***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 ,

 

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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 ,

 

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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 )

 

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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 )

 

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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.

 

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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 ,

 

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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.

 

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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.

 

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411 , Protective Measure : Automatic Disconnection of Supply , “ ADS “

 

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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 ..

 

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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