2391 Theory Test Paper

[r10ley]

Hi all, I got given a past exam paper from the 2391 course tutor however it doesnt come with any answers so I thought id put the question and my answers on here to see if im going down the right track and also to help anyone else taking this course so please correct me if im wrong because I probably am.

Q1. BS 7971 requires an inspection to be made on installed electrical equipment during the initial verification. State the three areas to be verified.

A1. .All electrical equipment and materials are of the correect type and comply with all relavent British Standards
.All part of the fixed installation are correctly selected and erected
.No parts of the fixed installation is visually damaged or otherwise defective

Q2. a) Two items of information regarding the protective device at the origin, to be obtained from the distribution network operator.
b) What the designer may take into account when determining maximum demand

A2. a) The rating of the device and its rated short circuit capacity
b) The full load of the installation with diversity applied

Q3. State one statutory and two non statutory publications which relate directly to the inspection and testing process

A3. Statutory - Electricity at work regulation, Non Statutory - BS7671 and Guidance note 3

Q4. A steel conduit and trunking installation has been erected and is to be inspected prior to the installation of cables. State three inspection items which will be checked using the sense of touch.

A4. No sharp edges, conduit is reamed and bushed
Trunking lids are secure
All conduit trucking and accessories are securely fixed

Q5. The electrical installation in a sandwich bar is to be inspected and tested in order for the owner to obtain a license from the local authority. State
a) the two parties with whom the inspector must discuss the requirements for the inspection and test
b) where the outcome of the discussion is to be recorded

A5. a) The local authority and the sandwich bar owner
b) On the periodic inspection report form under extent of installation inspected and limitations.

Q6. List three operational characteristics of a low resistance ohmmeter as identified in guidance not 3.

A6. .No load voltage between 4V and 24V
.Short circuit current not less than 200mA
.Test current a.c and d.c

Q7. a)State two reasons for the prescribed sequence of test prior to energising a new circuit.
b)State one test on an installation forming part of a TT system which may be carried out as either a live test or a dead test.

A7. a)To ensure that the polarity is correct and that no short circuits exist on the installation prior to energising it.
b) Resistance of the earth electrode (Ze)

Q8. State one method of verifying each of the following (each method must be different)
a)Continuity of a lighting circuit CPC
b)Continuity of a main protective bonding conductor 40m in length
c)Continuity of the earthing conductor

A8. a)R1 +R2 test
b)Wandering lead test
c) Ze test

Q9. A conductor of length 50m has a resistance of 2.3mohms/m. A second identical conductor is to be installed in parallel with this conductor. Determine the total resistance of these two conductors when connected in parallel. Show all calcs.

A9. Resistance of conductor = (2.3 x 50)/1000 = 0.115
1/RT = 1/R1 + 1/R2
1/RT = 1/0.115 +1/0.115
1/RT = 17.4
RT = 1/17.4
RT = 0.057 or 57mohms

Q10. State a)two factors which will reduce the insulation resistance of a new installation measured at the distribution board with all the circuits connected.
b)the voltage to be applied when testing the insulation resistance of a 400V ac circuit

A10. a) Number of circuit connected in parallel
b) Length of circuit (decrease when longer)

Q11. A circuit which includes surge protection devices is to be tested to determine insulation resistance. State
a)two methods recognised in BS7671 for safely testing this circuit
b)the minimum test voltage which can be applied

A11. a) Remove surge protection and link out or if not possible test with reduced test voltage
b)250V dc

Q12. An insulation resistance test is carried out on each of the following circuits. State the test voltage to be used in each case.
a)25V SELV lighting circuit
b)650V three-phase motor circuit
c) 110V reduced low voltage circuit

A12. a)250V DC
B)1000V DC
C)500V DC

Q13. State three special locations identified in BS7671 which are divided into zones

A13. Swimming pool, Area containing a bath or a shower, A sauna

Q14. State the appropriate IP protection to be provided for the
a)top surface of a readily accessible motor starter
b)front of a readily accessible distribution board
c)internal barrier within a consumer unit where the cover can be removed without the use of a tool or key

