets.

For example - you live in a flat with another flat above you. You decide to have some downlighters fitted into the ceiling of your lounge.

Account must be taken of Part B - Fire Safety regarding fire resistance as the ceiling will be penetrated to fit the downlighters thus weakening the fire barrier and resistance to the spread of fire.

Also Part E - Resistance to Passage of Sound must be observed as the ceiling provides an acoustic barrier.
To deal with this particular installation problem there are available on the market fire rated mains and low voltage downlighters which comply with both Part B and E requirements.

 

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2392-10
*Applicable with effect from the 1st July 2008 when new 17th edition of BS-7671 ,

Defects in the existing installation that effect the safety of the alteration or addition must be made good.

Most likely Defects to be found which will affect New Work

No : Main Protective Bonding Conductor :
No : Supplementary Protective Bonding Conductors ( where Required ) in bathroom but now requires RCD protection*
No : RCD Protection on sockets*
No : RCD Protection for buried cables in walls*

Alternating Current (AC)

The mains supply current waveform is a sine wave which has the form , ↔ One Cycle ↔ It repeats 50 cycles every second which using the international symbol for frequency is written as 50 Hz
Amplitude / Time !!!!

Fault finding & Breakdowns :
Electrical fault finding by it's very nature is a process of elimination.

Firstly the customer reporting the fault will be asked some seemingly simple questions such as what happened ?, when did it happen? What usually happens? What isn't happening now etc.

Then an inspection will take place looking for signs of wear and tear, mechanical damage to cables or accessories, signs of overheating, corrosion, burning and even listening for strange noises from equipment etc.

If the problem is not evident after the initial visual check then some electrical testing will have to take place in order to find the fault in the hidden cables. This can be a time consuming process and will mean isolation of the supply for a time.
Once the fault is identified it can then be rectified. This may mean a new component or accessory or even replacement of the faulty cable.

RCDs : Apprentices’ ,

One of the major changes in the 17th Edition of the IEE Wiring Regulations is the requirement of RCD's to protect circuits where the cables are buried in walls at a depth of less than 50mm and not mechanically protected. In a domestic property this is likely to include most if not all the circuits.

So what exactly is an RCD ?

An RCD is an electrical safety device specially designed to immediately switch the electricity off when electricity "leaking" to earth is detected at a level harmful to a person using electrical equipment. An RCD offers a high level of personal protection from electric shock. Fuses or overcurrent circuit breakers do not offer the same level of personal protection against faults involving current flow to earth. Circuit breakers and fuses provide equipment and installation protection and operate only in response to an electrical overload or short circuit. Short circuit current flow to earth via an installation's earthing system causes the circuit breaker to trip, or fuse to blow, disconnecting the electricity from the faulty circuit. However, if the electrical resistance in the earth fault current path is too high to allow a circuit breaker to trip (or fuse to blow), electricity can continue to flow to earth for an extended time. RCDs (with or without an overcurrent device) detect a very much lower level of electricity flowing to earth and immediately switch the electricity off.

RCDs have another important advantage - they reduce the risk of fire by detecting electrical leakage to earth in electrical wiring and accessories. This is particularly significant in older installations.

How they Work :

RCDs work on the principle "What goes in must come out". They operate by continuously comparing the current flow in both the Active (supply) and Neutral (return) conductors of an electrical circuit.
If the current flow becomes sufficiently unbalanced, some of the current in the Active conductor is not returning through the Neutral conductor and is leaking to earth.

RCDs are designed to operate within 10 to 50 milliseconds and to disconnect the electricity supply when they sense harmful leakage, typically 30 milliamps.

The sensitivity and speed of disconnection are such that any earth leakage will be detected and automatically switched off before it can cause injury or damage. Analyses of electrical accidents show the greatest risk of electric shock results from contact between live parts and earth.

Contact with earth occurs through normal body contact with the ground or earthed metal parts. An RCD will significantly reduce the risk of electric shock, however, an RCD will not protect against all instances of electric shock. If a person comes into contact with both the Active and Neutral conductors while handling faulty plugs or appliances causing electric current to flow through the person's body, this contact will not be detected by the RCD unless there is also a current flow to earth.

On a circuit protected by an RCD, if a fault causes electricity to flow from the Active conductor to earth through a person's body, the RCD will automatically disconnect the electricity supply, avoiding the risk of a potentially fatal shock.

Examples of equipment recommended to be protected by a RCD:

• Hand held electric power tools, such as drills, saws and similar equipment.
• Tools such as jack-hammers, electric lawn mowers.
• Equipment on construction sites.
• Equipment such as appliances which move while in operation, such as vacuum cleaners and floor polishers.
• Appliances in wet areas such as kitchens, including kettles, jugs, frying pans, portable urns, food mixers/blenders.
• Hand held appliances such as hair dryers, curling wands, electric knives etc.
• Cord extension leads.

PAT (Portable Appliance Testing)
Inspecting & Testing will be carried out in accordance with the requirements of the following regulations and publications:

Electricity at Work Regulations 1989 :
Health and Safety at Work etc. Act 1974 :
The Code of Practice for In-service Inspection and Testing of Electrical Equipment
The Provision and Use of Work Equipment Regulations 1998 :

Basic fault finding :

Lighting circuits which won't reset.
A common fault is a short circuit on the bulb holder which can get damaged by heat which also makes the cable brittle and then the insulation fails.

unscrew the plastic ceiling rose to check for any signs of corrosion on the wires possibly as a result of some dampness

.2392-10

Possible rewireable fusebox upgrades may also bring to the home owners attention, common hazards such as that of a lighting circuit which DOES NOT have a earth. Where metallic switches ( brass silver etc..) or metallic light fittings are present, there is a risk of electric shock under earth fault conditions.

