***Useful Information for Apprentices***

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[FONT=IIFPD I+ Gill Sans]RCDs for protecting people have a rated tripping current (sensitivity) of not more than 30 milliamps (mA). Remember: [/FONT]
* an RCD is a valuable safety device,
* if the RCD trips, it is a sign there is a fault. Check the system before using it again;
* if the RCD trips frequently and no fault can be found in the system, consult the manufacturer of the RCD;
* the RCD has a test button to check that its mechanism is free and functioning. Use this regularly.

;) Use of 110V or 230V Equipment and Supplies : Q/A .

For Many Years , the Use of 110V CTE , ( Centre Tap Earthed ) has been Encouraged in Harsh Environments such as Construction Sites , This was Largely a UK Initiative , but in the rest of Europe , Systems of Working with 230V have been Established . if Responsible Individuals decide to Stipulate that Reduced Voltage is to be Used it must be made Clear that the Requirement is Dependant on the Environment and is therefore a Site Decision , the Use of 110V CTE , and Other Low-Voltage Systems in the UK is NOT Compulsory Under the Law but has been Recognised as Good-Practice in Harsh Environments , Guidance on Reduced Low Voltage Systems and Extra Low Voltage Systems is Provided in BS-7671
 
;) The Regulations affecting RCD protection
Rule 411.3.3
Additional protection by means of a 30mA RCD is to be provided for all socket outlets with a rated current not exceeding 20A for use by ordinary persons. The only exceptions allowed are for socket outlets for use under the supervision of ‘skilled’ or ‘instructed persons’ e.g. some commercial/industrial locations, or a specifically labelled socket provided for connection of a particular item of equipment, such as a freezer.

Rule 710.411.3.3
In specific locations such as those containing a bath or shower there is now a requirement to provide RCD protection on all circuits, including lighting and shower circuits.

Rule 314.1 & 2
Every installation should be provided into circuits as necessary to avoid danger and minimise inconvenience in the event of a fault. Designers are required to reduce the possibility of unwanted RCD tripping due to excessive protective conductor currents but not due to an earth fault.
Separate circuits may be required for parts of the installation which need to be separately controlled in such a way that they are not affected by the failure of other circuits. The appropriate subdivision should take account of any danger arising from the failure of a single circuit, for example and RCD trip causing the disconnection of an important lighting circuit.

Regulation 522.6.7
Much greater use of RCDs is required to protect wiring concealed in walls or partitions, even where this is installed in previously defined Safe Zones.
This effectively means that all concealed wiring at a depth of less than 50mm from the surface now requires protection by a 30mA RCD unless provided with earthed mechanical protection.
 
;) HSE Guidance
To comply with Regulation 13 of the Electricity at Work Regulations, precautions need to be taken on equipment that has been made dead. this includes securing the means of disconnection in the OFF position, putting a notice or label at the point of disconnection, and proving dead at the point of work using proprietary voltage detectors.

To comply with Regulation 14 of the Electricity at Work Regulations, dead working should be the normal method of carrying out work on electrical equipment or circuits. Live working should only be carried out in particular circumstances where it is unreasonable to work dead, such as some fault finding and testing, where the risks are acceptable, and where suitable precautions can be taken against injury. The pressure to carry out live work is becoming more common in areas such as construction sites, high-cost manufacturing and in retail outlets operating twenty-four hours per day. The requirements of the Regulations still apply in such situations and live working should only be carried out when justified using the criteria explained

Proving Dead Isolated Equipment or Circuits
Following isolation of equipment or circuits and “ BEFORE “ starting work it should be “ PROVED “ that the parts to be worked on and those nearby, are dead. It should “ NEVER BE ASSUMED “ that equipment is “ DEAD “ because a particular isolation device has been placed in the off position.

The procedure for proving dead should be by use of a proprietary test lamp or two pole voltage detector as recommended in HSE Guidance Note GS38, Electrical test equipment for use by electricians. Non-contact voltage indicators ( VOLTAGE STICKS) and “ MULTI-METERS “ should “ NOT BE USED “ . The test instrument should be proved to be working on a known live source or proprietary proving unit before and after use. All PHASES of the SUPPLY and the NEUTRAL should be tested and proved dead.

Safe Systems of Work
The employer must ensure that all employees involved in work on electrical equipment are competent and are instructed on safe systems of work, have been issued with written rules and instructions, and have access to, and use, appropriate locking-off devices, caution notices, a proprietary voltage detector and, where appropriate for the type of voltage detector being used, a proving unit.
 
;) Type of Electrical Circuits :-
There are three main types of circuits encountered in a domestic situation. They are Ring Circuits, Radial Circuits and Lighting Circuits.
 
;) * Electric Shock Occurs when a Person become Part of the Electrical Circuit :

To Prevent People Receiving an Electric Shock Accidentally , all Circuits must contain Protective Devices and all Exposed Metal must be Earthed ,
- All Circuits must be Electrically Isolated before any Work is Carried Out ,
- Electrical Isolation is an Important Safety Procedure ,
* the IEE Regulations tell us that Every Circuit must be Provided with Means of Isolation ,
* the Electricity at Work Regulations tell us that before Work Commences on Electrical Equipment it must be Disconnected from the Source of Supply and that the Disconnection must be Secure ,

Three-Effects of an Electric Current :-
When an Electric Current flows in a Circuit it can have One or More of the following Three-Effects : Heating : Magnetic or Chemical
* Heating Effect :-
* The Electrons moving in the Conductor causes the Conductor to Heat Up
* The Amount of Heat Generated depends upon the :
1) Amount of Current Flowing ,
2) Dimensions of the Conductors ,
3) Type of Conductor Material Used ,

* Practical Applications of the Heating Effect of an Electric Current are :-
1) Radiant Heaters which Heat Rooms ,
2) Circuit Protection Fuse and MCBs which Cut off the Supply when an Overcurrent Flows ,

Magnetic Effect :-
* Whenever a Current Flows in a Conductor a Magnetic Field is Set Up around the Conductor like an Extension of the Insulation ,
* Increasing the Current Increases the Magnetic Field ,
* Switch the Current off Causes the Magnetic Field to Collapse ,
* Practical Applications of the Magnetic Effect are :-
1) Electric Motors which Rotate because of the Magnetic Flux Generated by the Electrical Supply door Chimes and Buzzers which ding dong or buzz because of the Magnetic Flux Generated by the Electrical Supply ,

Chemical Effect :-
* When an Electric Current Flows though a Conducting Liquid , the Liquid Separates into its Chemical Parts , a Process called Electrolysis ,
* Alternatively , if two Metals are Placed in a Conducing Liquid they React Chemically and Produce a Voltage ,
* Practical Applications of the Chemical Effect are :-
1) Industrial Processes such as Electroplating which is Used to Silver Plate Sports Trophies and Cutlery ,
2) Motor Car Batteries which Store Electrical Energy ,

Three-6Ω Resistors are Connected in Series :- ( for any Series Connection )
Resistors in Series , Rt = R1 + R2 + R3 ,
Rt = 6Ω + 6Ω + 6Ω = 18Ω
Total Current It = Vt – Rt
Therefore :- It = 12V - 18Ω = 0.67A

The Voltage Drop across ( R1 is )
V1 = It x R1
Therefore :- V1 = 0.67A x 6Ω = 4V
The Voltage Drop across ( R2 is )
V2 = It x R2
Therefore :- V2 = 0.67A x 6Ω = 4V
The Voltage Drop across ( R3 is )
V3 = It x R3
Therefore :- V3 = 0.67A x 6Ω = 4V
I1 / R1 - 6Ω
I2 / R2 - 6Ω
I3 / R3 - 6Ω
It ( Vt = 12V )
 
Resistors in Parallel :-
For any Parallel Connection , ( 1/Rt = 1/R1 + 1/R2 + 1/R3 )
Therefore :- 1/Rt = 1/6Ω + 1/6Ω + 1/6Ω

1/Rt = 1 + 1 + 1 = 3… 6Ω
Rt = 6Ω ÷ 3 = 2Ω
Total Current It = Vt/Rt , therefore :- It = 12V ÷ 2Ω = 6A
The Current flowing through ( R1 is )
I1 = Vt/R1 , therefore :- I1 = 12V ÷ 6Ω = 2A
The Current flowing through ( R2 is )
I2 = Vt/R2 , therefore :- I2 = 12V ÷ 6Ω = 2A
The Current flowing through ( R3 is )
I3 = Vt/R3 , therefore :- I3 = 12V ÷ 6Ω = 2A

Component Parts of an Electrical Circuit :-

These Series and Parallel Resistors are Connected together to form an Electrical Circuit , so , what is an Electrical Circuit ?
An Electrical Circuit has the following Five Components :-
* a Source of Electrical Energy , this might be a Battery giving a D.C. ( direct current ) Supply or the Main Supply which is A.C. ( alternating current )
* a Source of Circuit Protection , this might be a Fuse or Circuit-Breaker which will Protect the Circuit from “ Overcurrent “
* the Circuit Conductors or Cables . these carry Voltage and Current to Power the Load ,
* a Means to Control the Circuit , this might be a simple On/Off Switch but it might also be a Dimmer or a Thermostat ,
* and a Load , this is Something which needs Electricity to make it Work , it might be a Electric Lamp , an Electrical Appliance , an Electric Motor or an i-pod
 
A Transformer Feeds the 9.81kW Motor Driving the Mechanical Hoist , the Input Power to the Transformer was found to be 10.9kW
Find the Efficiency of the Transformer :- ?? ŋ = Power Out / Power Input x 100 ( ŋ = 9.81kW / 10.9kW x 100 = 90% )

Thus the Transformer is 90% Efficient ,
Note : that Efficiency has No Units , but is Simply Expressed as a Percentage ,

Electrical Transformers :-
A Transformer is an Electrical Machine without Moving Parts , which is Used to Change the Value of an Alternating Voltage ,
- a Transformer will Only Work on an Alternating Supply . it will NOT Normally Work from a D.C. Supply such as a Battery ,

Transformer : Consists of Two-Coils called the ( Primary and Secondary ) Coils or Windings , wound on to a Common Core , the Iron Core of the * * *Transformer is NOT Solid but Made Up of very Thin Sheets called ( Laminations ) to Improve Efficiency ,
* an Alternating Voltage Applied to the Primary Winding Establishes an Alternating Magnetic Flux in the Core ,
* the Magnetic Flux in the Core causes a Voltage to be Induced in the Secondary Winding of the Transformers ,
* the Voltage in both the ( Primary and Secondary ) Windings is Proportional to the Number of Turns ,
* this Means that if you Increase the Number of Secondary Turns you will Increase the Output Voltage , this has an Application in Power Distribution ,
* Alternatively , Reducing the Number of Secondary Turns will Reduce the Output Voltage , this is Useful for ( Low-Voltage-Supplies ) such as Domestic bell Transformers’ , because it has NO Moving Parts , a Transformer can have a Very High Efficiency , Large Power Transformers , Used on
Electrical Distribution Systems , can have an Efficiency of Better than 90% ,