A14. a)IPXXD
b)IPXXB
c)IPXXB

Q15. A BS 1361 fuse is to be used to provide overcurrent and fault protection for a new circuit. State the effect on the operation of the fuse when the following conditions occur if the fuse was installed in the neutral conductor,
a)overload fault
b)earth fault
c)short circuit fault

A15. a)Fuse will operate however the supply will not be cut off
b) The fuse will not operate
c) The fuse will operate but the supply will not cut off

Q16. State a)The test instrument used to measure the earth electrode resistance for
i/ a generator
ii/ an installation protected by an RCD and forming part of a IT system
b)the number of readings to be taken for the test in a)i/ above.

A16. a) i/Earth electrode resistance tester
ii/Earth loop impedance tester
b) 3

Q17. State a)two methods by which the external earth fault loop impedance (Ze) may be determined
b)one method of determining Zs when direct measurement is not possible (Not Ze)

A17. a)Driect measurement and enquiry
b)Calculation Zs=Ze+(R1+R2)

Q18. State the maximum permitted time/current performance criteria for a 30mA BS EN 61009 RCBO when tested at
a)15mA
b)30mA
c)150mA

A18. a) No trip
b) 300 ms
c) 40 ms

Q19. a) List the two test measurements to be taken in order to determine PFC at the origin of a single phase electrical installation
b) State which of the measured values is to be recorded

A19. a) Prospective earth fault current and Prospective short circuit current
b) The higher of the two

Q20. State three locations in an electrical installation where phase sequence would need to be confirmed

A20. Origin of installation, At the distribution board, At end of final circuit supplying a motor

Well thats the first 20 questions and my fingers are abit sore now lol. My only problem with this course is that some of the questions are so ambiguous half the time I know the answer just cant understand what the question nis answering me. So please if any of my answers are wrong let me know

Thanks

r10ley

 

[Deleted member 26818]

8, I would consider using the terms 'Test method 1' and 'Test method 2'.
9, you have used R1 and R2, which are used to denote the resistance of Line conductors and CPCs. There is nothing in the text of the question to indicate the purpose of the conductors, and as the text states that the second conductor is 'in parallel', it would suggest that the two conductors are doing the same function. Your calculations produce answers that have 15 decimal places, which you have then rounded off. In your first calculation, you have divided by 1000, to produce units that are not used in the text of the question. Finally you have not used brackets within the majority of the calculations.
I believe the question is designed to determine whether you know what the effect of using two identical conductors in parallel would be.
I would just write
2.3 X 50 = 115.
115 / 2 = 57.5mΩ.
57.5 / 1000 = 0.0575Ω. If you want to change units.
10, you have only answered the first part of the question, and you don't need to stae 'in parallel'.
14, I would consider using both IPXXD & IP4X, and IPXXB and IP2X in your answers.
Everything else appears fine.

 

[Electricalserv]

For 8. you could say polarity test aswell as test method 1 & 2

 

[r10ley]

Hi Thanks for your input. When you say test method 1 and test method 2 what does this actualy refer to?

Thanks

r10ley

 

[Electricalserv]

In guidance notes three test metod one is where you join the live and CPC at the DB, then test at every outlet on the circuit between live and earth.

Test Method 2 is the use of a wandering lead. Usually to measure R2 and bonding!