***URGENT ATTENTION*** is therefore a recommendation.

Also the requirement of 10mm main equipotential earth bonds to gas mains / water mains

2392-10 : Wording for Clients Amber ,

Before
consumer units/fuseboards do not meet current British Standards. This can be due to visible damage e.g., broken fuse carriers, no residual circuit device (RCD) protection, no capacity for additional circuits (requires more circuit ways), or the consumer unit has a wooden back which can be a fire hazard or cable joints which are not terminated properly and are live and exposed. This can be a major factor in causing an electrical fire.

After
consumer units which DO meet British Standards. These consumer units are protected by an RCD (Residual Current Device) which will give you better protection to accommodate the upgrade along with the necessary MCBs (mini circuit breakers) to suit. This gives overload and short circuit protection for the final circuits, as well as the capability of disconnecting a faulty circuit at a faster tripping time

PSCC is Measured as 0.09 Ohm then at a voltage of 230V a fault current of 2555.5A will flow. ( 230 ÷ 0.09 = 2555.6A )

 

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All Main Protective Bonding Conductors are Tested for Continuity.

This is of course done with the System off-Line. You NEVER, EVER, Disconnect Main Protective Bonding Conductors on a Live Installation !

The Résistance of these Conductors should as Low as Possible.

Different classifications of MCB will give different results.

Type 1 requires between 2.7 and 4 times overload current to trip inrequired time. Type 2 requires 4-7 times and type B 3 - 5 times. In all cases you should assume that your MCB is on the upper limit.

* Overload Current can be caused when a) → Excessive mechanical load is applied to an electrical motor← b) a forward/reverse controller attempts to switch a motor to both directions simultaneously c) contamination of a motor terminal bock results in tracking d) an electrician drill through a busbar chamber and touches a live busbar with the drill.

* Current Co-ordination between Conductors and Overcurrent Protection Device is Achieved when a) → In is not less than Ib ← b) In is greater than Iz c) the current causing effect operation (Iz) exceeds 1.45 I2 d) Ib > Iz

* Fireman's Emergency Switches are Provided for the Switching off of a) factory low voltage burglar alarm systems b) interior low voltage discharge lighting systems c) → exterior lighting systems exceeding low voltage ← d) factory fire alarm circuits operating at low voltage.

1 a , 2 a , 3 c Regulation 537.6.3

11 Final ring-circuit wiring can be described as the wiring between a) The cutout-fuse and the electric meter b) the main switch and distribution board c) the distribution board and current using equipment d) the supply cut-out fuse and the remotest point of utilization. 12 A ring final sub-circuit is run in pvc conduit. How many single core cables are required? a) 3 b) 4 c) 5 d) 6 14 An earth conductor is connected to the supply sheath of a lead armoured cable at a hospital intake. Is this system a) TT b) TN-C c) TN-S d) TN-C-S 15 An electric fire having an element exposed to touch would allow the risk of an electric shock by a) prospective contact b) earthing contact c) indirect contact d) direct contact. 18 An extra-low-voltage system is electrically separated from earth is called a) F.E.L.V. b) **** S.E.L.V. c) non-conducting d) earth free.

11 c : 12 , 6 (2 x brown ) (2 x cpc ) (2 x blue ) : 14 c TN-S see page 33 : BS 7671:2008 : 15 d direct contact 18 definitions , p-29

4 A d.c. voltage of 120V between conductors is classified as being a) extra-low voltage b) Low-voltage c) Reduced-low-voltage d) S.E.L.V.
6 Which of the following describes a TN-C-S system a) earthing is independent of the supply cable b) the consumers earth terminal is connected to the incoming cable sheath c) protective and neutral conductors are combined d) supply system has no earth
8 Which of the following is NOT a classification of external influences? a) Current rating b) Environmental conditions c) Construction of a building d) Utilization.
10 An electrical installation should be arranged in such a way as to avoid hazards in the event of a fault and to allow safe operation, maintenance and testing when required. One method of complying with this is to a) Connect all circuits as radial circuits b) Connect all circuits as ring final sub-circuits c) Divide the installation into separate circuits d) divide the installation into categories of circuits

4 b see Part 2 definitions 'low voltage' : 6 c TN-C-S : p – 33 : 8 a refer to appendix 5 BS 7671:2008 p – 318 : 10 c see Regulation 314.1.

The principle of SELV is that by reducing the voltage to 50V or below the risk of electric shock is reduced and additionally with SELV the equipment supplied through a BS-EN 61558-1 transformer will have no return path to the source given that there is no connection to earth. Regulations within BS 7671 regarding the use of SELV as a protective measure can be found in Chapter 41 specifically regulation 414.1 / 414.4.5

Insulation Resistance :

* Before testing check:
* Pilot or indicator lamps should be disconnected
* Voltage sensitive equipment should be removed, such as dimmer switches, timers, controllers, starters and RCDs*
* Lamps should be removed
* There is no electrical connection between any phase, neutral or protective conductor
Insulation Resistance Method
* Set the instrument to the Megohms scale

* MΩ (Millions of ohms)
* Test voltage 500v

* Readings should be 1.0MΩ but should be investigated below 2 MΩ

Insulation Resistance
* Test between the phase and neutral conductors connected together and earth at the consumer unit

