Electric Voltage

The potential difference that pushes current around a circuit.

What it is

Voltage (U or V) is measured in volts. In the UK the nominal single-phase supply voltage to earth (U0) is 230 V and the three-phase line voltage is 400 V, with permitted tolerance of +10% / −6%.

Voltage bands

BS 7671 Part 2 defines Band I (extra-low voltage, not exceeding 50 V AC / 120 V ripple-free DC) and Band II (low voltage, above ELV up to 1000 V AC / 1500 V DC).

Key regulations

Part 2 DefinitionsAppendix 2