Single-phase vs three-phase supply

What it is

The UK electricity grid is three-phase, but the way it reaches each home varies. Most UK domestic properties have a single-phase connection: one live wire, one neutral, one earth, with a typical fuse rating of 60-100A. A minority of properties (larger homes, rural locations, some flats and new-build estates) have three-phase: three live wires offset by 120 degrees, one neutral, one earth, providing roughly three times the capacity.

Single-phase delivers around 24kW maximum at 100A. Three-phase delivers around 69kW across three 100A phases, but each phase can carry only its individual current rating. Most home loads (lights, sockets, kettles) draw from a single phase even on a three-phase installation; the phases are balanced across circuits.

Which do you have

The fastest way to tell is to look at the meter and head fuse. A single-phase supply has one live cable entering the cut-out (typically marked 100A or 60A); three-phase has three. The consumer unit on a three-phase supply will have either three separate split units or a single three-phase consumer unit with three-pole RCDs.

If you are uncertain, the safest method is to ask your DNO (distribution network operator). They can confirm the supply type by your address. Find your DNO by postcode at the Energy Networks Association lookup.

Why it matters for home energy

Single-phase supply has a typical maximum import and export capacity around 17-25kW depending on the head fuse. Beyond that, the DNO is unlikely to approve additional generation or load without an upgrade.

• Solar: single-phase inverters in the UK are typically capped at 3.68kW for fast-track G98 notification; over that, full G99 application is required. A three-phase supply allows up to 16A per phase (around 11kW total) under G98.
• Battery: hybrid inverters paired with a single-phase supply are common up to around 5-6kW; three-phase opens larger options.
• EV charging: single-phase home chargers are limited to 7.4kW. Three-phase chargers can deliver up to 22kW, useful for high-mileage households or shared chargers.
• Heat pumps: most domestic ASHP installs run fine on single-phase. Large ASHPs (above 16kW) or GSHPs in larger homes sometimes need three-phase.

Upgrading to three-phase

Upgrading is possible but disruptive and not always quick. Costs range from £500 to £2,000 for properties where a three-phase main cable already passes nearby, up to £5,000-£15,000+ if a new connection or substation work is needed. Lead times of 12-26 weeks are common.

It rarely makes sense to upgrade purely for one piece of kit. If two or three of the following apply, the case strengthens: multiple high-power loads (EV charger + heat pump + electric cooking), solar generation above 5kW, planning permission for additional generation, or sharing a property with another household.