Three-Phase Power
A higher-capacity electrical supply that delivers power through three alternating currents, used in homes with large electrical demands such as heat pumps, EV chargers, or commercial-grade equipment.
Three-phase power is a type of electrical supply that delivers electricity through three separate conductors, each carrying an alternating current offset in phase from the others. It provides roughly three times the power capacity of a standard single-phase supply, making it suitable for homes or buildings with high electrical demands.
Three-phase vs. single-phase
Most homes in the UK and US have a single-phase supply, which is sufficient for typical household loads — lighting, standard sockets, a cooker, a shower, and a boiler.
A three-phase supply becomes necessary when the total electrical demand exceeds what a single-phase supply can provide:
| Feature | Single-phase | Three-phase |
|---|---|---|
| Typical capacity (UK) | Up to ~23 kW (100A) | Up to ~69 kW (100A per phase) |
| Typical capacity (US) | Up to ~24 kW (200A) | Up to ~48 kW+ |
| Common in | Most homes | Large homes, commercial, rural |
| Cost | Standard | Higher connection and running costs |
When three-phase power comes up in a renovation
- Large properties — a big house with multiple bathrooms, a large kitchen, electric heating, and an EV charger may exceed the capacity of a single-phase supply
- Heat pumps — larger air-source or ground-source heat pumps often require a three-phase supply
- Commercial equipment — if you are converting a commercial building to residential (a barn conversion, for example), it may already have three-phase power
- Workshops and outbuildings — large power tools, welders, or kilns may need three-phase power
- Rural properties — some rural areas only have three-phase supplies available
Getting a three-phase supply
If your renovation requires more power than your existing single-phase supply can deliver, you can apply to your electricity distribution network operator (DNO) for an upgrade:
- Cost — upgrading from single-phase to three-phase involves new cabling from the street to your property and a new meter. Costs vary significantly (thousands, not hundreds), depending on the distance from the nearest three-phase supply point
- Timescale — applications can take weeks to months, so plan early
- Consumer unit — a three-phase supply requires a compatible three-phase consumer unit or distribution board
Practical tip
If you are planning a major renovation with significant electrical demands — especially if you are adding a heat pump, EV charging, or converting a large property — ask your electrician to carry out a maximum demand calculation early in the design process. This determines whether your existing single-phase supply is sufficient or whether a three-phase upgrade will be needed. Knowing this early avoids expensive redesigns later. Discuss the findings with your contractor so it can be factored into the scope of work and timeline.