 

[r10ley]

Aaaa ok, gonna type up the other questions because im realy bored at work lol see if im going down the right track

Thanks again

r10ley

 

[r10ley]

The owner of a small industrial unit requires an additional exterior lighting circuit to be installed for security purposes. At the same time the existing electrical installations is to be inspected and tested in order to obtain insurance cover for the premises.
The electrical installation forms part of a 400/230 V TN-C-S system with a Ze of 0.1 ohms and a PFC of 4.6KA. The existing installation comprises 70oc thermoplastic insulated single core copper cables contained within a steel trunking and conduit containment system. A separate CPC is installed for each circuit and is contained within the trunking and conduit.
The three-phase distribution board is located at the origin of the installation and contains a mixture of BS EN 60898 circuit breakers and BS EN 61009 RCBOs.
Below shows information on the resistance if conductors in mohms/m
Conductor csa mohm/m at 20oc
1.5 12.10
2.5 7.41
4.0 4.61
6.0 3.08
10.0 1.83

Q21.
a)List the documents that must be completed and issued to the client on the completion of the electrical work (6 marks)
b)List the parties who would be involved in determining the extent and limitation of the inspection and testing of the existing installation. (3 marks)
c)State where the decision in b) above is to be recorded. (1 mark)
d) i/Title given in law to the inspector
ii/Legal status of the inspector (2 marks)
e)List three items of information which must be available to the inspector regarding the distribution network operators equipment (3 marks)

A21.
a) Electrical installation certificate for new lighting circuit accompanied with schedule of inspections and schedule of test results and a periodic inspection report accompanied by a schedule of inspections and schedule of test results.
b)The insurer, The owner and the Tester
c)On the periodic inspection report
d) i/ Duty Holder
ii/ Competent person
e)Type of earthing arrangement, Supply protective device characteristics (Type and current rating) and External earth loop impedance

Q22.
a)One part of the building has an area where chemical etching and washing down takes place.
i/ List three factors which must be considered when inspecting the containment system in this particular area.
ii/ Identify for each of the factors given in a i/ above the human senses that would best determine compliance (9 marks)
b)The owner has agreed that the whole installation may be isolated in order for testing to be carried out. There has been a period of one hour allocated for this work. List the tests that must be carried out during this period (individual circuits may be isolated after this period). (6 marks)

A22.
a) i/ . System selected and routed to prevent water ingress
. System selected and routed to prevent corrosion caused by chemicals
. No idea of a 3rd?
ii/ .Sight
. Sight
. ?
b) .Global insulation test
. External earth fault loops impedance (Ze)
. Prospective short circuit current
. Prospective earth fault current
. Continuity of main and supplementary bonding

Q23. A test of continuity is to be carried out on the main protective bonding conductor to the gas service located 30m from the origin of the installation. Describe how this test is to be carried out after safe isolation has been completed. Your answer should include:
a)Initial safety precautions
b)Instrument used
c)Test procedure
d)Final safety procedures

A23.
.Inform people testing will be carried out and put up notices
. Remove bonding conductor from main earth terminal to remove parallel paths
. Use low resistance ohm meter ensuring it is in working order
. Null test leads or note resistance
. Use a long wandering lead note resistance or null
. Attach one end of wandering lead to removed bonding conductor
. Walk the lead out to gas pipe
. Attach low resistance ohm meter to other end of wandering lead and onto gas pipe which will also test the integrity of the earth clamp
. Set low resistance ohm meter to low ohms scale and record result
. Reinstate bonding conductor into main earth terminal
. Inform people before the supply is to be reinstated

 

[r10ley]

Q24. A continuity of ring final circuit conductors test is to be carried out on a circuit supplying the office. The circuit is wired in 2.5mm cable with 1.5mm cpc. The loop length of the cable is 65m. All socket outlets are connected directly on the ring. Explain in detail, using the information given in figure 1, the three steps required to confirm the continuity of this circuit.
Your explanation should include the
. test instrument
. test connections and the expected readings at each stage
Show all calculations

A24. The test instrument used is a low resistance ohm meter. First test is an end to end of the line neutral and cpc of the ring. This is confirm all conductors form a complete ring. The expected results are:

Line – line – 2.5mm cable = 7.41 mohm/m
(7.41x65)/1000 = 0.48 ohms

Neutral – Neutral – Same as above

Cpc – Cpc – 1.5mm = 12.1 mohms/m
(12.1x65)/1000 = 0.786 ohms

Next cross connect line and neutral of the ring L1 + N2 and L2 +N1 and test at all socket outlets
Expected readings:

