The live wire carries the alternating current from the mains supply to the appliance. It is coloured brown in UK and Malaysian wiring. The live wire alternates between approximately +325 V and -325 V (giving an RMS value of 230 V).
Why the live wire is dangerous
The live wire has a large potential difference relative to earth (the ground beneath your feet is at 0 V). If you touch the live wire while standing on the ground, current flows through your body to earth. This can cause:
- Burns at the entry and exit points.
- Disruption of the electrical signals that control your heart (potentially fatal).
- Muscle contractions that prevent you from letting go.
The live wire is dangerous even when the appliance is switched off, as long as the plug is in the socket. The switch should always be on the live wire side of the circuit so that no part of the appliance is live when the switch is off.
The live wire in a plug
In a three-pin plug, the live wire connects to the fuse. This is important: if the fuse is on the neutral wire instead, the appliance remains live even after the fuse blows, which is a safety hazard.
Fuse and live wire
The fuse is always connected in series with the live wire. If the current exceeds the fuse rating, the fuse melts and breaks the circuit. The circuit breaker performs the same function but can be reset without replacement.
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