* For circuits containing 2 way or 2 way and intermediate, switched must be operated one at a time and the circuits subjected to an additional test

Insulation Resistance
* Conducted to detect short circuits and high resistances in circuits

* Considered a ‘pressure test’, putting approximately twice the nominal voltage through a completed circuit

Zero or Null leads

* When measuring the resistance of a length of cable, we must take into account the resistance of the leads
* Null the leads
* If it is an older instrument, we need to take the reading of the leads and subtract it from the total reading of the measured length of cable

 

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Dimmer Buzzing :

If you hook up a really cheap dimmer switch, you may notice a strange buzzing noise. This comes from vibrations in the bulb filament caused by the chopped-up current coming from the triac.
you know that electricity flowing through a coiled length of wire generates a substantial magnetic field, and fluctuating current generates a fluctuating magnetic field. If you've read How light Bulbs work , you know that the filament at the heart of a light bulb is just a coiled length of wire. It makes sense, then, that this coiled filament becomes magnetic whenever you pass current through it, and the magnetic field fluctuates with the AC current.

Normal undulating AC current fluctuates gradually, so the magnetic field does, too. The chopped-up current from a dimmer switch, on the other hand, jumps in voltage suddenly whenever the triac becomes conductive. This sudden shift in voltage changes the magnetic field abruptly, which can cause the filament to vibrate -- it's rapidly drawn to and repelled by the metal arms holding it in place. In addition to producing a soft buzzing sound, the abruptly shifting magnetic field will generate weak radio signals that can cause interference on nearby TVs or radios !

Better dimmer switches have extra components to squelch the buzzing effect. Typically, the dimmer circuit includes an inductor choke, a length of wire wrapped around an iron core, and an additional interference capacitor. Both devices can temporarily store electrical charge and release it later. This "extra current" works to smooth out the sharp voltage jumps caused by the triac-switching to reduce buzzing and radio interference.

Some high-end dimmer switches, such as the ones commonly used in stage lighting, are built around an autotransformer instead of a triac. The autotransformer dims the lights by stepping down the voltage flowing to the light circuit. A movable tap on the autotransformer adjusts the step-down action to dim the lights to different levels. Since it doesn't chop up the AC current, this method doesn't cause the same buzzing as a triac switch.

There are a lot of other dimmer switch varieties out there, including touchpad dimmers and photoelectric dimmers, which monitor the total light level in a room and adjust the dimmer accordingly. Most of these are built around the same simple idea -- chopping up AC current to reduce the total energy powering a light bulb. At the most basic level, that's all there is to it.

Some high-end dimmer switches, such as the ones commonly used in stage lighting, are built around an autotransformer instead of a triac. The autotransformer dims the lights by stepping down the voltage flowing to the light circuit. A movable tap on the autotransformer adjusts the step-down action to dim the lights to different levels. Since it doesn't chop up the AC current, this method doesn't cause the same buzzing as a triac switch.

There are a lot of other dimmer switch varieties out there, including touchpad dimmers and photoelectric dimmers, which monitor the total light level in a room and adjust the dimmer accordingly. Most of these are built around the same simple idea -- chopping up AC current to reduce the total energy powering a light bulb. At the most basic level, that's all there is to it.


* An inductor is about as simple as an electronic component can get -- it is simply a coil of wire. It turns out, however, that a coil of wire can do some very interesting things because of the magnetic properties of a coil :
In a way, a capacitor is a little like a battery. Although they work in completely different ways, capacitors and batteries both store electrical energy. If you have read , then you know that a battery has two terminals. Inside the battery, chemical reactions produce electrons on one terminal and absorb electrons on the other terminal. A capacitor is much simpler than a battery, as it can't produce new electrons -- it only stores them.

Incandescent lamp physics

A typical incandescent lamp take power and uses it to heat up a filament until it will start to radiate light. In the process about 10% of the energy is converted to visible light. When the lamp is first turned on, the resistance of the cold filament can be 29 times lower than it's warm resistance. This characteristic is good in terms of quick warmup times, but it means that even 20 times the steady-state current will be drawn for the first few milliseconds of operation. Lamp manufacturers quote a typical figure for cold lamp resistance of 1/17 th of the operational resistance, although inrush currents are generally only ten times the operational current when such things as cable and supply impedance are taken into account. The semiconductors, wiring, and fusing of the dimmer must be designed with this inrush current in mind. The inrush current characteristic of incandescent (tungsten filament) lamps is somewhat similar to the surge characteristic of the typical thyristors made for power controlling, making them a quite good match. The typical ten times steady state ratings which apply to both from a cold start allow many triacs to switch lamps with current ratings close to their own steady state ratings.

Because lamp filament has a finite mass, it take some time (depending on lamp size) to reach the operating temperature and give full light output. This delay is perceived as a "lag", and limtis how quicly effect lighting can be dimmed up. In theatrical application those problems are reduced using preheat (small current flows through lamp to keep it warm when it is dimmed out).

The ideal lamp would produce 50% light output at 50% power input. Unfortunately, incandescents aren't even close that. Most require at least 15% power to come on at all, and afterwards increase in intensity at an exponential rate.

To make thing even more complicated, the human eye perceives light intensity as a sort of inverse-log curve. The relation of the the phase control value (triac turn on delay after zero cross) and the power applied to the light bulb is very non-linear. To get around those problems, most theatrical light dimmer manufacturers incorporate proprietary intensity curves in their control circuits to attempt to make selected intensity more closely approximate perceived intensity.

