Live & Neutral Wires
Physics: Cambridge International GCSE Supplement, topic 4.10.2
Live & Neutral Wires
Wires
- A mains circuit in the UK consists of three wires: live (line), neutral, and earth.
- The live wire carries the alternating potential difference (about 230 V) from the mains supply.
- The neutral wire completes the circuit and is kept close to 0 V.
- The earth wire provides a low-resistance path to the ground if a fault occurs, preventing the appliance casing from becoming live.
Switch
- A switch is always placed in the live wire, not the neutral wire.
- This ensures that when the switch is off, no current can enter the appliance.
- If the switch were in the neutral wire, the appliance could still be connected to the live wire and remain dangerous even when “off”.
- Therefore, connecting the switch to the live wire ensures the circuit is safely disconnected from the mains supply.
Test yourself on Live & Neutral Wires
Which wire carries the alternating potential difference from the mains supply?
What is the main purpose of the earth wire in a mains circuit?
Why must a switch be connected to the live wire rather than the neutral wire?
What would happen if the switch were connected only to the neutral wire?
Which statement is true about the neutral wire?