Business Energy Glossary
What is a single-phase supply?
A single-phase supply is the basic UK electricity supply configuration. Power is delivered through one live conductor and one neutral, at a nominal voltage of 230 V. Single-phase is the standard for domestic premises, small offices, retail units, and any commercial site with modest power requirements. The maximum capacity of a typical single-phase supply is around 23 kW (100 A at 230 V), beyond which a three-phase supply is required.
Single-phase covers the majority of UK electricity supplies by count but only a smaller share of total consumption. Most commercial sites with significant equipment, multiple appliances running simultaneously, or any three-phase equipment will need to upgrade to three-phase. Understanding the limits of single-phase is essential when planning new equipment installations or business expansion.
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How single-phase works
A single-phase electricity supply delivers power through one alternating current waveform, varying at 50 Hz. The supply consists of three conductors: one live carrying the AC waveform, one neutral providing the return path, and one earth for protective grounding.
The nominal voltage between live and neutral is 230 V in the UK. The actual voltage may vary within a permitted range (+10/-6 per cent under BS EN 50160), so the supply could measure anywhere from 216 V to 253 V at any given moment.
Capacity of a single-phase supply
The capacity of a single-phase supply is determined by the rating of the cut-out fuse installed by the DNO. Standard ratings:
| Cut-out fuse rating | Maximum power | Typical use |
|---|---|---|
| 60 A | ~13.8 kW | Older domestic, small flats |
| 80 A | ~18.4 kW | Larger domestic, very small commercial |
| 100 A | ~23.0 kW | Standard new commercial single-phase |
The maximum power assumes the supply runs at full capacity continuously, which is rare. In practice the supply can handle short-duration peaks above the nominal rating but the long-term average must stay within the cut-out fuse limit. Sustained over-current trips the fuse and disconnects the supply.
When single-phase is suitable
Single-phase is sufficient for any commercial site where:
- Peak demand stays comfortably below 100 A (around 23 kW).
- No equipment requires three-phase power (most lighting, sockets, small appliances are single-phase).
- No high-power motors, large air conditioning units, or rapid EV chargers are present.
- The site is unlikely to expand its electrical load significantly.
Typical single-phase commercial sites: small offices, retail units, salons, takeaways, small cafes, and most retail high-street businesses.
Limits of single-phase
A single-phase supply hits its limits at three points:
- Total simultaneous load. Multiple high-power appliances running at the same time (kettles, ovens, air conditioning, dishwashers) can exceed the cut-out rating, particularly on 60 A or 80 A supplies.
- Three-phase equipment. Large air conditioning, commercial refrigeration, lifts, industrial motors, and rapid EV chargers above 7 kW require three-phase power. They cannot be operated on single-phase.
- Network voltage drops. Long single-phase runs can have significant voltage drop under load. Three-phase distributes the load across three conductors, reducing the drop for the same total power.
Cost of a single-phase supply
Single-phase supplies have lower fixed costs than three-phase:
- Lower standing charge. Single-phase meters and connections cost less to install and maintain.
- Lower meter operation fee. Single-phase MOP and DC fees are typically half of equivalent three-phase fees.
- Lower new connection charge. Where a new supply is being installed, single-phase is significantly cheaper than three-phase.
The unit rate per kWh is generally the same on single-phase and three-phase contracts. Energy consumed costs the same per kWh; the fixed elements differ.
Upgrading to three-phase
If the site outgrows its single-phase supply, an upgrade to three-phase is required. The process:
- Apply to the DNO through the supplier or directly. Specify the new capacity required in kVA.
- Receive a quotation covering the connection work, any network reinforcement, and the new meter installation.
- Accept and pay. Typical lead time: 4 to 12 weeks for urban sites, longer for rural sites needing reinforcement.
- Civil works completed by the DNO. Internal wiring upgrade is the customer responsibility.
- New three-phase meter installed by the supplier-appointed MOP. Supply energised.
Cost ranges from a few thousand pounds for a simple urban upgrade to tens of thousands for rural sites requiring substantial new infrastructure. The standing charge on the new three-phase supply will be higher than the previous single-phase, reflecting the more complex connection.
a single-phase supply FAQs
What is a single-phase electricity supply?
The basic UK electricity supply with one live conductor and one neutral, delivering 230 V at the customer side. Standard for homes and small commercial premises with modest power requirements.
How much power can a single-phase supply deliver?
Up to around 23 kW (100 A at 230 V) for the standard new commercial single-phase. Older supplies with 60 A or 80 A cut-outs deliver less (around 14 to 18 kW).
When do I need to upgrade to three-phase?
When peak demand exceeds the single-phase capacity, when three-phase equipment is being installed (large air conditioning, industrial motors, rapid EV chargers above 7 kW), or when expansion is planned that will exceed single-phase limits.
How do I know if I have a single-phase or three-phase supply?
Look at the meter and the cut-out at the supply intake. A single-phase supply has one live conductor entering the meter. A three-phase supply has three. The supplier can also confirm based on the MPAN profile class.
Is a single-phase supply cheaper than three-phase?
Yes on standing charge and meter operation fees. The unit rate per kWh is generally the same. New connections and upgrades cost less for single-phase than for three-phase.
Can a single-phase supply run three-phase equipment?
No. Three-phase equipment requires three live conductors offset by 120 degrees. A single-phase supply cannot provide this. The site would need to upgrade to three-phase or use single-phase equipment instead.
What voltage is a UK single-phase supply?
230 V nominal, with a permitted range of +10/-6 per cent under BS EN 50160. The actual voltage can vary from around 216 V to 253 V at any given moment.
Can I run a small EV charger on single-phase?
Yes for chargers up to 7 kW (32 A). Larger chargers (22 kW and above) require three-phase. A 7 kW charger fits comfortably within a 100 A single-phase supply if no other significant loads are running at the same time.