These Power Transformers need ( Cooling ) to take the ( Heat ) Generated away from the ( Core ) this is Often Achieved by Totally Immersing the Core and Windings in Insulating ( Oil )

Very Small Transformers are Used in Electronic Applications , Small Transformers are Used as Isolating Transformers in ( Shaver Sockets ) and can be Used to Supply ( SELV ) separated extra low voltage , Sources , Equipment Supplied from a SELV Source may be Installed in a Bathroom or Shower room , Provided that it is Suitably Enclosed and Protected from the ( Ingress of Moisture ) this includes Equipment such as Water Heater , Pumps for Showers and Whirlpools Baths ,
 
;) Q : What is the Voltage of the Neutral Terminal ?
A : it stays as a Potential Close to Zero with Respect to Earth ,

Q : What should be done to Appliances with Metal Cases ?
A : They are Usually Earthed ,

Q : Describe how the Résistance of a Thermistor changes as the Temperature Increases ?
A : it Decreases ,

Q : For Components Connected in Series , what do you know about the Total Potential Difference ?
A : The Potential Difference of the Supply is Shared between the Components According to their Résistance – Bigger Résistance – Bigger Share ,

Q : What is the Voltage of the Live Terminal ?
A : The Live Terminal of the Mains Supply Alternates between Positive and Negative Potential with Respect to the Neutral Terminal ,

Q : For Components Connected in Parallel , what do you know about the Current Through Them ?
A : The Total Current through the Whole Circuit is Equal to the Sum of the Currents through the Separate Components – and the Lower the Résistance if the Component , the More the Current Flows ,

Q ; For Components Connected in Parallel , what do you know about the Potential Difference Across each Component ?
A : it is the Same ,

Q :What Type of Current do Cells and Batteries Supply ?
A : Direct Current ( d.c. )

Q : for Components Connected in Series , what do you know about the Current through each Component ?
A : it is the Same ,

Q : for Components Connected in Series , how do you Calculate the Total Résistance ?
A : The Total Résistance is the Sum of the Résistance of Each Component ,

Q : How do you know what Value of Fuse to put in an Appliance’s Plug ?
A : From the Power and the Voltage we can Calculate the Current and the Fuse it Needs ,

Q : What is Résistance ?
A : The Ratio of Potential Difference across a Component to the Current Flowing through it ,

Q : What happens when an Electrical Charge Flows through a Resistor ?
A : Electrical Energy is Transformed into Heat Energy ( it get Hot )

Q : What does the Size of the Current in a Circuit Depend on ?
A : How hard the Supply tries to Push Charge through the Circuit and how hard the Circuit Resists having Charge Pushed through it ,

Circuit Basics :-
All Electrical Circuits Require three-Elements ,
1) A Source Voltage , that is , an Electron Pump usually a Battery or Power Supply , ( Energy In )
2) A Conductor to Carry Electrons from and to the Voltage Source ( Pump ) the Conductor is often a Wire , ( Energy Transfer )
3) A load or Résistance , A Point where Energy is Extracted form the Circuit in the Form of Heat , Light , Motion , etc. ( Energy Out )

Potential Changes of Current in a Circuit :-
High Energy Current ► Résistance ( Potential Drop ) Low Energy Current ► ,
High Energy Current ◄ Voltage Source ( Potential Rise ) Low Energy Current ◄

Measureable Quantities that can be Obtained from an Electrical Circuit :-
1) Voltage Rise – Measures the Energy given to Electrons as they leave a Voltage Source , it is Measured in Volts ( + )
2) Voltage Drop - Measures the Energy lost by to Electrons when they leave a Résistance , it is Measured in Volts ( - )
3) Current - Measures the Flow Rate through a Conductor , it is Measured in Amperes ( AMPS )
4) Résistance - Measures the Opposition to Current Flow through a Conductor or Resistor , it is Measured in Ohms ( its Symbol . is Omega )

Voltage Sources and Internal Resistance :-
1) All Voltage Sources contain Internal Résistance , that is Resistance that is Part of the Voltage Producing Device itself which cannot be Eliminated ,
2) The Voltage that the Device ( Battery for Example ) could Produce if no Internal Résistance was Present is called its ( EMF ) stands for Electromotive Force – the Force that moves the Electrons ,
3) The Useable Voltage which is Available to the Circuit after the Internal Résistance Consumes its Share of the ( EMF ) is Called the Terminal Voltage ,
 
;) Q: What are the advantages of star-delta starter with induction motor ?
A 1). The main advantage of using the star delta starter is reduction of current during the starting of the motor. Starting current is reduced to 3-4 times Of current of Direct online starting.(2). Hence the starting current is reduced , the voltage drops during the starting of motor in systems are reduced.
 
Ohm's Law

To make a current flow through a resistance there must be a voltage across that resistance. Ohm's Law shows the relationship between the voltage (V), current (I) and resistance (R). It can be written in three ways:

V= I x R or I = V / R or R = V/I

Where :-

V = voltage in volts (V)
I = current in amps (A)
R = resistance in ohms ( ) or :-

V = voltage in volts (V)
I = current in milliamps ( mA)
R = resistance in kilohms (k )
For most electronic circuits the amp is too large and the ohm is too small, so we often measure current in milliamps (mA) and resistance in kilohms (k ). 1 mA = 0.001 A and 1 k = 1000 .
The Ohm's Law equations work if you use V, A and , or if you use V, mA and k . You must not mix these sets of units in the equations so you may need to convert between mA and A or k and .
You can use the VIR triangle to help you remember the three versions of Ohm's Law. Write down V, I and R in a triangle ,

* To calculate voltage, V: put your finger over V, this leaves you with I R, so the equation is ( V = I × R ) * To calculate current, I: put your finger over I, this leaves you with V over R, so the equation is ( I = V/R ) * To calculate resistance, R: put your finger over R, this leaves you with V over I, so the equation is ( R = V/I )


Ohm's Law
Use this method to guide you through calculations: 1) Write down the Values, converting units if necessary. 2) Select the Equation you need (use the VIR triangle). 3) Put the Numbers into the equation and calculate the answer.
It should be Very Easy Now! 3 V is applied across a 6 resistor, what is the current ? * Values: V = 3 V, I = ?, R = 6 * Equation: I = V/R Numbers: Current, I = 3/6 = 0.5 A
* A lamp connected to a 6 V battery passes a current of 60 mA, what is the lamp's resistance? * Values: V = 6 V, I = 60 mA, R = ? * Equation: R = V/I * Numbers: Resistance, R = 6/60 = 0.1 k = 100 * using mA for current means the calculation gives the resistance in k )
* A 1.2 k resistor passes a current of 0.2 A, what is the voltage across it? Values: V = ?, I = 0.2 A, R = 1.2 k = 1200 (1.2 k is converted to 1200 because A and k must not be used together) * Equation: V = I × R * Numbers: V = 0.2 × 1200 = 240 V
 
:rolleyes: Insulation Résistance :- Regs , table 61 – p/158 ,

The Insulation Résistance Test is also known as a ( Megger Test ) it Objective is to Measure the Total Résistance between Two-Points Separated by Insulation , the Test , therefore , Determines how Effective the Insulation is in the Flow of Electrical Current , the Voltage is Typically around 500V-1000V d.c. Hence , the Current is Very Low , because the Current is Low , this Test is Useful for Checking the Quality of the Insulation not Only when a Product is First Manufactured , but also Over-Time as the Product is Used ,
 
;) It's Resistivity, not Resistance :-

The problem with using resistance as a measurement is that it depends not only on the material out of which the wire is made, but also the geometry of the wire. If we were to increase the length of wire , for example, the measured resistance would increase. Also, if we were to decrease the diameter of the wire, the measured resistance would increase. We want to define a property that describes a material's ability to transmit electrical current that is independent of the geometrical factors.

In the case of the wire, resistivity is defined as the resistance in the wire, multiplied by the cross-sectional area of the wire, divided by the length of the wire. The units associated with resistivity are thus ohm.m (ohm - meters).

Resistivity is a fundamental parameter of the material making up the wire that describes how easily the wire can transmit an electrical current. High values of resistivity imply that the material making up the wire is very resistant to the flow of electricity. Low values of resistivity imply that the material making up the wire transmits electrical current very easily.
 
;) The Resistance of a Wire

Aim: To find out what happens to the resistance of a wire when you change its length.
PLANNING

Resistance is something that opposes or slows something or an object down, in electricity it means the same the current in the wire is slowed down by the atoms that make up the wire. So what happens if we change the length?

the flow of electrons through a wire. The electrons have to get past all the atoms that are constantly moving around the wire, to reach the end of the wire. The atoms slow the electrons down considerably, this is known as "resistance."

The scientific theory is that if you increase the length of the wire the resistance will rise and if you decrease the length the resistance will fall

The Variables The resistance of the wire can be affected/changed, by varying many variables, these include :-

* Length of Wire * Width/Thickness of wire * Type of Wire * Temperature

The length of wire affects the resistance because there are more atoms present in the wire and using scientific knowledge I know that the resistance should increase because there are more obstacles for the electrons to pass.

The width/thickness of wire can change the resistance because if the width of the wire increases the resistance decreases because there is more space for the electrons to pass the atoms. It won't be as compact as usual.

The type of wire can affect the resistance, because each type of wire contains different amount of atoms and if you use different types of wires .

The temperature is a major factor of affecting the resistance as the resistance will decrease if the temperature becomes to hot, because the temperature varies.

* There is a relationship between the voltage and the current because if you increase the voltage, you also increase the current another relationship is between the current and the resistance if you increase the resistance the current decreases.

:rolleyes: Ohm's law is only true if the temperature remains constant, because the atoms in the wire start to vibrate as they become warmer, which causes more movement and even more resistance.
 
;) Cable has Solid Cores ( Conductors’ ) and thus Doesn’t Bend Easily ( i.e. it isn’t a Flexible Cord ) it is Used in Places where it won’t be Moved Once it is Installed ,
 
;) What is the Basic Unit of Electrical Power : > Power , Expressed in Watts = Voltage , in Volts , Times Current , in Amperes , P = E / I → Watts = Volts * Amperes .


