***Useful Information for Apprentices***

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“ General Health and Safety at Work “

Question 1.1
What do the letters CDM stand for ?
A: Control of Demolition and Management Regulations
B: Control of Dangerous Materials Regulations
C: Construction (Demolition Management) Regulations
D: Construction (Design and Management Regulations ) Answer: D )
Question 1.2
Identify one method of enforcing regulations that are
available to the Health and Safety Executive:
A: Health Notice
B: Improvement Notice
C: Obstruction Notice
D: Increasing insurance premiums
Answer: B Improvement notices require action to achieve standards which meet health and safety law :
Question 1.3
What happens if a Prohibition Notice is issued by an
Inspector of the local authority or the HSE ?
A: The work in hand can be completed, but no new work started
B: The work can continue if adequate safety precautions are put in place
C: The work that is subject to the notice must cease
D: The work can continue, provided a risk assessment is carried out,
Answer: C The work covered by a prohibition notice must cease until the identified danger is removed.
Question 1.4
Health and Safety Executive Inspector can ?
A: Only visit if they have made an appointment
B: Visit at any time
C: Only visit if accompanied by the principal contractor
D: Only visit to interview the site manager
Answer: B Inspectors have a range of powers, including the right to visit premises at any time.
Question 1.5
A Prohibition Notice means:
A: When you finish the work you must not start again
B: The work must stop immediately
C: Work is to stop for that day only
D: Work may continue until the end of the day
Answer: B The work activity covered by the prohibition notice must cease, until the identified danger is removed ,
Question 1.6
In what circumstances can an HSE Improvement Notice be issued ?
A: If there is a breach of legal requirements
B: By warrant through the police
C: Only between Monday and Friday on site
Answer: A Improvement notices require action to achieve standards which meet health and safety law .
Question 1.7
What is an “Improvement Notice”?
A: A notice issued by the site principal contractor to tidy up the site
B: A notice from the client to the principal contractor to speed up the work
C: A notice issued by a Building Control Officer to deepen foundations
D: A notice issued by an HSE/local authority Inspector to enforce compliance with health
Answer: D Improvement notices require action to achieve standards which meet health and safety law .
Question 1.8
If a Health and Safety Executive Inspector issues a“ Prohibition Notice”, this means that:
A: the Site Manager can choose whether or not to ignore the notice
B: specific work activities, highlighted on the notice, must stop
C: the HSE must supervise the work covered by the notice
D: the HSE must supervise all work from then on
Answer: B Prohibition notices are intended to Stop activities which can cause serious injury.
Question 1.9
Which one of the following items of information will you find on the Approved Health and Safety Law poster?
A: Details of emergency escape routes
B: The location of the local HSE office
C: The location of all fire extinguishers
D: The identity of the first aiders
Answer: B The poster also lists the persons with health and safety responsibilities, but not first aiders.
Question 1.10
Who is responsible for signing a Company Safety Policy ?
A: Site Manager
B: Company Safety Officer
C: Company Secretary
D: Managing Director
Answer: D The Health and Safety at Work Act requires the most senior member of management to sign the health and safety policy
statement.

