***Useful Information for Apprentices***

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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 ) ,

 

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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 ) ,

 

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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 ,

 

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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 ,

 

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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 ,

 

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( 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 ,

 

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● 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 ,

 

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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

 

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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 , ♫♫♫

 

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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 ,

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 ,