“ Resistance Ohmmeters “

Once a month, take a measurement of each Resistor. Over a period of time, show how the instrument is performing , ( Set of low-value resisters )

i.) Low-resistance ohmmeters A set of suitable resistors could be used to assess the instrument; suitable values could be 0.5 Ohms , 0.1 Ohms and 10 Ohms

i.) High-Résistance ( Insulation Résistance ) Ohmmeters A set of suitable Resistors could be used to assess the Instrument; suitable values could be 0.5MΩ 1.0MΩ and 10MΩ.

The Resistor values chosen merely reflect common bands of Résistance that are generally encountered when Testing Electrical Installations. Other values of Résistance, indeed, greater numbers of Resistors, could be used to assess Résistance Ohmmeters across the spectrum of Résistance.

“ Each Resistor on a Connector block ( Test your Instrument ) “

 

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Wiring Regulations in brief :

The Building Regulations , Part P ( which is based on the Fundamental Principles set out in Chapter 13 , BS-7671:2008 ,
In addition , all fixed electrical installations ( i.e. wiring and appliance fixed to the Building fabric such as Socket-Outlets ,
Switches , Consumer Units , and Ceiling fittings ) must now be designed , installed , Inspection , Tested and Certified to BS-7671

Part P of the Building Regulations also introduces the requirement for the cable core colours of all a.c. power circuits to align with BS-7671

Note : Part P only applies to fixed electrical installations that are intended to Operate at Low-Voltage or Extra-Low-Voltage which are not controlled by the Electricity Supply Regulations 1988 as Amended , or the Electricity at Work Regulations 1989 as Amended ,

Why dead tests ?

* Dead tests are performed on an installation prior to energisation
* A dead test will, if carried out correctly, identify faults with a circuit or installation that may be dangerous when energised ,




High value of prospective short circuit current can vary dramatically due to small changes in impedance.

Example: V = Z x I
Therefore: I = 230/0.03 = 7666 Amps
OR: I = 230/0.01 = 23 000 Amps
Notice the vast change in current for a very minor difference in impedance. Obtaining accuracy at very
low impedances is very difficult and a high current is required.

Electrical measuring instruments : ?

( V ) ↔ ( Iv )
R → Ir
( A ) → I

Voltmeter current Iv = V ÷ Rv = 60 ÷ 500 = 0.12A
Resistor current Ir = I – Iv = 5 sub 0.12 amperes = 4.88A
True Value = V ÷ Ir = 60 ÷ 4.88 ohms = 12.3Ω

An alternative method for the second part of this exercise is to consider that the apparent resistor value , 12Ω
Consists of the voltmeter Résistance , 500Ω , in parallel with the unknown resistor R ,

1 ÷ 12 = 1 ÷ 500 + 1/ R
1 / R = 1 ÷ 12 = 1 ÷ 500 = 500 – 12 ( 500 x 12 ,

Therefore : R = 500 x 12 ohms = 6000 ohms
…………………500 – 12 ………. 488 ……...... 12.3Ω

In practice, the most common instances of faulty earthing are:

* Earth connections broken accidentally or corroded through age.
* Earth connections incorrectly made.
* Earth connections not made at all.
* Earth connections removed for some specific purpose and not reinstated.

Double Insulated Equipment: Definitions , p-21

Class II electrical equipment has all exposed metalwork separated from the conductors by two layers of insulation, so that the metalwork cannot become live. There is no earth connection and the operator's safety depends upon the integrity of the two layers of insulation.

PAT , Testing ,
Visual Checks on Hand-Held Portable Equipment Before Use :

Cable :
Signs of mechanical damage, overheating or corrosion
Hardening of outer insulation
Kinking of cable
Coiling of long lengths of cable
A situation where future mechanical damage or corrosion is likely

Plug :
Wires connected to correct terminals and of the correct length
Un-insulated ends of wires completely covered by the screws
Securing screws suitably tight
Fuse of correct rating fitted

Equipment :
Metal casing damaged
Grommet, or other protection at place where cable passes through the casing, damaged or missing
Plastic casing of double insulated equipment damaged
Damaged or defective switches

Note:
An RCD only protects against a Phase to Earth, or a Neutral to Earth fault. It does not protect against a Phase to Neutral fault.

Load Factor

The ratio of the energy actually consumed by a lighting installation over a specified period of time to the energy that would have been consumed had the lighting installation always been operating during the period of time.

Certification

BS 7671 (The Wiring Reguations) states that on completion, all electrical work must be inspected and tested to verify the installation prior to it being energized. A record of this process must be produced in the form of a certificate.

2392-10 rewires ,


Chasing

Electric cables are generally run under floorboards, in the loft and in walls to the electrical accessories. This means that any cables that need to run up or down a solid wall need to be ‘chased in’. Chasing in involves cutting a channel around 25mm wide and 25mm deep into the wall using a special power tool.
Cavity Walls

Some internal walls are not solid but are plasterboard cavity walls. These walls cannot be chased in the conventional way so an alternative method is used. This involves creating holes in the wall at intervals to enable the running of the cables down or up to an accessory.
Floorboards

In order to install cables under floors, carpets will need to be rolled back and the floorboards will have to be lifted. Sometimes the full length of a floorboard cannot be lifted and so it will be cut so that a smaller piece can be removed. Obviously, this would not be done without consulting the homeowner first. Once the cables are in position the board would then be replaced and refixed.
Moving Furniture

Obviously in an inhabited house. There is lots of furniture which could get in the way of access to walls, floorboards etc. It is the homeowners responsibility to move any furniture, beds and the like away from the areas where they are intending to have an electrical accessory. If this is not possible then it can be moved by the electrician. This is an extra to the rewire quote and is charged at an hourly rate. No liability is accepted for any damages to the furniture incurred during this process.