Q) How fast does each one make the Electrical Utility Meter on the Side of your House Spin ? The 100 Watt Bulb
A) The Device with the Highest Wattage Spins it the Fastest ,

Q) what is the Word Used to Describe how Fast Electrical Energy is Used ? Power
A) the Watt is the Unit Used to Measure the Rate of Energy Use ,

Q) Which of the Following Two Quantities should be Multiplied together to find Power ? Voltage and Current
Q) Which Two Electrical Units Multiplied together give the Unit “ Watts “ ? Volt and Amperes

Q) a Resistor in a Circuit becomes Very Hot and Starts to Burn , this is Because the Resistor is Dissipating to Much ? Power
Q) if a Current of 2 Amperes flows through a 50 Ohm Resistor , what is the Voltage Across the Resistor ? 50Ω x 2 Amperes = 100 Volts
Q) how is the Current in a D.C. Circuit Calculated when the Voltage and Résistance are Known ? A) Current Equals Voltage Divided by Résistance ,
Q) how is the Résistance in a D.C. Circuit Calculated when the Voltage and Current are Known ? A) Résistance Equals Voltage Divided by Current ,
Q) how is the Voltage in a D.C. Circuit Calculated when the Current are Résistance are Known ? A) Voltage Equals Current Multiplied by Résistance ,

Q) if a 12 Volt Battery Supplies 0.25Ampere to a Circuit , what is the Circuit’s Résistance ? A) > Ohms Law ( I = E/R ) becomes ( R = E/I ) when Solving for ( R ) Résistance is Voltage Divided by Current , Ohms = Volts / Amperes , 12 Volts ÷ 0.25 Amperes = 48Ohms ,

Q) what Voltage would be Needed to Supply a Current of 20mA to Operate an Electric Lamp which has a Résistance of 25Ohms ? A) > Ohms Law ( I = E/R ) becomes ( E = R*I ) when Solving for ( E ) Voltage is Résistance times Current , Volts = Ohms * Amperes , 25Ω x 0.200Amperes = 5 Volts

Q) if a 3 Volt Battery Supplies 300mA to a Circuit , the Circuit Résistance is ? A) > Ohms Law ( I = E/R ) becomes ( R = E/I when Solving for ( R ) Résistance is Voltage Divided by Current , ( Ohms = Volts / Amperes ) 3V ÷ 0.300A = 10Ω ,

Q) Why would a Large Size Resistor be Used instead of a Smaller one of the Same Résistance ? A) > Remember that Power is Voltage times Current , ( P = E*I ) a Resistor Dissipates Power into Heat , a Resistor can Only Dissipate so much Power without Burning Up , i.e. its Power Rating , Larger Resistors can Dissipate more Heat ,

Q) Resistor Wattage Ratings are ?
1) Calculated According to Physical Size ,
2) Expressed in Joules per Second ,
3) Determined by Heat Dissipation Qualities , ***
4) Variable in Step of one Hundred ,

> Materials , Shape , Construction all interact to Determine Heat Dissipation Capabilities ,
A) 1 Might be a Distant Second Best ,
( Choice !! 1 in the French Question Bank includes an Allusion to Tolerance , Obviously False )
 
;) Testing :- Three-Phase ,

Line to Line = 400V or alternatively L1-L2, L1-L3, L2-L3 = 400V
Line to Neutral = 230V or alternatively L1-N, L2-N, L3-N = 230V
Line to Earth = 230V or alternatively L1-E, L2-E, L3-E = 230V
Neutral to Earth = 0 V
 
;) Electrical Fundamentals :
Q) the particles that orbit around the centre of an atom are ?
A) - Electrons , ◄
Molecules ,
Nucleus ,
Protons ,
- Electrons orbit around the nucleus of an atom ,
Q) an atom which loses or gains one electron is called ?
A) a charged particle or ion , ◄
Balanced ,
An Element ,
A Molecule ,
- Ions are charged particles either positive or negative , atoms that looses an electron becomes a positive ion and an atom that gains an electron becomes a negative ion ,
Q) the conventional theory of current flow says that current flows ?
A) Positive to Negative , ◄
Randomly ,
Negative to Positive ,
None of the above ,
- conventional or hole theory states that current flows from Positive to Negative ,
Q) the force that causes electrons to flow through a conductor is known as ?
A) the Voltage , ◄
The Power ,
The Current ,
The Résistance ,
- Voltage is the force that pushes electrons through a conductor , Voltage is electrical pressure also known as ElectoMotive Force ( EMF )
Q) two identical lamps are connected in Parallel to a 12 Volt source , the voltage across each lamp is ?
A) 12 Volts , ◄
6 Volts ,
4 Volts ,
2 Volts ,
- each branch of a Parallel Circuit receives the source voltage of 12 Volts ,
Q) in a Parallel Circuit which of the following is True ?
A) Circuit Résistance Decreases as Additional Circuits are Added , ◄
Current is equal in all parts of the circuit ,
Only one current path to ground
None of these ,
- by Adding Additional Paths to Ground ( Earth ) Résistance Drops and Current goes Up ,
Q) a Break or Interruption in an electrical circuit is ?
A) an Open , ↔ ( A Break in a Wire is Called an Open ) ◄
a Short ,
a Ground ,
None of the above ,
Q) the sum of voltage drops in a series circuit equals the ?
A) Source Voltage , ◄
Voltage across the largest load ,
Voltage across the smallest load ,
Shunt circuit voltage ,
Q) Electrician A , say circuit protection devices are sensitive to current , Electrician B , say they are sensitive only to voltage , Who is correct ?
A) Electrician A only ◄
Electrician B only ,
Both Electrician A and Electrician B ,
Neither Electrician A nor Electrician B ,
- as current flows through a conductor , it generates heat , when current flow is excessive it melt or opens the protection device ,
Q) the strength of the magnetic field that surrounds a single conductor with current flowing through it ?
A) all of these ◄
Varies directly with the amount of current flowing through the conductor ,
Is usually weak ,
Can be detected using a magnetic compass ,
- magnetic field intensity is weak but varies in size with current strength ,
Q) when the lines of a magnetic field cut across a conductor ?
A) a Voltage is induced into the conductor , ◄
The conductor is permanently induced ,
The conductor is permanently magnetised ,
Magnetism is induced into the conductor ,
- as lines of force cut across the conductor they induce voltage ,

 
Q) when current stops flowing through an inductor ( coil ) such as in a relay ?
A) a voltage spike is generated , ◄
an A.C. signal is produced ,
a magnetic field is developed ,
all of the above ,
- when current stops flowing through a coil , the magnetic field surrounding the coil collapses causing a voltage spike in the opposite polarity to develop , this opposite polarity voltage is known , CEMF , abbr. counter-electromotive force
Q) the three leads of a bipolar transistor are ?
A) the Base , the Collector , and the Emitter , ◄
Q) in this Relay :- ?
A) Terminal 4 is connected to Terminal 5 until energised , then Terminal 4 is connected to Terminal 3 ◄
Terminal 4 is connected to Terminal 3 until energised , then Terminal 4 is connected to Terminal 5
Terminal 3 is connected to Terminal 5 until energised , then Terminal 3 is connected to Terminal 4
Terminal 1 is connected to Terminal 5 until energised , then Terminal 1 is connected to Terminal 4
- when the control coil is energised , the switch connect terminals 4 and 3 together ,
Q) a device that produces a voltage when put under pressure is ?
A) a Crystal , ◄ ( a battery , a generator , a solar cell )
Piezo crystal under pressure will produce a voltage potential ,
Q) when the lines of a magnetic force cut across a conductor ?
A) a voltage is induced into the conductor , ◄
The conductor is permanently induced ,
The conductor is permanently magnetised ,
Magnetism is induced into the conductor .
- Voltage is induce as the flux cuts through a winding ,
Q) when electrical current is passed through a conductor that is forced into many loops , a magnetic field is created , the strength of the field may be increased by ??
A) Both A and B , ◄
Increasing the turns or coils of the conductor ,
Increasing the amount of the current in the coils .
Neither A nor B ,
- increasing the current or the number of turns will strengthen the field ,
 
Push button. :- A normally open push button conducts electricity when it is being pressed, otherwise it's an open circuit.
Switch. :- Has an on and an off position. Conducts when it's on and is an open circuit when off.
 
:rolleyes: Voltage :-
Symbol V or E or U
Unit of Measurement : Volt – Symbol : V ,

Voltage is the Force or Pressure of Electricity , the Higher the Voltage , the Greater the Pressure , Voltage is Often Compared to Water Pressure for Easier Understanding ,

Electricity Loses Pressure because of Résistance to its Flow just as the Flow of Water is Restricted by a Valve or Tap ,

Voltage ( or Pressure ) Drop is Caused by the Work Done ,
The Cumulative Effect of Résistance in Long Wires Creates Résistance to the Flow of Electricity Causing a Drop in Voltage along the Wires Length , a Long Hose has the Same Effect with Water Pressure ,

The Voltage or Pressure of Electricity is Measured by Means of a Voltmeter Connected between the Active Conductor and the Neutral or Earth Conductor , The Voltage Indicates the Amount of Potential Difference between the Two Points it is Applied to , for Example , a Reading taken in this Manner at a Socket Outlet , The Voltmeter would Indicate the Potential Difference to be 230V

The Voltage on a Circuit or Appliance can be Calculated Using Ohms Law or the Power Triangle ,
Ohms Law ,
V = I x R ,

Where :
V = Voltage ,
I = Current .
R = Résistance ,

* Power Triangle :
V = P / I ,

* Where :
P = Power ,
I = Current ,
V = Voltage ,

( Alternatively , the Following Formula can be Used ) V = √ ( P x R ) ,
 
:rolleyes: Current :-

Symbol I
Unit of Measurement : Amp or Ampere – Symbol : A ,

Current is a Measure of the Flow of Electricity through a Conductor Under the Pressure of the Voltage , it can be Compared with the Flow of Water through a Pipe Under Pressure of a Tank or Pump ,

Current is Measured in Amperes ( Amps ) or milliamperes ( mA ) or microamperes ( µA )
* 1 milliamp ( 1 mA ) = 0.001 Amps ( One Thousandth of 1 Amp ) – Note : milli = 10-3 ,
* 1 microamp ( 1 µA ) = 0.000001 Amps ( One millionth of 1 Amp ) – Note : micro = 10-6
* 1 Amp = 1,000 milliamps or 1000 milliamps = 1 Amp
* 1 Amp = 1,000,000 microamps or 1,000,000 microamps = 1 Amp

Current tends to Heat Up the Conductors as it Passes through , the Conductor’s Natural Resistance to the Flow of Current Causes this as the Voltage Pressure Force it through , too much Current will Produce Sufficient Heat to Exceed the Temperature Rating of the Insulation / Damaging it and Causing it to Loose its Insulating Properties ,

If the Temperature become Excessive it may in Time Eventually Melt or Burn Out the Conductor , A Larger Conductor is Required if the Amperage is to be Increased without Increasing the Conductor Temperature ,

The Current in a Circuit or Appliance can be Calculated Using Ohms Law or the Power Triangle

Ohms Law ,
V = I x R ,

Where :
V = Voltage ,
I = Current ,
R = Résistance ,

* Power Triangle :
V = P / I ,

* Where :
P = Power ,
I = Current ,
V = Voltage ,

( Alternatively , the Following Formula can be Used ) I = √ P - R ) ,
 
;) Résistance :-

Symbol R
Unit of Measurement : Ohm – Symbol : Ω ,

Résistance , Expressed in Ohms ( Ω ) is Measure of the Opposition Encountered by the Current Flowing through a Conductor ,

All Conductors Possess some Résistance , its Value Depends Upon the Type of Material Used for the Conductor , its Temperature , its Length and Cross-Sectional Area .
* The Greater the Length – the Greater its Résistance .
* The Greater the Cross-Sectional Area – the Lower its Resistance .

