Physics – 4.4 Electrical safety | e-Consult

When a switch is connected to the live wire in a mains circuit, the flow of electricity is interrupted when the switch is turned off. Electricity flows from the live wire, through the device, and back to the neutral wire. The earth wire provides a safety path for electricity in the event of a fault, ensuring that the metal parts of appliances do not become live.

If the switch were connected to the neutral wire, the circuit would be broken when the switch is turned off, but the live wire would still be connected to the device. This means that a live voltage would still be present on the metal casing of the appliance. If someone were to touch the appliance, they could receive a dangerous electric shock. The earth wire provides a low-resistance path back to the source, causing a large current to flow and tripping the circuit breaker or fuse, thus disconnecting the power. Therefore, connecting the switch to the live wire ensures that the path for the safety current (through the earth wire) is always maintained when the switch is off, preventing a potentially lethal live voltage on the appliance casing.