The short answer: Single-phase power uses one alternating current at 230V and is the standard domestic and light commercial supply in the UK. Three-phase power uses three currents offset by 120 degrees, delivering 400V line-to-line. It is standard for industrial and large commercial premises because it supports higher loads, powers motors more efficiently, and distributes current more evenly across the supply.
Around 90% of the electrical energy consumed worldwide is generated and transmitted as three-phase power. For industrial and commercial premises, understanding which supply you have — and whether you need to upgrade — is fundamental to running equipment safely and efficiently.
Single-phase power is the standard electrical supply to homes and small businesses in the UK. It uses two conductors — a live and a neutral — carrying one alternating current that rises and falls in a single sine wave at 50Hz. The UK supply voltage is 230V single-phase. It is suitable for lighting, domestic appliances, and commercial equipment up to approximately 10kW. Above this load, three-phase supply becomes significantly more efficient and economical.
Three-phase power uses three live conductors, each carrying an alternating current offset by 120 degrees from the others. Because the three phases reach their peaks at different points in the cycle, the combined power delivery is smoother and more consistent than single-phase. In the UK, three-phase supply is 400V line-to-line (between any two phases) and 230V line-to-neutral (between any single phase and neutral). It is standard across industrial and large commercial premises.
| Factor | Single-Phase | Three-Phase |
|---|---|---|
| Number of conductors | 2 (live + neutral) | 3 live + neutral (4-wire) or 3 live only (3-wire) |
| UK supply voltage | 230V (live to neutral) | 400V line-to-line / 230V line-to-neutral |
| Power delivery | Pulsating — power dips to zero twice per cycle | Smooth and continuous — three overlapping phases |
| Typical capacity | Up to ~10–15kW practical maximum | Tens to hundreds of kW depending on supply fuse rating |
| Motor compatibility | Single-phase motors only; less efficient above 3kW | Three-phase motors — more efficient, longer-lasting, no starting capacitors needed |
| Typical applications | Homes, small offices, light commercial, small workshops | Factories, industrial plant, CNC machinery, welding equipment, large HVAC, EV chargers |
| Installation cost | Lower — standard supply, no upgrade required | Higher if upgrading from single-phase; DNO application required |
| Running cost at high loads | Higher — less efficient for large motor loads | Lower — more efficient power distribution above ~3kW |
| Cable sizing | Larger cables needed to carry equivalent load | Smaller cables for the same total load — current split across three phases |
| UK standard | BS 7671 (IET Wiring Regulations) | BS 7671 (IET Wiring Regulations) |
| Who supplies it | Standard DNO connection | Available from DNO on application — most industrial sites already connected |
Yes — but it requires an application to your local Distribution Network Operator (DNO) and a new supply installation by a qualified NICEIC or ECA registered electrical contractor. The DNO will assess whether three-phase supply is available at the local network and what connection works are required. Costs vary significantly depending on proximity to the nearest three-phase network. Varlowe's electrical team can advise on the process and carry out the internal installation work.
Varlowe Industrial Services provides NICEIC-registered electrical services including fixed wire testing, industrial electrical installations, and three-phase power supply upgrades. Contact us to discuss your requirements.
Single-phase power uses two conductors (live and neutral) and delivers power in a single alternating current wave at 230V in the UK. Three-phase power uses three live conductors carrying alternating currents 120 degrees apart, delivering 400V line-to-line. Three-phase is standard for commercial and industrial premises because it supports higher loads and powers electric motors more efficiently.
In the UK, three-phase power is supplied at 400V between phases (line-to-line) and 230V between each phase and neutral (line-to-neutral). Single-phase supply is 230V. Three-phase is available from the distribution network to commercial and industrial premises that require it.
Three-phase power is required when running equipment with motors above approximately 3–4kW, such as CNC machines, industrial welders, compressors, lifts, and large HVAC systems. Most commercial and industrial buildings are already supplied three-phase. If single-phase is the current supply and you need to add significant motor loads, a three-phase upgrade will be required.
Yes, but it requires an application to your distribution network operator (DNO) and an electrical installation upgrade by a qualified contractor. The DNO will assess whether three-phase supply is available at the local network and what connection works are required. A NICEIC-registered contractor should design and install the upgraded internal distribution system.
Yes, for high-load and motor-driven applications. Three-phase motors are inherently more efficient than equivalent single-phase motors — they have higher power factors, no starting capacitors, and more consistent torque output. For loads above approximately 3kW, three-phase supply requires smaller cable cross-sections to carry the same total power, reducing installation cost and cable losses.