Question 1.11
Which one of the following must be in a company’s written Health and Safety Policy:
A: Aims and objectives of the company
B: Organisation and arrangements in force for carrying out the health and safety policy
C: Name of the Health and Safety Adviser
D: Company Director’s home address
Answer: B This requirement appears in the Health and Safety at Work Act.
Question 1.12
Employers have to produce a written Health and Safety Policy statement when:
A: A contract commences
B: They employ five people or more
C: The safety representative requests it
D: The HSE notifies them
Answer: B This is a specific requirement of the Health and Safety at Work Act.
Question 1.13
Companies employing five or more people must have a written Health and Safety Policy because:
A: The principal contractor gives them work on site
B: The HSAWA 1974 requires it
C: The Social Security Act requires it
D: The trade unions require it
Answer: B
Question 1.14
What do the letters HSC stand for ?
A: Health and Safety Contract
B: Health and Safety Consultant
C: Health and Safety Conditions
D: Health and Safety Commission Answer: D
Question 1.15
Which ONE of the following statements is correct ? The Health and Safety Executive is:
A: a prosecuting authority
B: an enforcing authority
C: a statutory provisions authority
Answer: B The Health and Safety Executive enforces health and safety legislation.
Question 1.16
The Health and Safety at Work Act requires employers to provide what for their employees?
A: Adequate rest periods
B: Payment for work done
C: A safe place of work
D: Suitable transport to work
Answer: C This is a specific requirement of Section 2 of the Health and Safety at Work Act.
Question 1.17
The Health and Safety at Work Act 1974 and any regulations made under the Act are:
A: Not compulsory, but should be complied with if convenient
B: Advisory to companies and individuals
C: Practical advice for the employer to follow
D: Legally binding Answer: D
Question 1.18
Under the Health and Safety at Work Act 1974, which of the following have a duty to work safely?
A: Employees only
B: The general public
C: Employers only
D: All people at work
Answer: D Employers, employees and the self-employed all have a duty to work safely under the Act.
Question 1.19
What is the MAXIMUM penalty that a Higher Court, can currently impose for a breach of the Health and Safety at Work Act?
A: £20,000 fine and two years imprisonment
B: £15,000 fine and three years imprisonment
C: £1,000 fine and six months imprisonment
D: Unlimited fine and two years imprisonment
Answer: D A Lower Court can impose a fine of up to £20,000 and/or up to six months imprisonment for certain offences. The potential fine in a Higher Court, however, is unlimited and the term of imprisonment can be up to 2 years.
Question 1.20
What do the letters ACoP stand for ?
A: Accepted Code of Provisions
B: Approved Condition of Practice
C: Approved Code of Practice
D: Accepted Code of Practice
Answer: C An ACOP is a code of practice approved by the Health and Safety Commission.

Question 1.21
Where should you look for Official advice on health and safety matters?
A: A set of health and safety guidelines provided by suppliers
B: The health and safety rules as laid down by the employer
C: Guidance issued by the Health and Safety Executive
D: A professionally approved guide book on regulations
Answer: C The HSE is the UK enforcing body and its guidance can be regarded as ‘official’
Question 1.22
Regulations that govern health and safety on construction sites:
A: apply only to inexperienced workers
B: do not apply during ’out of hours’ working
C: apply only to large companies
D: are mandatory ( that is, compulsory )
Answer: D The requirements of health and safety law are mandatory, and failure to follow them can lead to prosecutions.
Question 1.23
Which of the following statements is correct ?
A: The duty for health and safety falls only on the employer
B: All employees must take reasonable care, not only to protect themselves but also their colleagues
C: Employees have no responsibility for Health and Safety on site
D: Only the client is responsible for safety on site
Answer: B The responsibility for management of Health and Safety Act at Work rests with the employer
Question 1.25
Which of the following is correct for risk assessment?
A: It is a good idea but not essential
B: Only required to be done for hazardous work
C: Must always be done
D: Only required on major jobs
Answer: C There is a legal requirement for all work to be suitably risk assessed.
Question 1.26
In the context of a risk assessment, what do you understand by the term risk?
A: An unsafe act or condition
B: Something with the potential to cause injury
C: Any work activity that can be described as dangerous
D: The likelihood that harm from a particular hazard will occur
Answer: D Hazard and risk are not the same. Risk reflects the chance of being harmed by a hazard
Question 1.27
Who would you expect to carry out a risk assessment on your working site?
A: The site planning supervisor
B: A visiting HSE Inspector
C: The construction project designer
D: A competent person
Answer: D A risk assessment must be conducted by a 'competent person’.
Question 1.28
What is a HAZARD ?
A: Where an accident is likely to happen
B: An accident waiting to happen
C: Something with the potential to cause harm
D: The likelihood of something going wrong
Answer: C Examples of hazards include: a drum of acid, breeze blocks on an elevated plank; cables running across a floor.
Question 1.29
What must be done before any work begins ?
A: Emergency plan
B: Assessment of risk
C: Soil assessment
D: Geological survey
Answer: B This is a legal requirement of the Management of Health and Safety at Work Regulations.
Question 1.30
Complete the following sentence: A risk assessment
A: is a piece of paper required by law
B: prevents accidents
C: is a means of analysing what might go wrong
D: isn’t particularly useful
Answer: C Risk assessment involves a careful review of what can cause harm and the practical measures to be taken to reduce the risk of harm.

 

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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 ,

 

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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.

 

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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 ,