This is Similar to the Résistance Offered to a Flow of Water through a Hosepipe .

Some Materials are Classified as Insulators if they Possess Sufficient Résistance to Restrict Current Flow to Only a Few micro-amps ( 1 Amp = 1,000,000 micro-amp , ( µA ) Under a Pressure of Several Hundred Volts ,

Résistance Equals Voltage Divided by Current Flowing – Ohms Law :
R = V / I

Where R = Résistance ( Ohms )
V = Volts ,
I = Current ( Amps )

e.g. 230V ÷ 10A = 23 Ohms ,

Power :-
Symbol P or W
Unit of Measurement Watt – Symbol W ,

Watts are a Measure of the Consumption of Electricity by the Electrical Appliance ,

The Power Consumed by Lighting or Heating Electrical Appliances can be Calculated using the Power Triangle ,

P = V x I

Where :-
P = Power
I = Current
V = Voltage

Alternatively , The Following Formulae can also be Used ,

P = I2 x R
P = V2 / R

e.g. 230Volts x 10 Amps = 2300 Watts = 2.3 kilowatts – ( Note : kilo = 1,000 or 10-3 )

it follows that for a Constant Voltage System ( e.g. the Standard 230V System Supplied to Domestic Premises ) Current is Directly Proportional to the Wattage of the Electrical Appliance ,

to Calculate the Power Consumed by Single-Phase Electrical Appliances that Contain Electromagnetic Components such as Solenoids or Motors the Following Formula is Used ,

P = V x I x Cos Ø
Cos Ø Means Power Factor ,
 
:eek: Where it is Possible to Touch Conductive Parts , !!!!

It is still Possible to Use Equipment without an Earth Provided it is “ Double Isolated “ which Means there are at Least Two Barriers Between the Incoming Power and Exposed Parts , Equipment Designed this Way Should bear a Symbol which is Two Concentric Squares and it will Normally have been Tested to High Voltage ( > 1.5kV ) to Ensure No Conduction Can Take Place , Usually , the Double Barrier is a Transformer where the Primary and Secondary Windings Share the Same Core but Cannot Come into Contact with Each Other ,
 
:eek: Why an Earth ??

An Earth IS Used wherever there is a Risk of Electric Shock by Direct Connection to Incoming A.C. or by Build Up of Charge through Capacitive Leakage , the Idea is that should a Component Failure Occur or Conductive Path be Made , the Current Will Flow Via Earth Connection and Operate the Safety Trip in the Distribution Board ( MCB ) if the Distribution Board has Earth Leakage Trips , they will Detect the Current and Switch the Power OFF , if it has Balanced Trips , it Will Detect the Line and Neutral are Carrying Different Currents and Turn it OFF , Either Way you are Protected ,
 
;) ( if you get Stuck , Remember Always Look Up , 17th Ed , p/29 Definitions RCDs , RCBOs , RCCBs : Appendix 3 , Table 3A p/243 RCDs )

RCDs :
Rewireable Fuses , Cartridge Fuses and MCBs Only Offer Protection for the Installation and Appliances and Not Personal Protection ( Additional Protection 30mA )

TT , Systems
100mA Trips are Commonly Installed in Houses where an Earth was Not Provided by the Local Electrical Company such as in Remote Countryside Areas so an Earth Electrode in the Form of a Earth Rod was Driven into the Ground and is Used as the Earth Path , The 100mA RCD does Afford Better Protection for the Installation than Fuses or MCBs Alone but Not Personal Protection , ( Additional Protection 30mA )

What’s the Difference between an RCD and an RCBO ???
30mA RCDs Afford Only Personal Protection , and Not Circuit Overcurrent Protection which would be Provided by Individual MCBs or Fuses , A 30mA RCBO is Combined RCD & MCB Unit which Protects Individual Circuits from Overload and Also Affords Personal Protection ,

17th Ed : RCBO , A Residual Current Operated Switching Device Deigned to Perform the Functions of Protection Against Overload and / Or Short-Circuit ,
17th Ed : RCD , Residual Current which Cause the RCD to Operate Under Specified Conditions ,

● When Testing the Operation of a Residual Current Device it is Imperative that the Potential of the Circuit Protective Conductor Does Not Rise Above Earth Potential by More Than 50V ,

Earth Potential ??? ( R ≤ 50 / 30mA , 50 ÷ 30 = 1667Ω ) 411.5.3 / table 41.5

Why Polarity ??
Polarity Test is Conducted to Verify , Every Fuse and Single Pole Control and Protective Device is Connected in the Line Conductor Only , 612.6 (i)

● The Amount of Current that Can Cause Death is Very Small , in Fact its just 50mA ( milliamps ) much Less than 3A Fuse ,
Many Believe that it is Voltage that Can Kill whereas in Actual Fact it is the Current that Causes a Shock and can Prove Fatal !!!!

Plug in RCD ??? Functional Testing ,
( 612.13.1 , Any Test Facility Incorporated in the Devices Shall be Verified )

It is Vitally Important to Regularly Check the Operation of All RCDs ,
● A Plug in Type RCD should be Checked each and Every Time by Plugging in and Operating the Test Button Prior to Use ,
● For Those Contained within Split-Load C/U , again Check Regularly by Operating the Test Button and Ensure that as Per IEE Regulations that the Whole Installation and RCD Operating Times are Tested Using the Correct Instruments ,

( When Testing RCDs ) 0° / 180° , Positive & Negative Half-Cycles and Record the ►Longer Operating Time ,
 
;) ● Frequency ,
In Alternating Current : ▼
The Rate at Which the Current Changes Direction – in the UK Typical 50 Hertz , One Complete Cycle in One Second is 1 Hertz ,
● Alternating Current ( AC )
The Type of Mains Electricity Used in the UK , having a Cyclical Current Waveform , Normally Used in UK Houses at 230V ( RMS ) Alternating at 50 Times per Second ( 50 hertz )
● Direct Current ( DC )
Unlike Alternating Current , the Flow of Electricity does Not Alternate / it Flows in just One Direction , Normally Used in Low Voltage Electronic Circuits and Computers etc. Around the House and is Usually Derived from the Alternating Main via a Power Supply

● Separated Extra Low Voltage ( SELV )
A Circuit Operating at Less than 50V a.c Or 120V ripple-Free d.c . Via a Step Down Transformer from the Mains ,
● Overcurrent ,
A Current Exceeding the Rated Value , the Circuit / Appliance should be Protected by a Circuit Breaker or Fuse so than Any Overcurrent in the Circuit is Short Lived , for Cables the Rated Value is their Current Carrying Capacity .
● Double Pole Switch
A Switch which Breaks ( or Makes ) Both the Line and Neutral Lines with One Throw of the Switch ,

CCU : Cooker Control Unit ,
This is Normally a Two-Pole Switch that is Located within 2 Meters of an Electric Cooker , sometimes these Switches also Incorporate a Socket Outlet ,
CU : Consumer Unit ,
CCT : - Circuit – Any Combination of Wiring and Components that Provides a Path for the Flow of Electricity ,
ELV : Extra Low Voltage / Voltage that is Below 50V a.c.
FCU : Fused Connection Unit ,
kW : Kilowatt , One Thousand Watts of Electricity ( ten 100 Watt light Bulbs Use One kilowatt of Electrical Power ,
MICC : Mineral Insulated Copper Cable , / Often Called Pyro ,
● VD : Voltage Drop in a Circuit Normally Occurs when Current is Passed through a Circuit , The Greater the Résistance of the Circuit the Greater the Volt Drop ,
 
:confused: Safety Working !!!!

Safety is of Utmost Importance When Working with Electricity , Develop Safe Work Habits and Stick to Them , Be Very Carful with Electricity , it may be Invisible , But it Can be Dangerous if Not Understood and Respected , Amber ;)
 
:eek: As My Mate , Michel Cane , Would Say “ a Lot of People Don’t Known That ,

Current ( Named after Andre Ampere 1775 – 1836 )

● Current is Electrical Flow ( Movement of Electrons ) Moving Through a Wire ,
● Current Flows in a Wire Pushed by Voltage ,
● Current is Measured in Amperes , or Amps , for Short ,
● An Ohmmeter Measures Current Flow in Amps , it is Inserted into the Path Or Current Flow , Or in Series , in a Circuit ,
- Electrons in Motion are Current Flow and the Ampere is the Unit of Measurement for this Current Flow ,
● The Symbol “ I “ is Used in Calculations’ and Schematic Drawings to Designate Current Flow ,
○ I = Current Flow ( Ampere )
○ To Determine if the Load is to Heavy for the Circuit , Divide Watts by Volts to Get Amperes ,
○ Thus , 2000W / 230V = 8.6 Amperes ( 8.6 Amperes is Under the 10 Amperes Fuse ) W ÷ V = I

Voltage ( Named after Alessandro Volta – 1745 / 1827 )

● Voltage is Electrical Pressure , a Potential Force or Difference in Electrical Charge between Two Points ,
● it can Push Electrical Current Through a Wire , but Not Through its Insulation ,
● Voltage is Measured in Volts , One Volt can Push a Certain Amount of Current , Two Volts Twice as Much , and So On ,
● A Voltmeter Measures’ the Difference in Electrical Pressure between Two Point in Volts ,
○ A Voltmeter is Used in Parallel ,
● Voltage is Usually Designated by the Letter ( E ) in the Ohms Formula ,
● it Refers to the Pressure which is Required to Force the Electrons Through the Circuit ,
● This is the Pressure that Makes them Move when an Appliance Stats or a Light is Turned On ,
● This Pressure is Available in Your Wiring Circuit all the Time , Whether you are Using your Electrical Equipment Or Not ,
● Voltage is Called “ Electromotive Force “ Whenever Two Points of Unequal Potential Or Voltage are Connected , Current Flows ,
● The Greater the “ EMF “ Or Voltage , The Greater the Amount of Current Flow ,
● Voltage will Differ On Certain Types Of Equipment , but it is Usually 230 Volts ,
○ Some Equipment that Operates On One Volt will Show a High and Low Voltage On the Nameplate , Such as ( 100 / 120 ) example Only !!
○ This Means that Any Voltage between These Two Figures should be Satisfactory for Operating that Piece of Equipment ,
○ Using a Higher Voltage will Result in a Greater Current Flow and BURN OUT the Lamp , While a Lower Voltage will Not Cause Enough Current to Make the Lamp Light Up Normally ,

PS , Can’t Shut Michel Cane Up , ;)

Watts : Named after James Watt ( 1736 – 1819 ) He Created the Term “ Horsepower , and Invented the ( Steam Engine ) :

