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Flashcards in Domestic Electricity Deck (81):

what are two potential dangers of mains electricity?

electrocution (can cause death)

can start a fire (can cause death)


what are some hazards (5) of domestic electricity?

touching frayed electrical cables

long or overheating cables

damaged or incorrectly wired plugs

allowing water or wet objects to enter plug sockets or touch frayed cables

pushing metal objects into plug sockets


label this diagram of a 3-pin plug


what is a conductor?

a material which allows charge to move easily through it


what is current?

moving electric charges, for example, electrons moving through a metal wire


define electrocute

cause injury or death by an electric shock


what is a fuse?

an electrical component that protects circuits and electrical devices from overload by melting when the current becomes too high


what is an insulator?

material that does not allow charge or heat to pass through it easily


define potential difference

the potential difference (or voltage) of a supply is a measure of the energy given to the charge carriers in a circuit, units volts (V)


define resistance

the opposition in an electrical component to the movement of electrical charge through it

resistance is measured in ohms


what are the three wires in a plug?

the neutral wire

the live wire

the earth wire


what colour is the live wire?



what colour is the neutral wire?



what colour is the earth wire?

green and yellow stripes


what is the function on the live wire?

provides the path along which the electrical energy from the power station travels

this wire is alternately positive and negative causing alternating current (ac) to flow along it

held at a voltage of 230 V


what is the function on the neutral wire?

completes the circuit


what is the function on the earth wire?

usually has no current flowing through it

a safety wire to stop the appliance becoming live - protects you if an appliance develops a fault


What do each of the three wires have at their core?

each have a core of copper as it is a good conductor of electricity


what do each of the three wires have as their outer layers?

each has an outer layer of flexible plastic as plastic is a good electrical insulator


what position is the live wire in the plug?

on the right


what position is the neutral wire in the plug?

on the left


what position is the earth wire in the plug?

on the top


how do you remember the position of the three wires in the plug?

blue (neutral) goes left

brown (live) goes right

striped (earth) goes to the top


what are the feautures (5) of a plug?

the case is made from tough plastic or rubber, because these materials are good electrical insulators

the three pins are made from brass, which is a good conductor of electricity

there is a fuse between the live terminal and the live pin

the fuse breaks the circuit if too much current flows

the cable is secured in the plug by a cable grip - this should grip the cable itself, and not the individual wires inside it


what are the pins in the plug made of? why?


it is a good conductor of electricity


what is the case of the plug, the cable grip and cable insulation made of? why?

tough plastic or rubber

these materials are good electrical insulators


what position is the fuse in the plug?

between the live terminal and the live pin


what is the purpose of a fuse?

fuses protect electrical circuits and appliances

works in conjunction with the earth wire to ensure safety as the fuse is a wire that melts and breaks the circuit when too much current flows through it


what is double insulation?

a casing made from an insulator such as plastic


why don't appliances with double insulation require earthing?

they have plastic casings, or they have been designed so that the live wire can not touch the casing. As a result, the casing cannot give an electric shock, even if the wires inside become loose

use a two-wire flex so they do not need an earth wire


what is the symbol for double insulation?


give some examples (2) of double insulated appliances

vacuum cleaners

electric drills


is there an "outer metal casing" in double insulation?



is there an "outer metal casing" in single insulation?



how many layers of insulation are there in double insulation?



give some examples (3) of electrical appliances with an "outer metal casing"


washing machines




live wire touches the "outer metal casing", the ... wire provides ...

live wire touches the "outer metal casing", the earth wire provides safe route for the current to flow through


what will happen if the live wire inside an appliance comes loose and touched the metal casing?

you will get an electric shock


why does a strong current surges through the earth wire when the live wire inside an appliance comes loose and touches the metal casing?

the earth wire because it has a very low resistance


what is the earth wire in your home in contact with?

the earth


what is the purpose of insulation?

covers the live wire with a material that won't conduct the electricity


what is the danger of a damaged plug?

an cause a spark which can cause a fire

 the exposed wires could also expose you to an electric shock


what is the danger of water around sockets?

water can conduct electricity and it provides a conducting path for a large current to flow

it could electrocute you if you were to touch it


what is the danger of pushing metal objects into sockets?

metal conducts electricity



how does the earth wire work together with the fuse to make sure faulty appliances are safe?

if a fault occurs in the live wire, the live wire touches the outer metal casing of theapplaince

the current now flows from the live wire through the outer metal casing and down the earth wire

the earth wire is at OV and the current, which has a high voltage, tried to find the path of low resistance to the ground to be earthed. this cicuit has a low resistance as there is no heating element (has a high resistance). the other circuit has a higher resistance 

the current increases dramatically so the fuse wire melts (heating effect) and breaks the cicuit so you cannot be electrocuted

the appliance no longer works


what is the heating effect?