R1+Rn = (r1+rn)/4 = (0.48+0.48)/4 = 0.24 ohms

Next cross connect line and cpc L1 + cpc2 and L2 + cpc1 and test at all socket outlets
Expected readings:

R1+R2 = (r1+r2)/4 = (0.48+0.786)/4 = 0.32 ohms

 

[Deleted member 26818]

21,b) Should be inspector, as your tester wouldn't be expected to have an opinion.
21,c) where on the PIR?
22,a,i) Perhaps the selection and suitabillity of fixings for the containment. Not much point in choosing a containment sytem that is proof against corrosion if the fixings used corrode.
22,a,ii)Touch? The security of fixings could be checked by appropriate tugging.
Could smell be a factor to see whether corrosive gases have entered the containment system?
23,c)Would you not disconnect the conductor at the gas pipe to also negate any parallel paths?

 

[r10ley]

I agree with you bar 23 c). Alot of question you know the answer but forget to actually write down everything you should. With 23 c) ive been taught and read to test with you clip actually on the pipe which will test the integrity of your clamp. The parallel paths will be removed as long as you disconnect from one end I believe.

Thanks for your help

r10ley

 

[SMB]

21/b....the client, the inspector, the local authority.

 

[SMB]

23/c.....Disconnect one end due to parallel paths, test and record, expect a reading of 0.05 ohms.

 

[ridemx27]

hi mate if you havent already got it i would recommend buying the exam success book by the iee made it alot easier for me has two model exams in there with good answers remember there is no specific answers for most of the questions but various answers that will get the marks, or better still if your in essex u can have mine i still have it sittin ere, and im sure there tutor has already told ya this but if not answer all questions with bullet points simple and straight to the point dont write essas u dont have enough time and end up waffling on about stuff they dont wanna know, if this is any help.

 

[SMB]

Thanks for the advice....spose the bible is really GN3 (and spinlondon knows his stuff).

I recon anyone who manages to bodge their way through their 2391 should also know their way through GN8....but thats another story..



im hyper-veti-lating.























is it okay to export an earth from my PME supplly to my out building?

 

[Deleted member 26818]

Depends how close to the edge you are.

 

[brucelee]

Hi mate these are the questions from june 2009 exam I thought they rang a bell lol as i did this exam

 

[r10ley]

Yeah they are couple of the questions are abit of a pig I thought lol. Suppose you can pass all the past papers you want its the one you get on the day that count. O well practicle tomorrow so im going to forget the theory for a couple of days lol.

Cheers for your help

r10ley

 

[SMB]

The more past papers you do the easier the exam will be. Especially the first 20 questions.

Do as many past papers as you can get your hands on.

Understand the earth fault loop diagram for all systems.

Understand continuity of the ring final circuit testing.



Good luck with your practical.

 

[brucelee]

Hi mate good luck you have done ok with most of your answers but use correct terminlology as they will pick you up on it use what is wrote in GN3 and for the continuity of ring final circuits do it in 3 steps
step 1 End to End
step 2 cross connect Line and Neutral
step 3 cross connect line and CPC

do as SMB says and get exam success as many Pat papers you can
cristopher kitchers guide to inspection and testing is a good book and its cheap from amazon think it was £11.55 last time i looked I have loads of books i bought
and this was the one which explained it in easier terms
GN3 is the bible though as this is what its based on
also get acopy of GS38 learn that
memorandum of guidance on Electricity at work regs 1989

and when naming stat and non stat docs use for example

stat
health and safety at work act 1974
Electricity at work regulations 1989
non stat
Guidance Note 3
On- Site Guide
BS7671 or the requirments for electical installations

Safe isolation procedure
tests in sequence
learn how to explain in bullet points to save time with or without diagrams
and as you have above with calcs for the continuity of ring final circuits

from what I have read you shouldnt go far wrong mate

Good luck

 

[Deleted member 26818]

Would you include Part P 2006/10 as statutory in relation to domestic installations?
What about CDM Regulations?

