chapter 18 - practical electricity

Question 1

live wire and its colour

Answer 1

brown

wire connected to high potential

Question 2

neutral wire

Answer 2

blue

wire connected has zero voltage

Question 3

earth wire

Answer 3

yellow and green

low resistance, allows excess current flowing into earth preventing electric shock

Question 4

ring mains

Answer 4

there are two paths the current can take in the live wire and also in the neutral wire. this means that it is possible to use at one time twice as much current as could be taken with a single wire

Question 5

three pin plug

Answer 5

from top to bottom, left to right : earth, neutral and live wire

Question 6

fuse

Answer 6

safety device inserted into an electrical circuit to protect the equipment and wiring from excessive current flow

made of a thin wire with low melting point connected in a circuit to break the flow of current if current exceeds its specified value (fuse rating)

always connected to live wire. if fuse is placed at the neutral wire, the appliance is connected to the live wire and will be “live”. when coming in contact with metal casing of appliance, hand forms a closed circuit and there is a risk of electrocution. however, if fuse is connected to the live wire, the fuse will melt if a large current flows through

Question 7

switch

Answer 7

used as safety device to cut off current flow whenever there is a potential electrical hazard

all switches have to be connected to live wire . if switch is placed at the neutral wire, the appliance is connected to the live wire and will be “live”. when coming in contact with metal casing of appliance, hand forms a closed circuit and there is a risk of electrocution. however, if switch is connected to the live wire, when the switch is off, the live wire is effectively at zero potential like the neutral wire

Question 8

earth wire prevention of hazard

Answer 8

sometimes, the live wire might come loose and come into contact with any metal part of the appliance, causing it to be “live”. when someone touches the metal part, it forms a closed circuit and the current flow through the person’s hand into their body, causing them to be electrocuted. however, with an earth wire, the current will flow into the ground and not come into contact with the metal casing

Question 9

why is it safe to use two pin plugs

Answer 9

• outer casing completely amde of plastic
• insulator covering the live and neutral wires (doube insulation)

Question 10

what happens when there is damaged insulation

Answer 10

with the live wires exposed, a person touching it may get electrocuted which might be fatal
the live and neutral wires might come into contact and cause a short circuit, reuslting in a large current flowing through the wires. overheating follows which might cause a fire

Question 11

what happens when there is an overheating of cables

Answer 11

when sockets are overloaded using extension plugs, it might get overheated if the current flowing through exceeds the current rating, damaging the insulation of the cable