if current is too high the temperature increases and the fuse melts


what is the equation for power?

power = current x voltage

P = IV


rearrange the power equation so that current is the subject

curent = power ÷ voltage

I = P ÷ V


rearrange the power equation so that voltage is the subject

voltage = power ÷ current

V = P  ÷ I


what is power measured in?

watts (W)


what is voltage measured in?

volts (V)


what is current measured in?

amperes (amps)


Use V = E ÷ Q and Q = It to prove E=ItV

V = E÷It so E = ItV


what equation links energy, current, time and voltage?

energy = current x time x voltage

E = I x t x v


what is an easy way to remember the equation that links energy, current, time and voltage?

Itv the tv channel

E = ItV


if E = ItV, how can P = IV?

E = ItV

power = work/energy (E) ÷ time

power = ItV ÷ t

power = IV


A kettle has a power rating of 2000W and is plugged into the mains (230V)

Calculate the current flowing through the kettle

P = IV so I = P ÷ V

= 2000 ÷ 230

= 8.66 (2 d.p) amps


Which size fuse should be fitted if the current is 8.66 (2 d.p) amps

choice: 3A, 5A, 13A

13 A


which size fuse should you always choose?

the bigger size

e.g. 1A = choose 3A

e.g. 4A = 5A

e.g. 9A = 13A


what are the three standard choices of fuses?





what size fuse should you choose if the current is 5A ?



A lamp has 60W bulb and is plugged into the mains (230V) Calculate the curent flowing through the lamp

P = IV so I = P ÷ V

= 60 ÷ 230

= 0.26 (2 d.p) amps


what is one of the most powerful devices in the home?

the kettle


in a home, there is nothing bigger than ... that you can plug in


in a home, there is nothing bigger than 3000W that you can plug in

the fuse would break


if the power of one of your appliances exceeds 3000W, e.g. an electrical oven (7000W), where do you connect it to?

connect it directly to the mains


what is the purpose of circuit breakers?

protect electrical circuits and appliances


what do circuit breakers do to fulfil their purpose?

 they detect faults and then stop the flow of electricity


residual current circuit breakers (RCCBs) protect ... circuits


residual current circuit breakers (RCCBs) protect some circuits


how do residual current circuit breakers protect some circuits?

they detect a difference in the current between the live and neutral wires


what workes faster, a fuse or a residual current circuit?

a residual current circuit


what could happen if the plug is damaged?

the live parts could be exposed and you could get a shock


what could happen if the cable is frayed?

the live parts might be uncovered


wht is the danger of the cable being too long for the appliance?

they could be a trip hazard


why should you never push a metal into a plug socket (unless its the pins of a plug)?

metals conduct electricity so you could get a shock


why should you check that there's no water near electrical objects?

water is a very good conducter of electricity so you could get a shock


Briefly: how does earthing and fuses prevent fire and shocks?

If a fault develops in which the live wire somehow touches the metal case, then because the case is earthed, a big current flows in through the live wire, through the case and out the earth wire

This surge in current 'blows' (melts) the fuse (or trips the circuit breaker) which cuts off the live supply

This isolates the whole appliance, making it impossible to get an electric shock from the case. It also prevents the risk of fire caused by the heating effect of a large current


what are circuit breakers?

Circuit breakers are an electrical safety device used in some circuits. Like fuses, they protect the circuit fro, damage if too much current flows


How do circuit breakers work?

When circuit breakers detect a surge in current in a circuit, they break the cicuit by opening a switch


circuit breakers act as ... fuses

circuit breakers act as resettable fuses


How do Residual Current Circuit Breakers work?

Normally exactly the same current flows through the live and neutral wires

If somebody touches the live wire, a small but deadly current will flow through them to the earth. This means the neutral wire carries less current than the live wire

The RCCB detects this difference in current and quickly cuts off the power by opening a switch


What are advantages of circuit breakers (including Residual Current Circuit Breakers) over fuses?

A circuit breaker (and the circuit they're in) can easily be reset by flicking a switch on the device. This makes them more convenient than fuses - which have to be replaced once they've melted

Residual Current Circuit Breakers (RCCBs) operates much faster than fuses - they break the circuit as soon as there is a current surge - no time is wasted waiting for the current to melt a fuse. This makes them safer

RCCBs even work for small current changes that might not be large enough to melt a fuse. Since even small current changes could be fatal, this means RCCBs are more effective at protecting against electrocution