 

[brucelee]

No mate dont think so
this doesnt come up on the 2391 well didnt when i did it last year just the usual ones above

 

[r10ley]

Hi all passed me practical today was easier than I thought it would be yipee. Thanks all for your input ill follow it and keep my fingers crossed!

Thanks

r10ley

 

[Jurasic Spark]

Would you include Part P 2006/10 as statutory in relation to domestic installations?
What about CDM Regulations?

The Building Regs' 2000 is Statutory and all the Approved Docs' included Part P are guidance (and therefore NonStat') on how to comply.

 

[r10ley]

Hi all again. Got my hands on another past paper without answers again so I thought id put it up on here to get some feedback and to help others again.
Q1. List 3 installation details that must be recorded, as identified on a Minor Electrical Installation Works Certificate (3 Marks)
A1.
.Type of earthing arrangement
.Method of fault protection
.Prospective device for modified circuit

Q2. State, for each of the following, if the documents are statutory or non statutory.
a) BS 7671 (1 mark)
b) Guidance Note 3 (1 Mark)
c) Electricity at Work Regulation (1 Mark)

A2.
a) Non Statutory
b) Non Statutory
c) Statutory

Q3. State three items of information, relating to the incoming supply for an electrical installation, that must be recorded on a schedule of test results. (3 Marks)

A3.
.Type of earthing arrangement
.External earth fault loop impedance (Ze)
.Prospective fault current (PFC)

Q4. State three general requirements against which installed equipment must be confirmed when carrying out an initial inspection, as stated in BS7671. (3 Marks)

A4.
.All electrical material and equipment is of the correct type and complies with all relevant British standards
.All parts of the fixed installation are correctly selected and erected
.No parts of the fixed installation are visibly damaged or defective so as to impair safety

Q5. List three non compliances that may be identified during the inspection process using the sense of touch. (3 Marks)

A5.
.Boxes and enclosures not securely fixed
.Terminations of conductors arnt tight
.Conductors overheating because they are underrated

Q6. A test for continuity of protective conductors is required as part of a initial verification on an installation. State
a)What must be confirmed when testing a radial socket-outlet circuit (1 Marks)
b)How the recorded measured value is to be confirmed as satisfactory (1 Mark)
c)One factor that may affect the measured values obtained (1 Mark)

A6.
a)Polarity
b)Added to Ze (Zs=Ze + (R1+R2)) then compared to amended BS7671 values
c)Ambient temperature

Q7. A test is carried out to obtain an R1+R2 value at the furthest point of a two-way lighting circuit. Explain why it is necessary to operate the two way switching during the test. (3 Mark)

A7. To confirm polarity and to ensure there are no breaks in the switch wiring

Q8. A test for continuity of ring final circuit conductors is to be carried out on a circuit containing no spurs. State.
a)the expected value of R1+R2 for the circuit if the resistance of the line, neutral and cpc loops are 0.2ohms, 0.2ohms and 0.33 ohms respectively. (2 Mark)
b)The effect on the circuit R1+R2 value if a non fused spur supplying a socket-outlet was added to the circuit (1 Mark)

A8.
a)R1+R2 = (r1+r2)/4 = (0.2+0.33)/4 = 0.13
b)It would increase R1+R2 as the cabling supplying the spur would be added.

Q9. Following repairs to a motor and before its reconnection, an insulation resistance test is to be carried out on a securely isolated three phase motor circuit. State
a)The two tests to be carried out in order to complete the schedule of test results in BS7671
(2 Marks)
b)How the cable between the motor starter and the motor maybe included in the test in a)
(1 Marks)

A9.
a)Between live conductors (Live/Live) and between Live conductors and Earth (Live/Earth)
b)Link across the motor starter

Q10. An insulation resistance test is to be carried out to confirm electrical separation of one circuit from another circuit contained in the same conduit. State
a)test connections required to confirm electrical separation (2 Marks)
b)minimum acceptable value of insulation resistance (1 Mark)

