UK mains electricity standards
In the United Kingdom, nominal domestic voltage is 230V single-phase (+10% / −6%), and commercial supplies operate at 400V three-phase at a frequency of 50 Hz.
UK electricity billing is charged per kilowatt-hour (kWh), commonly referred to on utility bills as "units" of electricity.
Motors and industrial machinery with low power factors (below 0.95) often incur reactive power surcharges from UK Distribution Network Operators (DNOs), making power factor correction essential.
Worked example: Domestic UK electric shower
A typical 9.5 kW UK electric shower operating at 230V draws:
Current = 9,500 W ÷ 230 V ≈ 41.3 Amperes, requiring a dedicated 45A or 50A circuit breaker and 10 mm² cable.
A 15-minute shower consumes 9.5 kW × 0.25 h = 2.375 kWh (units).
Inputs for the UK electrical power calculator
Voltage and Current
Default 230V for UK domestic circuits or 400V for three-phase commercial machinery.
CALCULATOR QUESTIONS
UK 230V / 400V electrical power calculator questions
What is a "unit" of electricity in the UK?
One unit of electricity in the UK equals exactly one kilowatt-hour (1 kWh), which is 1,000 Watts running continuously for one hour.
What size fuse is needed for a 3 kW UK appliance?
At 230V, a 3,000 W load draws 3,000 ÷ 230 ≈ 13.04 Amperes, which operates on a standard UK 13A BS 1363 fused plug.