Dust and debris

The processes of chasing walls, making holes and lifting floorboards creates dust and mess and the homeowner must be aware of this. This is kept to a minimum when chasing using a dust extraction system and the liberal use of dust sheets to protect floor coverings. Any dust and debris will be hovered up and removed by the electrician after each days work.

Making Good

Once the whole house has been rewired any chases will need to be filled with plaster and any wholes filled. The homeowner will need the services of a plasterer to do this or alternatively the electrician can do it. This is charged at an hourly rate and would not be to a professional plasterers standard.
Second Fix

The final job to be done, once the plaster has dried, is connect all the electrical accessories and install the customers consumer unit (Fuse board). Then transfer the supply from the old installation to the new. At this point any old accessories and wiring would be removed and the chases left by them filled once again with plaster.

RCDs
have another important advantage - they reduce the risk of fire by detecting electrical leakage to earth in electrical wiring and accessories. This is particularly significant in older installations.

( diversity on domestic cookers is to take the load as 10A plus 30% of the remainder of the actual maximum load, then add a further 5A if there is a socket on the cooker unit )

Q: Do I need to carry out an external fault loop impedance (ze) test? Can I just use the declared values from the distributor ? :

A: A direct reading of Ze is always required. This test establishes that the intended means of earthing is actually present. The distributors’ declared values only give an indication of the maximum Ze that would normally be expected on their networks. It doesn’t guarantee that there is not a problem. For instance the earthing

 

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Fundamental Requirements for safety :

The following is a list of basic requirements

1) use good workmanship ,
2) Use approved materials and equipment ,
3) Ensure that the correct type , size and current- carrying capacity of cables are chosen ,
4) Ensure that equipment is suitable for maximum power demanded of it ,
5) Make sure that conductors are insulated , and sheathed or protected if necessary , or are placed in a position to prevent danger ,
6) Joints and connections should be properly constructed to be mechanically and electrically sound ,
7) Always provide overcurrrent protection for every circuit in an installation ( the protection for the whole installation is usually
Provided by the distribution Network Operator , ( DNO ) and ensure that protective devices are suitably chosen for there location and duty they have to perform ,
8) Where there is a chance of metalwork becoming live owing to a fault , it should be earthed , and the circuit concerned should
Be protected by an overcurrent device or a residual current device ( RCD )
9) Ensure that all necessary bonding of services is carried out ,
10) Do not place a fuse , a switch or a circuit breaker , unless it is linked switch or circuit breaker , in an earthed neutral conductor ,
The linked type must be arranged to break all the line conductors ,
11) All single-pole switches must be wired in the line conductor only ,
12) A readily accessible and effective means of isolation must be provided so that all voltage may be cut off from an installation or any of its circuits ,
13) All motors must have a readily accessible means of disconnection ,
14) Ensure that any item of equipment which may normally need operating or attending by persons is accessible and easily operated ,
15) Any equipment required to be installed in a situation exposed to weather or corrosion , or in explosive or volatile environments , should be of the correct type for such adverse conditions ,
16) Before adding to or altering an installation , ensure that such work will not impair any part of the existing installation and that
The existing is in safe condition to accommodate the addition ,
17) After completion of an installation or an alteration to an installation , the work must be inspected and tested to ensure ,
As far as reasonably practicable , that the fundamental requirements for safety have be met ,

Re-vision : Apprentices

* A visual test will also be needed if the test has been carried out to the front of the sockets, and not behind
them, i.e., removing the faceplate screws and testing from behind.

There are 2 methods that can be adopted when conducting a polarity test. These are described below.

Method 1 :
This method is exactly the same as test method one for ‘Continuity Of Protective Conductors’ if we take
a lighting circuit , figure 1, by putting a temporary link between phase and cpc, at the consumers unit and our instrument at lamp holders themselves, we are creating a circuit. When we operate the light switch, the instrument
changes, and then changes back to the original reading on operation of the switch again. If the reading did
not change, then the switch is likely to be connected in the Neutral. ↔ ( Not good! ) ↔ With a little foresight this could be carried out at the same time as the continuity test. The only difference being, for radial circuits every point must be tested.
The main benefit with this is it allows you to conduct (2 ) tests at the same time, polarity and R1 + R2.

( 2392-10 -&- ↔ for radial circuits every point must be tested. )

Method 2
This method, like wise is similar to test 2 of the continuity test, we simply use a wander lead as the return lead.
There is little use for this method, within the polarity test. Method 1 is less clumsy, and is far more flexible and useful.
(see figure 2).

