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P2.5 Mains Electricity


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Live wire
The wire of a mains circuit that has a potential that alternates from positive to negative and back each cycle.
Alternating Current
Electric current in a circuit that repeatedly changes direction.
Earthed
Connected to the ground by means of a conducting lead or wire.
Fuse
This contains a thin wire that melts and cuts the current off if too much current passes through it.
Frequency of an alternating current
The number of complete cycles an alternating current passes through each second. The unit of frequency is the hertz (Hz).
Circuit breaker
An electromagnetic switch that opens and cuts the current off if too much current passes through it.
Cable
Two or three insulated wires surrounded by an outer layer of rubber of flexible plastic.
Direct Current
Electric current in a circuit that is in one direction only.
Neutral wire
The wire of a mains circuit that is earthed at the local sub-station so its potential difference is close to zero.
Oscilloscope
A device used to display the shape of an electrical wave.
RCCB Residual Current Circuit Breaker
This cuts off the current in the live wire when it is different from the current in the neutral wire.
Socket
This is used to connect the mains plug of a mains appliance to the mains circuit.
Three pin plug
This has a live pin, a neutral pin and an earth pin. The earth pin is used to earth the metal case of an appliance so the case cannot become live.
Time base control
An oscilloscope control used to space the waveform out horizontally.
Plug
This has an insulated case and is used to connect the cable from an appliance to a socket.