● Electricity is Measured in Units of Power Called Watts ,
● One Watt is a Very Small Amount of Power , it Would Require Nearly ( 750 Watts ) to Equal One Horsepower : PS 1Hp – 750W ,
● A kilowatt Represent 1,000 Watts ,
● A kilowatt-hour ( kWh ) is Equal to the Energy of 1,000 Watts working for One Hour ,
● The Amount of Electricity a Power Plat Generates Or a Customer Uses Over a Period of Time is Measured in kilowatt Hours ( kWh )
● Kilowatt Hour are Determine buy Multiplying the Number of kW,s Required by the Number of Hours of Use , You buy Electrical Energy by kilowatt Hours ,
○ for Example ! if you Use a 40 Watt Light Bulb 5 Hour a Day , you have Used 200 Watts of Power , Or 0.2 kilowatt-hours of Electrical Energy , Or 100 Watt Light Bulb for 10 Hours / that is 1 kilowatt Hour ,
○ To get kilowatt hours of Electrical Energy , You Divide the Number of Watt – Hours by 1,000 , So 1,000/1,000 = 1 kWh ,
● Watts can be Measured with an Instrument Called a Watt Meter ,

Résistance ( Named After Georg Simon Ohms ( 1787 / 1854 )

● Résistance Opposes Current Flow , it is Like Electrical “ Friction “ This Résistance Slows the Flow of Current ,
● Every Electrical Component Or Circuit has Résistance ,
● This Résistance Charges Electrical Energy into Another Form of Energy / Heat , Light , Motion,
● Résistance is Measured in Ohms ,
● A Meter , Called an Ohmmeter , Can Measure the Résistance of a Device in Ohms when No Current is Flowing ,

Factors Affecting Résistance , ♫♫♫
Five Factors Determine the Résistance of Conductors ▼
Length of the Conductor , Diameter , Temperature , Physical Condition , and Conductor Material ,

Length ▼
Electrons in Motion are Constantly Colliding as Voltage Pushes them Through a Conductor , ↔ if Two Wires are the Same Material and Diameter , The Longer Wire will have More Résistance than the Shorter Wire , Wire Resistance is Often Listed in Ohms per Foot ( e.g. Spark Plug Cables at 5Ω per Foot ) Length Must be Considered when Replacing Wires ,

Diameter : ▼
Large Conductors’ Allow More Current Flow with Less Voltage , if Two Wires are the Same Material and Length , the Thinner Wire will have More Résistance than the Thicker Wire ,
( Size/Gauge : Thicker with Less Résistance and More Current Capacity )
( Thinner with More Résistance and Less Current Capacity )

● All Cables Must be The Proper Size for The Circuit Current , ♫♫♫
 
:cool: Temperature : ▼

In Most Conductor’s Résistance Increases as the Wire Temperature Increases , Electrons Move Faster , but Not Necessarily in the Right Direction , Most Isolators’ have Less Résistance at Higher Temperatures ,

Physical Condition : ▼

Partially Cut Or Nicked Wire will Act Like Small Wire with High Résistance in the Damaged Area , A Kink in the Wire , Poor Splices , and Loose Or Corroded Connections’ also Increase Résistance , Take Care Not to Damage Wires During Testing Or Stripping Insulation ,

Material :

Materials with Many Free Electrons are Good Conductor’s with Low Résistance to Current Flow , Good Conductor’s are Cooper , Aluminium and Gold ,
Materials with Many Bound Electrons are Poor Conductor’s ( Insulators ) with High Résistance to Current Flow , They are ; Rubber , Glass , Paper , Ceramics , Plastics , and Air – All have High Résistance ,

Ohms Law :
Georg Simon Ohm (1787 /1854 ) Was the Person Who Discovered how Amps , Résistance , Power and Watts are Tied Together Mathematically ,

Ohm’s Law Say’s , The Current in a Circuit is Directly Proportional to the Applied Voltage and Inversely Proportional to the Amount of Résistance . This Means that if the Voltage Goes Up , The Current Flow Will Goes Up , and Vice Versa , Also , as Résistance Goes Up , The Current Goes Down , and Vice Versa ,
● Based On This Law , Any Given Voltage , Résistance , Or Current can be Found by Knowing Any 2 of the 3 Factors ,
These Factors are Know As , ( E = Volts , I = Current , R = Résistance ,

Current is Affected by Either Voltage Or Résistance , if the Voltage is High or the Résistance is Low , Current will be High , if the Voltage is Low or the Résistance is High , Current will be Low ,

Résistance is Not Affected be Either Voltage Or Current , it is Either too Low , Okay , Or too High , if Résistance is too Low , Current will be High at Any Voltage , if Résistance is too High , Current will be Low if Voltage is Okay ,

Michel Cane Here , Did you Know That !!!!

The Purpose of a Generator is to Convert Motion into Electricity , The Generator is a Simple Device that Moves a Magnet Near a Wire to Create a Steady Flow of Electrons , it Uses a Magnet to Get Electrons Moving , if you Move a Magnet Near a Wire ,The Magnetic Field will Cause Electrons in the Wire to Move , Because the Electrons Flow in One Direction and in the Other , The Generator Produces Alternating Current ,

:eek: PS , Mac are you Still Out There ??? Amber ,

;) Q ) is This Helping Anybody Out There , Amber , Sorry Must Dash Going for A Pint With Michel Cane , I’ll Be Back Before Xmas ,
 
:confused: Electron Theory ;

Electron Theory Helps to Explain Electricity , The Basic Building Block for Matter , Anything That Has Mass and Occupies Space , is An Atom ,
All Matters , solid , Liquid , Or Gas , - is Made Up of Molecules , Or Atoms Joined together , These Atoms are the Smallest Particles into Which an Element Or Substance can be Divided without Losing its Properties , There are Only about 100 Different Atoms that Make Up Everything in the World the Features that Make One Atom Different from Anther also Determine its Electrical Properties ,

Inside An Atom
Electron / Nucleus
Atom Structure , An Atom is Like a Tiny Solar System ,
The Centre is Called the Nucleus , Made Up of Tiny Particles Called Protons and Neutrons , The Nucleus is Surrounded by Clouds of Other Tiny Particles Called Electrons , The Electrons Rotate the Nucleus in Fixed Paths Called Shell or Rings , Hydrogen has the Simplest Atom with One Proton in the Nucleus and One Electron Rotating Around it , Copper is More Complex with 29 Electrons in Four Different Rings Rotating Around a Nucleus that has 29 Proton and 29 Neutrons , Other Elements have Different Atomic Structures ,

Atoms and Electrical Charges ,
● Each Atomic Particle has an Electrical Charge ,
● Electrons have a Negative ( - ) Charge ,
● Protons have a Positive Charge ( + )
● Neutrons have No Charge ; They are Neutral ,

In a Balanced Atom , the Number of Electrons Equals the Number of Protons , The Balance of the Opposing Negative and Positive Charges Holds the Atom Together , Like Charges Repel , Unlike Charges Attract , The Positive Protons Hold the Electrons in Orbit , Centrifugal Force Prevents the Electrons from Moving Inwards , and , the Neutrons Cancel the Repelling Force between Protons to Hold the Atom’s Core Together ,

Positive and Negative ions ,
If an Atom Gains Electrons , it becomes a Negative ion , if an Atom Loses Electrons , it becomes a Positive ion , Positive ions Attract Electrons from Neighbouring Atoms to become Balanced , This Causes Electron Flow ,

Electron Flow :
The Number of Electrons in the Outer Orbit Determines the Atom’s Ability to Conduct Electricity , Electrons in the Inner Ring are Closer to the Core , Strongly Attracted to the Protons , and are Called Bound Electrons , Electrons in the Other Ring are Further Away from the Core , Less Strongly Attracted to the Protons , and are Called Free Electrons ,

Electrons can be Freed by Forces such as Friction , Heat , Light , Pressure , Chemical Action , or Magnetic Action , These Freed Electrons Move Away from the Electromotive Force , Or EMF ( “ Electron Moving Force ” ) from One Atom to the Next ► ( A Stream of Free Electrons Forms An Electrical Current )

Conductors and Insulators :
The Electrical Properties of Various Materials are Determined by the Number of Electrons in the Outer Ring of their Atoms ,
Conductors - Materials with 1 to 3 Electrons in the Atom’s Outer Ring make Good Conductor’s , Gold , Silver , Cooper , Aluminium , Iron , etc , All have Free Electrons , the Loose Electrons make it Easy for Electricity to Flow Through these Materials , so they are Known as Electrical Conductor’s , The Moving Electrons Transmit Electrical Energy from One Point to Another , The Electrons are Held Loosely , there’s Room for More , and a Low EMF will Cause a Flow of Free Electrons ,

Insulator’s :
Materials with 5 to 8 Electrons in the Atom’s Outer Ring are Insulators , The Electrons are Held Tightly , the Ring’s Fairly Full , and a Very high EMF is Needed to Cause Any Electron Flow at All , Such Materials Include Glass , Rubber , and Certain Plastics ,
These are All Examples of Materials in which Electrons Stick with their Atoms , Because the Electrons Don’t Move , These Materials Cannot Conduct Electricity Very Well , if at All ,

Current Flow ;
The Electron Theory States that Current Flows from ( - ) to ( + ) … Excess Electrons Cause an Area of Negative Potential ( - ) and Flow Towards an Area Lacking Electrons , an Area of Positive Potential ( + ) , To Balance the Charges ,
 
:confused: Circuit Protection ,
When a Fuse Blows or a Circuit Breaker is Tripped ,
Never Replace a Fuse with One that is Larger than that Specified for the Circuit , Why ? A Fuse that is too Large will Not Protect Against An Overload , Which Can Cause a Fire ,

Never Push Yourself when Working On any Electrical Project , Make Sure you give Yourself the Time to Think the Project Through Thoroughly , Mistakes Happen when We Rush Jobs , Use Good Judgment ,

Several Factors Determine the Effect a Shock will Have On a Human Body ,
(1) The Duration of Contact ,
(2) The Amperage ,
(3) The Path the Current Takes Through the Body , and
(4) The Electrical Résistance of the Body ,

Taken Together , These Factors can Produce some Surprising Results ,
Example , The Current from a 7 ½ Watt Christmas Tree Bulb ( 60/1000 of an Ampere ) can Give a Severe Shock

Always , Verify that the Circuit is DEAD before Working On it : LOCK it OFF MCBs , Why ? To Ensure Nobody Attempts to Restore Power While you are Working on the Circuit , ( Be Safe at All Times )
 
;) Power ratings
Resistors often have to carry comparatively large values of current, so they must be capable of doing this without overheating and causing damage. As the current has to be related to the voltage, it is the power rating of the resistor that needs to be identified.

The power rating of a resistor is thus really a convenient way of stating the maximum temperature at which the resistor is designed to operate without damage to itself. In general, the more power a resistor is designed to be capable of dissipating, the larger physically the resistor is. The resulting larger surface area aids heat dissipation.

Resistors with high power ratings may even be jacketed in a metal casing provided with cooling ribs and designed to be bolted fl at to a metal surface – all to improve the radiation and conduction of heat away from the resistance element.

Power is calculated by:
P = V × I

Instead of V we can substitute I × R for V and V/R for I. We can then use the following equations to calculate power:
P = I2 × R or P = V2 / R
What would the power rating of the 50Ωresistor be ?

