***Useful Information for Apprentices***

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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