A10.
a) Between separated circuit conductors connected together and other circuit conductors connected together. Between separated circuit conductors and earth
b) Tested at 500V DC and greater than 1Mohm
Q11. State three methods of providing protection against electric shock for a 16A socket-outlet circuit installed on a construction site (3 Marks)
A11.
.Insulation of live parts
.Automatic disconnection of supply
.Additional protection via a 30mA residual current device

Q12. State the IP codes for enclosures that provide protection against a
a)12.5mm diameter sphere (1 Mark)
b)British standard finger test only (1Mark)
c)1mm Diameter wire (1 Mark)

A12.
a)IP2X
b)IPXXB
c)IP4X

Q13. State the test carried out to confirm that
a)the outer screw contact of an Edison screw type lamp holder is connected to the neutral conductor (1 Mark)
b)a lighting circuit protective device will disconnect within 0.4s in the event of an earth fault
(1 Mark)
c)a fuse protecting an electrical installation will operate safely in the event of a short circuit fault
(1 Mark)

A13.
a)Polarity test
b)Earth fault loop impedance
c)Prospective fault current

Q14. A test is to be carried out on a earth electrode, using an earth electrode resistance tester. State
a)Why it is necessary to take readings with the centre electrode in three different positions (1 Mark)
b)How to determine the electrode resistance if the three readings in a) above are similar in value
(1 Mark)
c)Another type of test instrument that may be used to carry out this test when the electrode being tested forms part of a TT system and is protected by an RCD (1 Mark)

A14.
a)To ensure the resistance area doesn’t overlap
b)Take the mean of the three readings
c)Earth fault loop impedance tester

Q15. State, for each of the following, the type of system used for public supplies thathas an earth return path, external to the installation consisting of,
a)a PEN conductor (1 Mark)
b)the general mass of earth (1 Mark)
c)separate neutral and protective conductors (1 Mark)

A15.
a) TN-CS
b) TT
c) TN-S

Q16. An earth loop impedance test is to be carried out on a healthy ring final circuit consisting of nine socket-outlets connected directly in the ring. State the,
a)instrument to be used (1 Mark)
b)pattern of test results when carrying out the test at each socket outlet around the ring (1 Mark)
c)value to be recorded on the schedule of test results (1 Mark)

A16.
a)Earth loop impedance tester
b)Should increase slightly as you move closer to the middle of the ring and then decrease again
c)The highest reading taken

Q17. State,
a)one condition where BS7671 requires a 30mA RCD to provide additional protection to a circuit in a office (1 Mark)
b)the maximum permitted disconnection time of the RCD in a) above, when a current of 150mA flows to earth (1 Mark)
c)The maximum permitted earth loop impedance of a circuit forming part of a TT system if it is protected by a 300mA RCD (1 Mark)

A17.
a) Any socket outlet up to 20A that may be used by ordinary persons for general use
b) 40ms
c) Ra = 50/300mA = 167ohms

Q18. State the,
a)effect on the value of prospective fault current when it is measured within the installation at increasing distances from the origin (1 Mark)
b)two types of fault that must be considered on a single phase TN-S system when considering an installation PFC. (2 Mark)

A18.
a)It will decrease
b)Prospective earth fault current and Prospective short circuit current

Q19. State three factors that may affect the measured earth fault loop impedance value of a circuit, excluding final circuit conductor length and cross sectional area. (3 Mark)

A19.
.Ambient temperature
.Electrical Loading
.Being surrounded by insulation

Q20. State the maximum permitted percentage voltage drop for each of the following circuits supplied directly from a public low voltage distribution system.
a)230V lighting circuit (1 Mark)
b)Three-phase 400V motor circuit (1 Mark)
c)Distribution circuit supplying a single phase distribution board (1 Mark)

A20.
a)3%
b)5%
c)5%

The only thing I think im not sure about is in question 10 would you include a test between the separated circuits exposed conductive parts and the cpcs and exposed conductive parts of other circuit?