P = V =I = 4 =0.08 = 0.32 watts
P = I2 =R = 0.08*2 =50 = 0.32 watts
P = V2 / R = 4 x 4 / 50 = 0.32 watts

( 4V : P = V =I ( P = I2 =R ( P = V2 / R , I = 80mA → 50Ω
Normally only one calculation is required. Typical power ratings for resistors are

Carbon resistors 0 to 0.5 watts
Ceramic resistors 0 to 6 watts
Wire wound resistors 0 to 25 watts

Manufacturers also always quote a maximum voltage rating for their resistors on their data sheets. The maximum voltage rating is basically a statement about the electrical insulation properties of those parts of the resistor that are supposed to be insulators (e.g. the ceramic or glass rod which supports the resistance element or the surface coating over the resistance element).

If the maximum voltage rating is exceeded there is a danger that a flashover may occur from one end of the resistor to the other. This flashover usually has disastrous results. If it occurs down the outside of the resistor it can destroy not only the protective coating but, on film resistors, the resistor film as well

If it occurs down the inside of the resistor the ceramic or glass rod is frequently cracked (if not shattered) and, of course, this mechanical damage to the support for the resistance element results in the element itself being damaged as well.

R1 is the Résistance of Line Conductor ,
R2 the Résistance of Line Protective Conductor ,

Continuity
Circuit protective conductors ( CPCs ) including main and supplementary protective bonding conductors

Regulations state that every protective conductor, including each bonding conductor, should be tested to verify that it is electronically sound and correctly connected. The test described below will check the continuity of the protective conductor and measure R1 + R2 which, when corrected for temperature, will enable the designer to verify the calculated earth fault loop impedance (Zs). For this test you need a low reading ohmmeter.

Test method 1. Before carrying out this test the leads should be ‘ Nulled out’. If the test measurement does not have this facility, the resistance of the leads should be measured and deducted from the readings. The line conductor and the protective conductor are linked together at the consumer unit or distribution board. The ohmmeter is used to test between the line and earth terminals at each outlet in the circuit. The measurement at the circuit’s extremity should be recorded and is the value of ( R1 + R2 ) for the circuit under test. On a lighting circuit the value of ( R1 ) should include the switch wire at the luminaires. This method should be carried out before any supplementary bonds are made.

Test method 2. One lead of the continuity tester is connected to the consumer’s main earth terminals The other lead is connected to a trailing lead, which is used to make contact with protective conductors at light fittings, switches, spur outlets etc. The resistance of the test leads will be included in the result; therefore the resistance of the test leads must be measured and subtracted from the reading obtained (since the instrument does not have a Nulling facility). In this method the protective conductor only is tested and this reading (R2) is recorded on the installation schedule.

( Most New Tester’s have Nulling Facility Now )
 
;) Is Low Voltage Lighting the Same as Low Energy ?
No! It’s the watts that count, not the volts.

There is a common misconception that low voltage lighting systems are the same thing in terms of energy efficiency as low energy lighting systems.

Measuring energy

Energy is measured in watts – your electricity bill probably shows how many kilowatts you have used. A kilowatt is 1000 watts.

Therefore, if you can produce a lot of light while using a small amount of watts you have a low energy light, and a cheaper electricity bill.

You probably know that low energy light bulbs have a small wattage rating and are often compared to an equivalent wattage. You might see that an 11w low energy bulb is the equivalent of a 60w normal bulb. This is only comparing the amount of light that is produced, it has nothing to do with the amount of energy consumed.

Volts, amps and watts

To show that a low voltage light is not a low energy light, we will compare these three lights:

· 50w low voltage spot light
· 50w mains voltage spot light
· 9w low energy spot light.

All three examples will produce about the same amount of light, but only one will cost less to run.

watts = volts x amps. Once we know this we can easily show that the maths confirms the number of watts used by each of the three example light:

50w low voltage spot light , Volts :- The electric supply connected to the light) 12V :- Amps (watts divided by volts) 4.17A ( Watts (as described by the product)

50w mains voltage spot light , Volts :- The electric supply connected to the light) 230V :- Amps (watts divided by volts) 0.21A :- Watts(as described by the product) 50W

9w low energy spot light , Volts :- The electric supply connected to the light) 230V :- Amps (watts divided by volts) 0.03A :- Watts(as described by the product) 9W

As you can see – the 230v 50w bulb uses exactly the same amount of watts (power) as the 12v 50w bulb.

But doesn’t it use less power because it’s running at 12 volts?

No – watts are watts. It doesn’t matter what the voltage is. We can show this more clearly by explaining about transformers:
Transformers

Low energy lighting such as the 9w bulb in our example will generally run at the full mains voltage, without requiring any change in the voltage.

Most low voltage lighting runs at 12 volts so unless you’re running it from a battery (e.g. in your car) there has to be a transformer to reduce the mains electricity supply from 230 volts to 12 volts. Some light fittings have a transformer built into them, and sometimes a separate transformer is required.

Transforming volts and amps

When a transformer transforms a voltage it also transforms the available amount of amps – In the table above you can see that the 12v light uses a lot more amps then the mains voltage lights.

The available amps are transformed by the same ratio as volts but in the opposite direction, so if the voltage is reduced by 20 times (230v to 12v) the amps are increased by 20 times (0.21 to 4.2).

In our above example the voltage has been reduced by 20 times, so the amps have increased by 20 times, but the wattage is the same.

Additionally because the transformer efficiency will not be 100% (some energy is lost in the transformation) the 12v bulb might even more use more power than the 230v one, as the transformer will be ‘using’ some as well as the light.

Is low voltage the same as low energy?

No – it’s the watts that count, not the volts.

Make sure you have a low wattage lighting system to make sure you’re saving your wallet and the environment by using low energy lighting.
 
;) Parallel Direct Current Circuit ,

Summary of Parallel Circuit ,
Total Voltage = E(1) = E(2) = E(3) … etc, Total Résistance = Volt’s … Amperes’
To Determine the Total Résistance in a Parallel Circuit when the Total Current and Total Voltage are Unknown Use Either of the Following Formulas ,
( Rt = 1 … 1/R1 + 1/R2 + 1/R3 + …. Etc ,

For Two Resistor’s in Parallel , Use This Formula , Called / “ Product Over the Sum “
( Rt = R(1) * R(2) …. R(1) + R(2)

Power in Single Phase Resistive Circuit’s , ( Where Power Factor is 100 Percent )
( These Formulas are Commonly Used to Solve most Circuit Power Problems on Test’s )

● To Determine the Power Consumed by an Individual Resistor in a Series Circuit Use this Formula: ( Power = I2 x R )
● To Determine the Power Consumed by an Individual Resistor in a Parallel Circuit Use this Formula: ( Power = E2 – R
● To Determine the Total Power Consumed by an Individual Resistor in a Parallel Circuit Use this Formula: ( Power = E ( Total Voltage ) x I ( Total Current )

● The Total Résistance of Resistor’s in Parallel is always Less than the Value of any One Resistor ,
● The Total Résistance of Parallel Resistor’s that are all the same Value is that Value Divided by the Number of Resistor’s
● Always Use the Product Over Sum Rule to Break Down Two Parallel Resistor’s into One Resistor’s , This is much Easier than trying to Solve Large Algebraic Expression’s

● 746 Watts is Equal to One Horsepower .
● Efficiency is Equal to Output Divided by Input ,
● in Inductive Circuit’s Current Lag’s Voltage ,
● in Capacitive Circuit’s Current Leads Voltage ,
● Power Factor is a Measure of how Far Current Leads or Lag’s Voltage ,

Power in Alternating Current Circuit’s where Power Factor is Not 100 %
Power = E x I x Power Factor , ( for Single Phase )
Power = E x I x 1.732 x Power Factor ( for Tree-Phase )

This Power is Also Called True Power or Real Power as Opposed to Apparent Power Found be Calculating Voltage – Amperes’
Voltage – Amperes’ = E x I ( for Single Phase )
Voltage – Amperes’ = E x I x 1.732 ( for Tree-Phase )

It can Readily be Determined by Algebra that
Power Factor = True Power …. Apparent Power ,

Motor Application Formulas ,
Horsepower = 1.732 x Volt’s x Ampere’s x Efficiency x power factor
( for Three-Phase Motor’s ) 746

Three-Phase Amperes’ = 746 x Horsepower … ( for Three-Phase Motor’s ) 1.732 x Volts x Efficiency x Power Factor ,
Synchronous RPM = Hertz x ?? …. Number of Pole’s ?? etc.

Q) Amber asking do We Still Use the Term ( Leads or Lags ) PS must Know , Thank You , :confused:
 
;) APPLICATIONS RADIAL CIRCUITS
Measurement of impedance of a ‘live’ electrical circuit cannot be made using a continuity tester. Thus an earth loop tester must be used.

Earth loop testers measure circuit loop IMPEDANCE.◄

110 V INSTALLATIONS
110 V a.c systems including 110 V Centre tap to earth (55 V phase to earth) can be tested on the secondary winding, either at 110 V or 55 V on the centre tap to earth.
 
;) Resistance and the Conductor

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

This relates directly to our cabling in that if a cable is too small (i.e. c.s.a. of 1 mm2) to carry the current of the circuit we simply choose a larger c.s.a. cable (say 1.5 mm2) so that the current is carried through the cable which has a lower resistance.

So it is worth realising that cables that possess resistance will directly affect the efficient working of our circuits. The other factors that affect the resistance of our cable are:

1. Heat (e.g. in the case of Ambient temperature).
2. The actual material the cable is made from.
 
;) Basic’s :

You Cannot Covert Watts to Amps . since Watts are Power ( Ultimately Horsepower ) and Amps are Current ( or Flow if you Like ) Unless you have the Added Element of Voltage to Complete the Equation . You must have at Least Two of the Following Three :- Amps . Volts . & Watts . to be Able to Calculate the Missing One . Since Watts are Amps Multiplied by Volts . There is a Clear Relationship Between them ..
 
How to Remember . V◄ x ►A : kV◄ x ►A It’s the Same

( Computing Volt – Amps ( VA ) = Volts x Amps = 300VA )

( Computing Kilovolt – Amps ( kVA ) = Volts x Amps ÷ 1000 . • ( kVA Stands for “ Thousand Volt – Amps )
230V x 2.5A = 300VA ( 300VA ÷ 1000 = 0.3kVA ) .3kVA
 
All 3 Lights are 150 Watts . How much Current flows in the Neutral Wire .
a) 0 Amps . *
b) 1.2 amp .
c) 2.4 amps .

What does an “ Infinity “ Reading on an Ohm Meter Indicate .
a) Open Circuit . *
b) Short Circuit .
c) DC Circuit .
* Zero Indicates a Closed Circuit
* While Infinity Indicates an Open Circuit .

A Material with better Conductivity than Copper is .
a) Aluminium .
b) Silver . *
c) Steel .

a Parallel Path of Low Résistance is Commonly Referred to as .
a) Resonance Circuit .
b) Short Circuit .*
c) Open Circuit .

in a Transformer . the Oil is Primarily Used for .
a) Insulating .
b) Lubrication .
c) Cooling . *

If the Voltage to a Circuit Increases . the Current .
a) Increases . *
b) Stays the Same .
c) Decreases .

