Three phase
Three phase is a type of electricity supply with three live conductors, used by premises with heavier or larger equipment.
What it is
Most homes and many small units have a single-phase supply: one live conductor and a neutral. A three-phase supply has three live wires that share the load, which suits larger motors, lifts, commercial kitchens, workshops and bigger air conditioning. It lets more power be delivered more evenly.
Where you will see it
At the meter and main fuse. A three-phase installation usually has three main fuses at the cut-out, or a meter marked as three-phase, but supplies differ, so ask an electrician or your network operator to confirm. Bills and contracts may mention "3 phase". Find your meter details with our guide to finding your MPAN and MPRN.
Why it matters
Three-phase supplies are linked to larger supply capacity, so they may attract capacity charges and sometimes a half-hourly meter. If you add equipment, upgrading from single to three phase needs your network operator, takes time and costs money. See what a three-phase supply is for more.
Example
For three-phase, apparent power in kVA is about 1.732 × volts × amps per phase ÷ 1,000. At 415 V and 100 A per phase: 1.732 × 415 × 100 ÷ 1,000 = about 71.9 kVA. A single-phase 230 V supply at 100 A gives 230 × 100 ÷ 1,000 = 23 kVA, so the three-phase supply can carry roughly three times the load.
Do not work on supply cables or cut-outs yourself. Use a qualified electrician and your network operator.
Related terms
See kVA, reactive power and profile class.
Common questions on this topic
Sources
General information only. Energy prices, rules and supplier terms change; check the latest position with your supplier, Ofgem or the Energy Ombudsman before you act.