Thanks

r10ley

 

[Deleted member 26818]

Question 6,a) is incorrect.
You are testing the continuity of protective conductors, it is the live conductors where polarity must be confirmed, the clue, is that in question b), you are adding the recorded measured value from a) to Ze.
Question 17,a) Is also incorrect.
There is no requirement in BS7671 for an office circuit to be RCD protected, unless the office is in or forms part of a special location.
The requirement to RCD protect any socket-outlet intended for general use by ordinary persons, applies only to the socket-outlets, not to the circuit supplying them.
Question 19,c), I doubt the pressence of thermal insulation, will affect the measured value.
Question 10, I would only test between the Live conductors of one circuit, and those of the other to prove separation.

 

[r10ley]

Thanks for your feed back reading 6 a) I can see my mistake need to read question a bit more carefully. As for 17 a) can you help me with the answer im struggling : (

Thanks

r10ley

 

[kennydeeee]

17A sockets for use by unskilled persons in office could be cleaners sockets
or cables concealed in wall less than 50mm deep

 

[Deleted member 26818]

17A sockets for use by unskilled persons in office could be cleaners sockets
or cables concealed in wall less than 50mm deep

The question asks for "one condition where BS7671 requires a 30mA RCD to provide additional protection to a circuit in a office".
Neither of the above applies to circuits whether they be in an office or otherwise.
The only situation where 30mA RCD protection for circuits is required by BS7671 is in relation to special locations.
As such the answer should be when the office is part of an installation on agricultural/horticultural premises, or is itself a transportable unit, such as a portacabin.

 

[r10ley]

Thanks again makes sense, can you help me with this one im not sure about my answers.

Q. Four operational considerations relating to a electrical installation that must be discussed in order to agree the limitations and plan the work. (8 Marks)

A.
. When each part of the installation can be isolated
. Any items of equipment which cannot be disconnected/linked out
. When it is safe to perform certain testing as not to present danger to people
. What percentage of the installation the client would like to be inspected

Thanks

r10ley

 

[kennydeeee]

The question asks for "one condition where BS7671 requires a 30mA RCD to provide additional protection to a circuit in a office".
Neither of the above applies to circuits whether they be in an office or otherwise.
The only situation where 30mA RCD protection for circuits is required by BS7671 is in relation to special locations.
As such the answer should be when the office is part of an installation on agricultural/horticultural premises, or is itself a transportable unit, such as a portacabin.

Im sure u will find in bs7671 2008 the definition of a circuit and a socket outlet would be classed as part of the circuit not just the cable supplying it.

If for example the sockets where for use by the unskilled person additional protection would be required 30 mA rcd to the nessesary part of the circuit in this case the sockets. If the circuit meets
reg 522.6.6 - 522.6.8 then the socket outlets could be 30mA socket outlets if not the rcd would need to be at the origan of the circuit at (dist board)

circuit (assembly of electrical equipment)

As for cables burried in walls in office or anywhere else not under the supervison of a skilled person reg 522.6.6 - 522.6.8

so either 1 of these would be suitable answers

 

[Deleted member 26818]

In this respect, the Regulations are unusually quite precise.
Despite the fact that both socket-outlets and cables are parts that would go towards making up a circuit, there is no requirement in BS7671 for the whole circuit to be RCD protected when these parts require RCD protection.
The question is in relation to a circuit in an office, part of an installation where BS7671 would not normally expect ordinary persons to have access to any socket-outlets, and would expect the installation to be under the control of a skilled or instructed person, as such there would not normally be a requirement for RCD protection, unless a socket-outlet is used to power mobile equipment outdoors, and even then such would not require the whole circuit to be RCD protected.
The only references in BS7671 to circuits requiring RCD protection are in relation to special locations.
You would not normally expect there to be a bath or a shower in an office, so the only special locations that would be applicable to my mind would be those for agricultural/horticultural or transportable units.

 

[topquark]

Regulation 522.6.7 applies as a follow on from 522.6.6. A cable concealed in a wall or partition at a depth of less than 50 mm from a surface of the wall or partition.

