Key takeaways
3×
The load
Power a three-phase meter can carry vs. single-phase
400V
Three-phase
Versus 230V on a UK single-phase supply
£1k+
Typical cost
DNO installation, before any internal wiring
4-8 weeks
Lead time
From DNO application to commissioning
What is a three-phase meter?
A three-phase meter is the electricity meter fitted on a property that takes its supply from three live conductors instead of one. Each conductor carries an alternating current that is offset by 120 electrical degrees from the others, so the combined load is delivered smoothly and continuously rather than in the 50 Hz pulses of single-phase.
The practical consequence: a UK single-phase supply tops out at roughly 23-24 kVA (100 A fuse × 230 V). A three-phase supply can carry roughly three times that through the same physical conductors, and feeds appliances that need 400 V between phases: pretty much every commercial motor, oven, chiller and rapid charger sold in Britain.
The shortcut rule
If your total connected load is under 22 kW and your biggest single appliance is under 7 kW, a single-phase supply will almost certainly do the job. Above either threshold, get a three-phase quote from your DNO before you commit to the building work.
Side by side
Single-phase vs three-phase at a glance
The two supplies use the same low-voltage 50 Hz grid, but everything past the cut-out fuse changes: cable count, fuse rating, available voltage, and the meter itself.
Six common cases
Who actually needs a three-phase meter?
Three-phase is not just for heavy industry any more. The growth of induction kitchens, server rooms and EV charging hubs has pushed it into mainstream commercial use, and now into a small but growing share of homes.
Factories & workshops
CNC machines, welders, compressors and pump motors above ~10 kW almost always need three-phase. A single-phase supply trips on inrush.
Data centres & offices
High-density server rooms, rooftop HVAC and lifts. Three-phase keeps the load balanced and the cabling thinner.
Hotels & restaurants
Commercial ovens, induction hobs, walk-in chillers and big air-conditioning units. Most kitchens above 30 covers run three-phase.
EV charging hubs
Any DC rapid charger and most 22 kW destination chargers require three-phase. Single-phase tops out at 7.4 kW per port.
Solar & battery homes
A three-phase home can export across all three phases, balancing the network and avoiding G98/G99 single-phase export caps.
Construction & farms
Mobile cranes, grain dryers, milking parlours and welding bays. Almost every agricultural building is on three-phase.
How it works
Five steps from quote to commissioning
A three-phase upgrade always involves three parties: the Distribution Network Operator who owns the cable, your energy supplier who fits the meter, and a registered electrician who wires the consumer unit. Skipping any of them creates a non-compliant install that no insurer will cover.
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1
Confirm you actually need it
Total the nameplate load of every appliance and add a 25% headroom. If the figure exceeds ~22 kW or you are installing a 22 kW+ EV charger, three-phase is justified.
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2
Contact your DNO
The Distribution Network Operator (NPG, UKPN, NGED, SP Energy Networks, SSEN, Electricity North West) owns the cable from the substation to your meter. Three-phase upgrades are quoted under the "ENA G81" connection process.
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3
Pay the connection charge
Typical range: £1,000 to £5,000 for a service upgrade on a small commercial unit. New connections requiring a trench across a road can exceed £10,000.
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4
Schedule the supplier visit
Once the DNO has run the cable to the meter position, your energy supplier (British Gas Business, E.ON Next Business, EDF, etc.) fits the three-phase meter and commissions the supply.
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5
Update the consumer unit
An electrician then installs a three-phase consumer unit (TP&N distribution board) and assigns each circuit to one of the three phases. Loads should be balanced within ±10%.
Benefits and drawbacks
Benefits
- Up to three times the maximum load on the same fuse rating, so you can run motors, ovens and rapid chargers a single-phase site would trip in seconds.
- Redundancy: if one phase fails (a snapped underground cable, a tripped sub-fuse), the other two keep working. A single-phase fault takes the whole building down.
- Thinner internal cabling per kilowatt of load, which lowers copper costs on large refits.
- Solar and battery friendly: G99-compliant inverters can export across three phases, raising the cap from 3.68 kW per phase to ~11 kW total.
Drawbacks
- Installation cost: at least £1,000 for the DNO connection, more if a trench is needed. The internal rewiring adds another £500-£2,000.
- Higher standing charges: most business tariffs charge a standing fee per phase. A three-phase site pays roughly three times the daily standing charge of a single-phase site.
- Load-balancing required: an electrician has to spread circuits across all three phases. An unbalanced site can trip on the busiest phase while the other two are half-empty.
- Smart-meter inventory is tighter: SMETS2 three-phase meters are stocked by every supplier but installation lead times can be longer than for single-phase swaps.
SMETS2 three-phase smart meters
Since 2020, every UK domestic and small-business supplier has been required to fit a SMETS2 smart meter at any new install or upgrade. The three-phase variant became widely available in 2022 and is now the default at most large-load installations.
The meter reports the three phases independently to the DCC, which means your supplier can spot a chronically overloaded phase and recommend rebalancing before the fuse pops. In-home display units show total kWh and live kW; the per-phase breakdown is exposed in your supplier's app.
30 min
Reading interval
Half-hourly data sent automatically, no manual reads
3 phases
Independent reporting
Each conductor monitored separately for balance
Free
Supplier upgrade
No charge to swap an analogue three-phase meter
Heavy-load business? Compare quotes built for three-phase sites.
Three-phase tariffs vary by supplier, time-of-use band and capacity charge. Selectra's free comparison shortlists the best B2B suppliers for your peak demand and fuse rating in under two minutes.
UK business energy suppliers
Compare tariffs and contracts from every active UK business electricity and gas supplier.
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Frequently asked questions
Three-phase meters: your questions answered
Open the meter cabinet and look at the cable entering the meter. A single-phase supply has one thick brown live wire alongside a blue neutral and a green/yellow earth. A three-phase supply has three lives (brown, black, grey) plus a neutral and an earth. The fuse holder is also bigger and usually shows three separate cylindrical service-cut-outs.
The unit rate is set by your supplier, not by the meter type. A three-phase business tariff is usually quoted at the same p/kWh as the equivalent single-phase tariff. Where you save is on capacity charges and standing charges per phase: a balanced three-phase load lets you stay under the fuse rating that triggers the next half-hourly settlement band, which is where the big bills come from on heavy sites.
Yes. The SMETS2 three-phase variant began rolling out in 2020 and is now stocked by every major UK supplier. It reports each phase separately to the Data Communications Company (DCC), so you can see in-app whether one phase is overloaded. Older businesses still on a SMETS1 or analogue three-phase meter should ask their supplier for a free SMETS2 swap.
You need three-phase if you want a 22 kW charger (the most common destination-charger spec), any rapid DC charger, or two or more 7.4 kW chargers running simultaneously without tripping. A single 7.4 kW home charger works fine on a normal single-phase supply.
The site owner. The DNO charges for the cable, trench and service head. The supplier usually fits the meter free of charge if you are taking out a new supply contract. The electrician's consumer-unit rewire and any internal cabling are charged separately.
Plan for four to eight weeks from DNO quote acceptance to commissioning, assuming no road excavation. If the DNO has to dig across a public footpath or road, lead times can stretch to three months because of council permits.