A Note on radial socket outlets
We have covered ring final circuits, but radial final circuits involving sockets can prove to be little more involved.
Why ? You may ask, well simply because doing a polarity check using method 1, will not uncover a phase to cpc reversal. If the phase and cpc were reversed at the socket, the instrument will still
provide a reading (Figure 3). It will however tell you if you have a phase to neutral reversal ( you wouldn’t have a reading at the socket ). So what can we do to expose a phase – cpc reversal? We can simply link the phase and neutral together at the board, and put our instrument across phase and neutral at the socket, if the cpc and
phase have been reversed, then no reading will be recorded on the instrument. This one takes a while to get your head around ,

Test Method 1 : figure 1

1. Create a temporary link between the phase and the CPC within the consumer unit
2. At each point on the circuit, connect the low resistance ohmmeter to the phase and CPC
3. Operate the switches

Test Method 2 : figure 2).
1. Connect the wander lead to the phase conductor at the furthest point at each point on the circuit ,
2. Connect the low resistance ohmmeter to the phase conductor within the consumer unit
3. Operate the switches

Figure 3 :
Reversed Phase and CPC at socket outlet

 

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Re: Section - 301- Questions - Testing ,

Passing an ECS Health and Safety Assessment is ↔ Compulsory ↔
→→→ For all you Chaps Renewing you ( J.I.B. Card ) ←←← 13 . 11 . 09

SOLAR PHOTOVOLTAIC :


SOLAR ELECTRICITY
The panels produce direct current (DC) which is converted to alternating current (AC) by an inverter so it can be used by appliances in the home. These systems can either be connected to the national electricity grid, or connected to a battery.

THE GENERAL INFORMATION ON SOLAR PHOTOVOLTAIC

“Photovoltaic” is a marriage of two words: “photo”, from Greek roots, meaning light, and “voltaic”, from “volt”, which is the unit used to measure electric potential at a given point.

Photovoltaic systems use cells to convert solar radiation into electricity. The cell consists of one or two layers of a semi-conducting material. When light shines on the cell it creates an electric field across the layers, causing electricity to flow. The greater the intensity of the light, the greater the flow of electricity is.

The most common semi conductor material used in photovoltaic cells is silicon, an element most commonly found in sand. There is no limitation to its availability as a raw material as silicon is the second most abundant material in the Earth’s mass.

A photovoltaic system therefore does not need bright sunlight in order to operate. It can also generate electricity on cloudy days. Due to the reflection of sunlight, slightly cloudy days can even result in higher energy yields than days with a completely cloudless sky.

The power output of a solar array is measured in watts or kilowatts. In order to calculate the typical energy needs of the application, a measurement in watt-hours, kilowatt-hours or kilowatt-hours per day is often used. A common rule of thumb is that average power is equal to 20% of peak power, so that each peak kilowatt of solar array output power corresponds to energy production of 4.8 kWh per day ( 24 hours x 1 kW x 20% = 4.8 kWh )

Fault Currents :

Fault currents arise as a result of a fault in the cables or equipment , there is a sudden increase in current , perhaps 10 or 20 times the cable rating ,
The current being limited by the impedance of the supply , the impedance of the cables , the impedance of the fault and the impedance of the return path , the current is normally of short duration ,

Overload Currents :

Overload Currents do not arise as a result of a fault in the cable or equipment , they arise because the current has been increased by the addition of further load ,
Overload protection is only required if overloading is possible , it would not be required for a circuit supplying a fixed load , but fault protection is required except in exceptional circumstances ( 434.5.1 )

Basic fault finding of fluorescent fittings :

The following checks are recommended to be carried out when checking any suspected faulty fitting.
All checks, apart from 2., should be carried out with the mains supply to the fitting disconnected.

1. Check the ballast / lamp combination
• Ensure the ballast is suitable for the lamp/s being used.
• If the combination is found to be incorrect then it should be determined whether it is actually the ballast or the lamp that is the incorrect item.

2. Check that there is mains supply to the fitting.
• Ensure that the supply not only comes to the fitting, but also goes to the ballast.
• Remember to measure the voltage between Live and Earth, Live and Neutral, and Neutral and Earth.

3. Check that the lamps are in good condition.
• Even new lamps can be faulty.
• Measure each lamp cathode and check for the correct resistance reading.
• The resistance reading should be between 1 - 10Ω, depending on the lamps used.

4. Check that the lamps are inserted into the lamp holders correctly.
• Poor connections will give intermittent operation.

5. Check the wiring of the fitting.
• Are the supply wires connected correctly?
• Are the control wires connected correctly (if used)?
• Check that there are no loose connections.
• Are the lamp wires connected correctly?
• Check this against the wiring diagram on the ballast.
• Check the connections at the lamp holders as well as at the ballast.
• Are the ’ Line ’ and ’ Neutral ’ wires connected correctly?

If the above checks have been carried out and a fault is still evident, replace the ballast.

 

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“ Possible Causes Of RCD Tripping :

Faulty appliance – unplug all electrical appliances, does the RCD reset OK ? If the RCD resets OK plug the appliances back in one at a time. Reset the RCD as you plug each appliance back in to find the faulty appliance.

Electricity can kill – if turning an RCD off to work on a circuit always double check that there is no power in the circuit: ( Lock off )

Incorrect RCD current rating – RCDs have ‘current ratings’ similar to fuses. The current rating is the current that trips an RCD. The current rating of the RCD could be too low.

Poor quality RCD – poor quality RCDs can trip when they shouldn’t.

Items with motors or pumps starting – many items with motors or pumps, for instance showers and pond pumps, cause momentary electrical spikes that are big enough to trip RCDs.

Older washing machines – aging washing machine heating elements can cause momentary electrical spikes that are big enough to trip RCDs.

Certain wash cycle phases – some cycles of the washing machine, for instance the spin cycle, can cause momentary electrical spikes that are big enough to trip RCDs.

Certain dishwasher cycles – some parts of the dishwasher cycle draw a lot of current, a faulty component, for instance the motor, can trip an RCD.

Overloading a washing machine – too many items in a washing machine can cause certain wash cycles, for instance the spin cycle, to trip an RCD.

Fridges and freezers cooling – the fridge or freezer cooling motor starting.

