***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

 

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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.

 

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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.

 

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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.

 

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* 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 )

 

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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

 

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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 ,

 

[brucelee]

Thanks mr leaf
great work will be a great help

 

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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 ,

 

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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.

 

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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

 

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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 ,

 

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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.

 

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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.

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.

 

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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 ,

 

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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 )

 

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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

 

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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 ,

 

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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 ,

 

[amberleaf]

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.