electrical safety Flashcards
what is a fuse
a fuse is a safety device designed to cut off the flow of electricity to an appliance if the current becomes too large.
what is the symbol of a fuse
a rectangle with a line going through it
what do fuses usually consist of
a glass cylinder containing a thin metal wire.
what happens if the current in the wire becomes too large
the wire heats up and melts. this causes the wire to break, breaking the circuit and stopping the current.
what happens if the live wire come in contact with the case?
the case would become electrified and anyone would would touch it would become electrocuted.
what is an earth wire?
its an additional safety wire that reduces the risk of the live wire coming in contact with the case and electrifying it.
what are the names of the three wires that go into a mains powered appliance?
live, neutral and earth wire.
what happens when the live, neutral and earth wire go into a mains powered appliance?
1) provides a low resistance path to the earth
2) this causes surge of current in the earth wire and hence also in the live wire.
3) The high current through the fuse causes it to melt and break.
4) This cuts off the supply of electricity to the appliance, making it safe.
what is meant by the term ‘an appliance is double insulated’
appliances with no metal cases so theres no risk of them becoming electrified. (they have two layers of insulation)
what are the two layers of insulation?
1) insulation around the wires
2) the non metallic case acts as a second layer of insulation.
what is the symbol of a double insulated wire.
a square box around a square box. (they do not require earth wires)