Turning a sun bed on – a sun bed uses a lot of electrical power, the surge in electrical power can trip an RCD.

Turning an heating element on after a long time of being off – moisture in heating elements can trip an RCD, for instance in a sun bed or electric fire. Try resetting the RCD a few times so that the heating element can cause the moisture to evaporate.

Pond pump faulty – pond pumps sometimes have to ‘work very hard’– for instance when they have ‘digested’ part of a plant from the pond. Check your pond pump for blockages.

Moisture in outside electrical distribution boxes – remove the supply and dry the distribution box. Check the weather seals have not perished.

Moisture in outside electrical sockets – remove the supply and dry the electrical socket. Check the weather seals have not perished.

Ice maker on a fridge – a faulty ice maker on a fridge can cause ‘nuisance’ RCD tripping.

De-frost timer on a fridge or freezer – a faulty defrost element on a fridge or freezer can cause ‘nuisance’ RCD tripping.

Central heating elements – faulty heating elements can cause an RCD to trip when they are turned on by a timer.

Moisture in wiring – moisture in the electrical wiring is a common cause of RCD trips. Have you just emptied a bath? Taken a shower ? Is it raining – rain can get into the electrical wiring under the floors or in the loft.

After unplugging all appliances, or turning them off, see if the RCD will reset. If the RCD will reset, the fault is with one of the appliances; if the RCD trips again the fault is with the electrical circuit.

Plug each appliance in one at a time. After plugging the appliance in, or turning an appliance on, reset the RCD; keep plugging the appliances in, and resetting the RCD, until the RCD trips.

Connecting the appliances one at a time, and resetting the RCD in-between, shows the homeowner which appliance is causing the RCD to trip. The homeowner should repair, or replace, the faulty appliance.

Plugging each appliance in one at a time is not a100% guarantee of finding the faulty appliance; it is the best way, but not a 100% guarantee. Certain ‘cause\effect’ situations can suggest a, say, faulty kettle when the real problem is, say, a faulty cooker.

1) Are any electrical circuits working?
2) Has something simple just triggered the switch?
3) A light bulb blowing or light switch arcing can sometimes trip the fuse?

9 times out of 10, an RCD tripping will be in response to something that you (or your family) has just done.
1 out of 10 times, it will be as a result of either physical failure of the device or a build up of fault current which eventually tips the balance.

“ Recessed Light (‘Down Light’) Problems “

* Recessed lights (down lights) have many different wattage ratings. Is the bulb wattage rating correct? Compare the problem bulb, or bulbs, with bulbs that work OK – are they the same?

* Is something covering the bulb housing, for instance loft insulation? Overheating causes many different problems.

* Lights generate a lot of heat – if the lights are ‘recessed’ ensure there is enough space for the heat to dissipate.

* Connect the electrical power input wire to the switch output to bypass the switch – if the light works the switch is at fault.

What Can Go Wrong With A Light Switch

* Loose wiring in switch.

* Switch mechanism broken.

* Damaged wiring.

* Bare wires touching the switch housing.

Symptoms Of A Broken Light Switch With Possible Causes

* Light switch does not work:
* Loose wiring in switch.
* Broken switch.
* Poor connection to light switch terminals.
* Bare wires touching the switch housing.

* Light switch ‘buzzing’ or discoloured:
* Loose wiring in switch.
* Internal arcing.
* Bare wires touching the switch housing.

* Switch hot:
* Loose wiring in switch.
* Bare wires touching the switch housing.

* Lights flickering:
* Loose wiring in switch.
* Poor connection to light switch terminals.
* Bare wires touching the switch housing.

 

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Measures of protection against fire risk with RCDs

RCDs are very effective devices to provide protection against fire risk due to insulation fault. This type of fault current is actually too low to be detected by the other protection (overcurrent, reverse time). For TT, IT TN-S systems in which leakage current can appear, the use of 300mA sensitivity RCDs provides a good protection against fire risk due to this type of fault. An investigation has shown that the cost of the fires in industrial and tertiary buildings can be very great. The analysis of the phenomena shows that fire risk due to electricity is linked to overheating due to a bad coordination between the maximum rated current of the cable (or isolated conductor) and the overcurrent protection setting. Overheating can also be due to the modification of the initial method of installation (addition of cables on the same support). This overheating can be the origin of electrical arc in humid environment. These electrical arcs evolve when the fault current-loop impedance is greater than 0.6 Ωand exist only when an insulation fault occurs. Some tests have shown that a 300mA fault current can induce a real risk of fire

RCDs are very effective devices to provide protection against fire risk due to insulation fault because they can detect leakage current (ex : 300 mA) which are too low for the other protections, but sufficient to cause a fire

Protection when exposed conductive parts are not connected to earth

(In the case of an existing installation where the location is dry and provision of an earthing connection is not possible, or in the event that a protective earth wire becomes broken).
RCDs of high sensitivity (y 30 mA) will afford both protection against indirect-contact hazards, and the additional protection against the dangers of direct-contact.