Most Electricity is Produced by .
a) Magnetism . *
b) Chemical Reaction .
c) Pressure .

In Flemings Left Hand rule . what Direction does the First Finger Point .
a) North .
b) The Direction of the Magnetic Flux . *
c) South .

A Transformer Changes a.c. to d.c.
a) True .
b) False . *

what kVA rating is Required for a Transformer that must Handle a Maximum Load Current of 8A with a Secondary Voltage of 2 kV.
a) 4 kVA
b) 8 kVA .
c) 16 kVA . * x

An Arrow drawn through the Schematic Symbol of an Inductor Indicates that the Inductor is .
a) d.c.
b) a.c.
c) Adjustable . *

Inductance is the Property of an Inductor that Produces an Opposition to any Change in Current .
a) True . *
b) False .

A Voltmeter Generally Reads .
a) Peak to Peak Voltage .
b) Average Voltage .
c) RMS Voltage . *
 
There are Two Groups of Test :

Dead & Live .
Dead :- Test Prior to the Installation being Energized . ( Before )
Live :- Test Following Installation being Energized . ( After )

Live Testing : is to Ensure that Once Energized . The Protective Device are Suitable for the Fault Currents Likely to Occur & will Operate Correctly in the Time Specified by the Regulation’s in the Event of a Fault

Dead Testing : is to Ensure that the Cabling has not been Damaged . & The Electrician has Not made any Mistakes .& that the Circuit(s) are Safe to Energise .
 
● Reference to maintained and non-maintained systems are made to ? ( Emergency lighting installations )
● The industry body that represents and negotiates on behalf of employees in the electrical contracting industry is the ? ( JIB )
● A large industrial panel feeding a large factory has several components installed to monitor voltage current and power consumption . this is known as ? ( Instrumentation )
● A component installed to detect increase in temperature is known as a ? ( Heat Detector )
● A measurement of 600mm taken off a site drawing that has a scale of 1:100 equates to ? ( 60 meters on site )
● A measurement of 20mm taken off a site drawing that has a scale of 1:20 equates to ? ( 0.4 meters on site .)
● BS-7671 is Classed as a ? ( Non statutory document )
● Which of the following is necessary for an electrician to install equipment on a construction site ? ( Drawings & Diagrams )
● When work is expected to be performed on an existing live circuit we should ? ( Safety isolate the circuit first )
● Fibre optic cabling is used in the transmission of ? ( Data )
● A tender to apply to undertake work is normally completed by the ? ( Estimator )
● The responsibility for health & safety when working in a domestic situation is ? ( The person carrying out the work )
● When considering the completion of work under live conditions . what must we do first ? ( Perform a Risk Assessment )
● What system can control heating & ventilation within a construction via a series of sensors ? ( Building management system )
● A foreman ? ( Runs the day to day operations on a construction site )
● Working in areas that have a higher than normal dust content should necessitate the need for ? ( A respirator )
● One method of ensuring that site drawings are easy to interpret is by using ? ( BS-EN 60617 symbols )
● The main purpose of a circuit diagram is to show how the installation ? ( Functions )
● The amount of electrical current that has the potential to kill is approximately ? ( 0.05A )
● Installation of a complicated piece of machinery should be completed using the working drawings and ? ( Manufacturers instructions )
● the IEE Wiring Regulations’ give advice on electrical installation but is fundamentally based on ? ( The Electricity at Work Regulations )
● The simplest method of displaying for a large installation is by a ? ( Block diagram )
 
After Midnight 2.02 minutes past

• A force of 20kN moves an Object a distance of 5m . the work done is ( 100kJ ) * Work Done = Force x Distance .
• MIMS cable comes with the Option of being sheathed or unsheathed . where might you use sheathed cable : ( In areas of high moisture content )
* Reduces the chances of the insulation getting damaged .
• A miniature circuit breaker conforms to what British Standard : ( BS-EN 60898 )
* European Standard .
• Which of the following from the list is the best conductor of electricity : ( Platinum )
* The most expensive too .
• An ammeter used to record current is connected in : ( Series )
* Current stays the same in Series .
• A standard circuit draws 5A and feeds a load with a résistance of 0.5Ω . what will be the total power : ( 12.5W )
* P = I Squared x R .
• Excess current flowing in a circuit that is electrically sound is known as : ( Overload Fault )
* Not a Short or Earth Fault .
• The r/ms value of a sine wave is calculated using the peak value multiplied by : ( 0.707 )
* 0.707 .
• Before being used . a ladder must be inspected by : ( Intended User ) YOU
* hopefully you before you get up there .
• An 110V transformer designed to be used on a construction site is Centre Tapped for additional protection to : ( 55V to Earth )
* Reduce voltage to Earth .
• The cables connecting together Extraneous Conductive Parts to the main Earthing Terminal are called : ( Equipotential bonding conductors )
* To maintain an equal potential .
• if Non-sheathed cables are specified on an installation they should be : ( Installed in conduit or trunking )
* Have some Mechanical protection .
• if a copper busbar is drawing a current of 300A . what will be the Physical effect on the actual busbar : ( it will expand )
* Less heat more Résistance .
• Percentage efficiency can be calculated by : (
* Output/input times 100 .
• if 3 conductors equal in length and in length and with a resistance of 1.5Ω are connected in parallel . what is the total résistance : ( 0.5Ω )
* Use the reciprocal calculation . 1/Rt = 1/R1 etc .
 
• if the peak voltage is given as 200V . what would be the average voltage : ( 127.4V )
* remember 0.637 for the average value .
• Three resisters of value 1.0Ω . 1.2Ω & 1.8Ω are connected in series across a 24V supply . what is the total current drawn in the circuit : ( 6A )
* Ohms law & adding résistance in series .
• The SI : unit electrical pressure is the ( Volt )
* Difference in potential . also called the emf
• Losses occurred in a transformers can be the results of ( Eddy currents )
* Lost magnetic current .
• the ►►maximum operating temperature of XLPE insulated cable is ( 90°O ) Watch the Wording / Two XLPE Q) . 90°O / 70°O
* increased over PVC insulation .
• transformers usually have their windings laminated . this is done to reduce ( Eddy currents )
* The name of the current .
• The primary winding of a transformer is connected to the ( Supply )
* Primary = first side .
• A galvanometer can measure electrical current using ( Magnetic fields )
* Older style clamp on ammeters use the principle .
• Isolating transformers operate on the principle ( Mutual induction )
* Means 2 separate coils .
• if the magnetic flux in a coil is divided by the cross sectional area of the coil . the unit produced is measured in ( Teslas )
* Magnetic flux density .
• The application of the electromagnet can be clearly demonstrated in the construction of ( Relays )
* Thick of the effect of winding around a ferrous core .
• Standard voltages in the UK used for distribution to consumers are commonly ( 11kV : 400V : 230V )
* Think about domestic and industrial .
 
• One example of an exposed conductive part is . ( A metalclad one way switch ) it could be a 3-way / 2-way ( Metal ) Hands !!!!!
* Exposed = part of a electrical system .
• A metal gas pipe entering a building is classed as an ( Extraneous conductive part ) ◄
* Not part of a electrical system but can introduce a potential ..
• The external loop impedance of an installation is abbreviated to ( Ze )
* Earth fault loop impedance .
• Protection from fault contact can be achieved using ( ADS )
* When it happens . what should happen to the circuit .
• One example of an exposed conductive part is ( The outer casing on a single Phase Motor )
* Exposed = part of a electrical system .
• Excess current flowing in a Circuit that is electrically sound is known as ( An overload fault ) ◄◄
* Not a short circuit or earth fault then …
• One reason for using circuit breakers rather than other cartridge type fuses is ( Can be easily reset after a fault ) ◄
* How many do you need .
• An earthing system that uses a separate conductor as a return path for fault current is called ( TN-S )
IT ) TN-C-S ) TN-C ) TN-S ** )
• A single pole switch that forms part of a lighting circuit switches the ( Phase or Line Conductor )
* Single Pole . which is the important conductor .
• if a circuit supplies portable equipment outside the equipotential zone . it must also be protected by a ( RCD ) 17th Ed
* Supplementary or additional protection .
• TN-C-S systems use a PEN conductor . what does PEN stand for ( Protective earthed neutral )
* Combined Neutral & Earth
• Protection from electrical shock by direct or basic contact is afforded by ( Barriers & enclosures )
* Prevent them touching live parts .
• A high breaking cartridge fuse conforms to what British Standard ( BS-88 part 2 )
* BS-88 -
• if non-sheathed cables are specified on an installation they should be ( Installed in conduit or trunking )
* Have some mechanical protection .
 
3.03 / 3 hour & minutes ( Junior Mebers . ( PLEASE DO NOT send DOWNLOAD ) :confused::confused: Amber