 

[kennydeeee]

In this respect, the Regulations are unusually quite precise.
Despite the fact that both socket-outlets and cables are parts that would go towards making up a circuit, there is no requirement in BS7671 for the whole circuit to be RCD protected when these parts require RCD protection.
The question is in relation to a circuit in an office, part of an installation where BS7671 would not normally expect ordinary persons to have access to any socket-outlets, and would expect the installation to be under the control of a skilled or instructed person, as such there would not normally be a requirement for RCD protection, unless a socket-outlet is used to power mobile equipment outdoors, and even then such would not require the whole circuit to be RCD protected.
The only references in BS7671 to circuits requiring RCD protection are in relation to special locations.
You would not normally expect there to be a bath or a shower in an office, so the only special locations that would be applicable to my mind would be those for agricultural/horticultural or transportable units.

as i said cleaners sockets in an office for general purpose a cleaner would not be a skilled person the cleaner would be hovering after hours so would not be under any supervision from a skilled person so the sockets would would require additional protection.



I dont really care anymore i done this paper as a mock exam got this question marked right and got 90%

 

[Deleted member 26818]

as i said cleaners sockets in an office for general purpose a cleaner would not be a skilled person the cleaner would be hovering after hours so would not be under any supervision from a skilled person so the sockets would would require additional protection.

I dont really care anymore i done this paper as a mock exam got this question marked right and got 90%

There are exceptions for some of the Regulations requiring RCD protection in BS7671. Primarily these exceptions apply to commercial/industrial installations where the Electricity At Work Regulations apply.
Here is the entirity of Regulation 16 of EAWR 1989 "No person shall be engaged in any work activity where technical knowledge or experience is necessary to prevent danger or, where appropriate, injury, unless he possesses such knowledge or experience, or is under such degree of supervision as may be appropriate having regard to the nature of the work."
This Statutory requirement, entails that anyone (including cleaners) using a socket-outlet as part of their work duties must meet the criteria for a skilled or instructed person as defined in BS7671.
As such there is no requirement in BS7671 for cleaner sockets to be RCD protected, unless that socket-outlet is used for mobile equipment outdoors, or is in a special location
Now I don't know who marked your mock exam, or what answer you gave for this particular question.
I doubt though from the information you have supplied, that if you had taken the December 2010 exam, that you would have got this question marked as correct.

 

[Flakey]

Hi i was looking at this old post and saw a calculation resolved which im not too sure is right and would apprciate confirmation wether it is or isnt
Q24. A continuity of ring final circuit conductors test is to be carried out on a circuit supplying the office. The circuit is wired in 2.5mm cable with 1.5mm cpc. The loop length of the cable is 65m. All socket outlets are connected directly on the ring. Explain in detail, using the information given in figure 1, the three steps required to confirm the continuity of this circuit.
Your explanation should include the
. test instrument
. test connections and the expected readings at each stage
Show all calculations

A24. The test instrument used is a low resistance ohm meter. First test is an end to end of the line neutral and cpc of the ring. This is confirm all conductors form a complete ring. The expected results are:

Line – line – 2.5mm cable = 7.41 mohm/m
(7.41x65)/1000 = 0.48 ohms

Neutral – Neutral – Same as above

Cpc – Cpc – 1.5mm = 12.1 mohms/m
(12.1x65)/1000 = 0.786 ohms

Next cross connect line and neutral of the ring L1 + N2 and L2 +N1 and test at all socket outlets
Expected readings:

R1+Rn = (r1+rn)/4 = (0.48+0.48)/4 = (0.24) ohm Do you use this figure in the stage 3 part of the calculation

Next cross connect line and cpc L1 + cpc2 and L2 + cpc1 and test at all socket outlets
Expected readings:

R1+R2 = (r1+r2)/4 = (0.48+0.786)/4 = 0.32 ohms so 0.24 + 0.786/4 = 0.25 ohm ?

Many thanks
James