Determination of voltage drop

The impedance of circuit conductors is low but not negligible: when carrying load current there is a voltage drop between the origin of the circuit and the load terminals. The correct operation of a load (a motor, lighting circuit, etc.) depends on the voltage at its terminals being maintained at a value close to its rated value. It is necessary therefore to determine the circuit conductors such that at full-load current, the load terminal voltage is maintained within the limits required for correct performance.
methods of determining voltage drops, in order to check that:

* They comply with the particular standards and regulations in force
* They can be tolerated by the load
* They satisfy the essential operational requirements

Maximum voltage drop

Maximum allowable voltage-drop vary from one country to another. Typical values for LV installations are given below
A low-voltage service connection from a LV pubic power distribution network , lighting 3% - Other uses ( Heating & Power 5% )
Consumers MV/LV substation supplied from a public distribution MV systems , 6% / 8%

Maximum voltage-drop between the service-connection point and the point of Utilization ,
These voltage-drop limits refer to normal steady-state operating conditions and do not apply at times of motor starting, simultaneous switching (by chance) of several loads, etc. as mentioned in Chapter A Sub-clause 4.3 (factor of simultaneity, etc.). When voltage drops exceed the values , larger cables (wires) must be used to correct the condition.

The value of 8%, while permitted, can lead to problems for motor loads; for example:

* In general, satisfactory motor performance requires a voltage within ± 5% of its rated nominal value in steady-state operation,

* Starting current of a motor can be 5 to 7 times its full-load value (or even higher). If an 8% voltage drop occurs at full-load current, then a drop of 40% or more will occur during start-up. In such conditions the motor will either:

* Stall (i.e. remain stationary due to insufficient torque to overcome the load torque) with consequent over-heating and eventual trip-out

* Or accelerate very slowly, so that the heavy current loading (with possibly undesirable low-voltage effects on other equipment) will continue beyond the normal start-up period

* Finally an 8% voltage drop represents a continuous power loss, which, for continuous loads will be a significant waste of (metered) energy. For these reasons it is recommended that the maximum value of 8% in steady operating conditions should not be reached on circuits which are sensitive to under-voltage problems ,

Legal basis

In England and Wales, the Building Regulations (Approved Document: Part P) require that domestic electrical installations are designed and installed safely according to the "fundamental principles" given in British Standard BS-7671 Chapter 13. These are very similar to the fundamental principles defined in International Standard IEC – 60364-1 and equivalent national standards in other countries. Accepted ways for fulfilling this legal requirement include

* the rules of the IEE wiring regulations ( BS–7671 ), colloquially referred to as "the regs" (BS 7671: 2008, 17th Edition).;

* the rules of an equivalent standard approved by a member of the EEA (e.g., DIN/VDE 0100);

* guidance given in installation manuals that are consistent with BS 7671, such as the IEE On-Site Guide and IEE Guidance Notes Nos 1 to 7.

Installations in commercial and industrial premises must satisfy various safety legislation, such as the Electricity at Work Regulations 1989. Again, recognized standards and practices, such as BS 7671 "Wiring Regulations", are used to help meet the legislative requirements.

Commissioning Certificate

BS-5266 and the European Standard both require written declarations of compliance to be available on site for inspection. These consist of
1. Installation quality.
IEE regulations must have been conformed with and non-maintained fittings fed from the main circuit of the normal lighting system, as required in BS 5266

2. Photometric performance.
Evidence of compliance with light levels has to be supplied by the system designer.

3. Declaration of a satisfactory test of operation.
A log of all system tests and results must be maintained. System log books, with commissioning forms, testing forms and instructions should be provided by the installer.
On completion of the installation of the emergency lighting system, or part thereof, a completion
certificate should be supplied by the installer to the occupier/owner of the premises. The Building Control Department should insist upon a copy of this certificate which will be retained with the Building Regulations Authority.
Maintenance
Finally, to ensure that the system remains at full operational status, essential servicing should be defined. This normally would be performed as part of the testing routine, but in the case of consumable items such as replacement lamps, spares should be provided for immediate use.

Routine inspections and tests

Where national regulations do not apply, the following shall be met.
Because of the possibility of a failure of the normal lighting supply occurring shortly after a period of testing of the emergency lighting system or during the subsequent recharge period, all full duration tests shall wherever possible be undertaken just before a time of low risk to allow for battery recharge. Alternatively, suitable temporary arrangements shall be made until the batteries have been recharged.
The following minimum inspections and tests shall be carried out at the intervals recommended below. The regulating authority may require specific tests.
Daily
Indicators of central power supply shall be visually inspected for correct operation.
NOTE. This is a visual inspection of indicators to identify that the system is in a ready condition and does not require a test of operation.
Monthly
If automatic testing devices are used, the results of the short duration tests shall be recorded.
For all other systems the tests shall be carried out as follows:
a) Switch each luminaire and each internally illuminated exit sign to emergency mode so it uses the battery. This simulates a failure of the supply of the normal lighting and continue for a period sufficient to ensure that each lamp is illuminated.
At the end of this test period, the supply to the normal lighting should be restored and any indicator lamp or device checked to ensure that it is showing that the normal supply has been restored.
NOTE. The period of simulated failure should be sufficient for the purpose of this clause whilst minimising damage to the system components e.g. lamps. During this period, all luminaire's and signs shall be checked to ensure that they are present, clean and functioning correctly.
b) For central battery systems, the correct operation of system monitors shall be checked.
c) For generating sets, refer to the requirement of ISO 8528-12.
Annually
If automatic testing devices are used, the results of the full rated duration test shall be recorded.
For all other systems the following tests made:
a) each luminaire and internally illuminated sign shall be tested as per monthly test but for its full rated duration in accordance with the manufacturer's information;
b) the supply of the normal lighting shall be restored and any indicator lamp or device checked to
ensure that it is showing that normal supply has been restored. The charging arrangements should
be checked for proper functioning;
c) the date of the test and its results shall be recorded in the system logbook;
d) For generating sets, refer to the requirements of ISO 8528-12.