• a ) E = 2pΦN … 60 . ( Yes )
* Known as the emf generation formula . ( Yes )
• b ) E = ΦN … 60 x 2p .
• c) E = 2pΦN x 60 .
• d) E = N / 2p x 60 x Φ .
•• if a current of 200mA flows into a capacitor for 40mS . how much change will develop in the capacitor ( 8 mC )
* Quit .
• Made from a variety of materials . such as carbon . what inhibits the flow of current ( Resistor )
* Another work for inhibit .
• A kitchen installation contains a ring circuit with several appliances installed on it such as a dishwasher and a fridge . The RCD frequently trips . what might be possible cause . ( Nuisance tripping from earth leakage ) ◄◄
* it’s a pain in the backside .
• What is the best method of protection by a line Phase to earth fault ( RCD )
* What detects imbalances .
• Excess current that flows in a circuit which is electrical sound is known as ( Overload ) 17th Ed . p/27
* More and more and more .
• An office with a raised floor with an expectation that desks can be moved can be best supplied by a system of ( Busbar trunking ) * Plug in . plug out .
• A 30 kW 3-Phase delta connected motor has a power factor of 0.86 lagging . calculate the Line current ( 50.35A )
* Remember to take power factor into consideration .
• The best cable for supplying a remote part of an installation separated from the main building is ( XLPE/SWA )
* The strongest .
• Calculate the induced emf in a conductor with a length of 0.65m moving at right angles at a velocity of 2m/s through a magnetic field that has a flux density of 0.9 tesla . ( 1.17V )
* Hey Bill ?? .
• One method of improving the starting torque of a 3-Phase induction motor is to use ( Star/Delta starting )
* High torques start . low current run .
• A RCBO provides protection against ( Overload &/or Sort Circuit ) ◄ p/29 17th Ed . [ Earth fault current ]
* Best of both worlds ,
• How many numbers of turns are needed on a transformer if the primary windings are 1000 & the primary & secondary current are 5A & 20A respectively ( 250 turns )
* Follow the formula . Np/Ns equals VP/VS etc ….
• A cooper conductor has a resistivity of 1.78 x 10-8 Ω . Determine the résistance of 100m of 2.5mm2 ( 0.712Ω )
( Remember that . 10- Small 8 ) Resistivity times length divided by area .
• An earthing system that uses a separate conductor as a return path for any fault current is called ( TN-S )
* Separate . as in . both separate all the Time .
• Which supply system uses the neutral conductor also as an earth ( TN-C-S )
* What does PEN stand for ? .
• a circuit consisting of an inductance of 0.12H is connected to a 50Hz supply . the inductive reactance is ( 37.7Ω )
* Two times ( pi ) times frequency .
• The rotor conductors of a 3-Phase cage rotor inductance motor are constructed of solid conductors ( Shorted et each end of rings )
* Hint !! We need a current through them to create a magnetic field .
• Capacitors can be connected across the supply terminals’ of an electrical circuit to ( Reduce the supply current )
* Reduced power reduces the ……
• An eight pole motor operating on a 50Hz supply would have a Synchronous speed of ( 750 rpm ) you will get Cals . in working Sparkie ????
* Frequency divided by Pairs of poles .
• A purely capacitive circuit contains 2 capacitors in parallel of sizes 10µF & 36µF . has a supply frequency of 50Hz and a total current of 12A . what is the total power dissipated in a circuit ( 0W ) ◄
* Purely capacitive …. Think about it .
• Cables that provides a reduction in emission of toxic gases and has a higher operating temperature than PVC are known as ( LSF cables )
* Low smoke & fume .
• Speed control of a 3-Phase wound rotor induction motor can be achieved by ( Adjusting resistance across the slip rings )
* It’s dictated by current . what affects current .
• In order to improve the power factor of an inductive system ( A capacitor is connected across the supply )
* The opposite of inductance .
• The peak inverse voltage of a 10V diode is ( 20V )
* Twin peaks .
• The light loss factor is used in the calculation for illuminance . what is it for ( The total light depreciation at a given time compared to when brand new )
* Things get old . like us . they don’t work so good .
• A series a.c. circuit has a resistance of 3Ω and an inductor of 0.0127H connected across a supply frequency of 50Hz . what is the total circuit impedance ( 0.5Ω )
* Reactance & pythagorus will lead the way
 
• A standard iron cored transformer works on the principle of ( Mutual induction ) ( PLEASE DO NOT send DOWNLOAD )
* Affects another coil .
• Speed control of a 3-Phase induction motor can be achieved by ( Changing the voltage applied to the stator )
* What can be increase to increase or Decrease the current .
• A 90 mF capacitor is connected to a 100 Volt d.c. supply . calculate the charge stored in the capacitor ( 9 coulombs )
* Capacitance time voltage .
• A conductor 300m long is placed in and at right angles to a magnetic field with a magnetic flux density of 0.3 tesla . what is the force on the conductor if a current of 36A is passed through it ( 3.24 N )
* Hey Bill .
• A transistor can be used as ( A Switch )
* sometimes on . sometimes off .
• When starting a 400V 3-Phase cage rotor motor using a star/delta starter . the voltage across each stator Phase is ( 230 V start 400 V run ) ◄◄
* Less voltage . more current .
• The most common method of speed control on an induction motor is ( Frequency control )
* How do we calculate synchronous speed .
• A 4 pole 50Hz three phase induction motor has a 4% slip . the rotor speed will be ( 24 rev/sec )
* Work synchronous speed first then work back .
• The current produced in the rotor bars of a cage rotor motor is caused by ( Mutual induction )
* The stator affects the rotor .
• An RCD used as additional or supplementary protection on a circuit should be rated at ( 30mA )
* Touch voltage to be taken into account .
• A small heating circuit draws . 1.5kW of power and has an internal resistance of 0.38Ω . what is the total voltage drawn ( 24V )
* What are the formulas for calculating power .
• Which of the following is an acceptable method of obtaining an earth connection for a TT system ( Structural steel embedded in the ground )
* Which is the only one that cannot change .
• A circuit contains 3 capacitors in series of size . 19µF . 24µF & 32µF . what is the total capacitance in the circuit .( 8 µF )
* Capacitors add the opposite to reistors .
• Motors over the size of 0.37kW ◄◄ must have a means of ( Overload protection )
* Stop the motor running out .
• The type of motor stator which can be used on all cage motor ratings from fractional kW up to 1000 kW would be ( Soft Start )
* Not a hard start .
• A coil has self-inductance 1.5H , and the current through it changes from 0.8A to 0.4A in 0.02Sec calculate the emf . induced ( 30V )
* Change . over time . time inductance .
• A resistor and an inductor in a series circuit have a résistance of 6Ω and an inductive reactance of 8Ω respectively . what is the total impedance ( 10Ω )
* Follow Pythagorus .
• A supply system which uses the metal sheath of the cable to provide an earth connection is known as ( TN-S )
* Both separate .
• A silver band on a resistor indicates a tolerance of ( 10% ) Ps I got this when I was an Apprentice . this kind off Stuff !! : 90s
* Not as common . but still 10 star .
• A transistor can be used as ( An amplifier )
* Listen to that stereo .
• A capacitor start and run single Phase induction motor as a ( Two Phase motor ) Watch the Wording . ← ← ← ←
* Moves it out of Phase .
• In a star connected system . determine the line voltage if the Phase voltage is 660V ( 1143V )
* In star . IL = Ip .
• A four pole 50Hz three Phase induction motor is connected to a 400V supply . if the motor has 4% slip the rotor speed will be ( 1440 rpm )
* Work synchronous speed first work back from there .
• An increase in starting torque of a three Phase wound rotor induction motor can be achieved by ( Placing less résistance across the slip rings )
* More current can be achieved by .
• Protection of electrical cables in the event of a fire can be achieved by ( Installing FP200 cables )
* Fire proof .
• When a small voltage is applied to the base of a transistor . current flows between the ( Collector and the emitter )
* Collects and emits .
• When a single Phase capacitor start capacitor . run motor reaches its synchronous speed the centrifugal switch will ( Disconnect the start winding )
* What’s not needed when running .
• A streetlight contains a 2000cd light source 4m above the ground . What is the luminance directly below the lamp ( 125 lux )
* I/d -2 ( small 2 )
• A capacitor of capacitive Reactance 5Ω . an inductor of 8Ω inductive Reactance and a Resistor of 4Ω are connected in series to a 230V 50Hz supply . the total impedance of the circuit will be ( 5Ω )
* Pythagorus with a twist .
• A device consisting of 2 conductive plates separated from each other by a dielectric is known as a ( Capacitor )
* Two plates . think of the symbol .
• The star rotor windings of a 3-Phase wound rotor induction motor are connected in series to a bank of external resistors ( Slip rings & brushes )
* Think a.c. and how you connect power to a moving machine .
• A medium sized factory has a three-Phase load of 50 kVA & 30 kVAr Calculate the total kW ( 40 kW )
* Think & thank Pythagorus .

• In a capacitor start motor . the start and run windings are ( 90° out of Phase )
* Not quite 3 Phase degrees out .
• A short circuit is a ( Fault of negligible impedance between Line & neutral conductors )
* Virtually no résistance between them .
• A capacitor of 95µF is connected in parallel with a 20Ω pure resistor . the group is connected to a 230V . 50Hz supply . calculate the power dissipated in the circuit ( 2.64 kW )
* PURE resistor part should give it away .
• Simple D.C. rectification can be achieved by placing what into an A.C. circuit ( Diode )
* Lets through in one direction only )
• A conductor 500mm long is paced in and at right angles to a magnetic field with a magnetic flux density of 0.25 tesla . what is the current required in the conductor to create a force of 15N on the conductor ( 120A )
* Hey Bill .
 
Learning Curve :)

Part 1 : Scope . Object & Fundamental Characteristics
• An electric shock due to inadequate basic protection can be caused by
* Think about the definition of basic protection .
- The circuit protective conductor being touched under energisation .
- Touching the casing of a Class 11 portable drill .
- A person touching conduit under fault conditions .
- Brushing a Phase /Line conductor with your hand . ●

• IEE Regulations BS-7671 applies for
* What areas below do the Regulations cover .
- Electrical equipment on aircraft .
- Traction equipment .
- Fire alarms fed from a safety source .
- Construction sites . ● 110.1 Regs .

• Who is responsible for specifying the First periodic inspection on an installation .
* Who knows everything about an installation before the Other .
- The architect .
- The person responsible for the design . ●
- The electrical installer .
- The person ordering the work .

• An electric shock due to inadequate fault protection can be caused by
* Think about definition of fault protection .
- Accidental touching of a Phase/Line conductor .
- SELV terminals .
- Touching conduit under fault conditions . ●
- Class 11 equipment .

• An example of an exposed conductive part may be .
* exposed parts form part of an electrical system .
- Incoming lead water supply .
- Metalclad socket outlet cover ●
- An aluminium ceiling grid .
- A copper gas pipe .

• A single pole switch shall be connected in the
* If there’s only one pole . which is the most important .
- Earthing conductor only .
- Neutral conductor only .
- Across the neutral & Line conductor .
- Line conductor only . ●

• Class 11 equipment relies on basic insulation &
* Class 11 is also known as ►► Double Insulated .
- A circuit protective conductor .
- Supplementary insulation . ● Regs. p/21 . Read up .
- Bonded metal mechanical protection .
- Earthed equipotential bonding .
Remember : Class 11 equipment would provide . Basic & Fault Protection !!!!!!!!!!

• What is the maximum operating current for an RCD which may supply portable equipment used outdoors .
* Think about acceptable & common rated RCD.
- 20mA ) – 100mA ) – 10mA ) - 30mA ● )

• When designing an installation in licensed premises .
* There may be other factors to take into account .
- Additional statutory controls must be complied with ● 115.1.
- Drinking alcohol should be taken into account
- Consultation with the landlord should proceed the design proceed .
- Allowance should be made for future refurbishment .
 
• Basic protection protects .
* Against the most basic form of shock .
- Persons or livestock in contact with extraneous metalwork under fault conditions .
- Persons or livestock dismantling an item of electrical equipment .
- An unqualified person being allowed to work on electricity .
- Person or livestock touching a live conductor . ●

• A fireman’s emergency switch should be located .
* Think how the switch will be operated .
- 2.75m from the ground with the switches off position at the bottom .
- 2.75m from the ground with the switches off position at the Top . ● 537.6.4. (ii)
- 2m from the ground with the switches off position at the Top .
- 2m from the ground with the switches off position at the bottom .

• The electrical installation shall be designed for .
* Look in part 1 .
- The protection of persons & livestock .
- The protection of persons .
- The protection of persons . livestock & property .
- The functioning of an electrical installation & protection of persons . livestock & property . ● 131.1
( All the Words ) electrical installation : Safety persons : livestock & property : )

• When equipment is not covered by a known standard , the designer must confirm the same degree of safety as afforded by .
* A national fall back many items conform to .
- European Standards .
- Cenelec Standards .
- British Standards . ●
- IEC Standards .
 
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