Three-phase supply delivers 415V line-to-line (230V line-to-neutral) versus the standard 230V single phase. It matters in London because household loads are stacking up — two EV chargers on the drive, an air-source heat pump, an induction kitchen and (increasingly) home-office HVAC will push a typical 100A single-phase service into trip territory. Three-phase splits the load across three 100A legs, gives access to industrial appliances and future-proofs the property for the 2030s grid mix.
DNO (Distribution Network Operator) liaison is the slow bit. Most of London sits under UKPN; pockets of west London sit under SSEN. New generation (solar export, V2G) goes via G98 (single inverter ≤16A per phase) or G99 (anything larger or three-phase). A realistic single-to-three-phase upgrade is 4-12 weeks from DNO application to energisation, and £3,000-£8,000 total depending on dig length, cable upgrade and metering arrangement. Where the budget or timing doesn't fit, a load-balancing single-phase EV charger is often a workable interim. Electrician London (NICEIC Reg 619783000) handles every stage.
Why Electrician London
DNO application + G99 paperwork
UKPN or SSEN application drafted, submitted and chased. G99 / G98 generation paperwork where solar, battery or V2G is in scope.
TP&N distribution board upgrade
New three-phase TP&N consumer unit or distribution board, sub-mains, balanced phase allocation and Type A RCBO compliance throughout.
Load assessment + future-proofing
Diversified-load calculation per BS 7671 across EV, heat pump, induction and commercial loads. Sized for the next 15 years, not just today.
NICEIC commissioning
Reg 619783000. Every three-phase install signed off under our NICEIC scheme — commissioning certificate and full test sheets.
Three-phase supply pricing
Indicative. Final cost depends on dig length, cable size, DNO contractor charges and metering arrangement.
Photo + load assessment (refunded against quote)
Site visit, load calc, DNO viability check
£75
Three-phase distribution board only (existing supply)
Where three-phase already at meter — new TP&N board
From £1,495
Single to three-phase DNO upgrade + new board
Full DNO application, dig, cable, new metering, TP&N board
From £4,995
Commercial three-phase distribution + metering
TP&N board, sub-mains, MID metering
From £3,995
Load-balancing single-phase EV alternative
Where three-phase is not viable — dynamic load balancing instead
From £895
What's covered in a three-phase upgrade
- Diversified-load assessment to BS 7671
- DNO G99 / G98 application drafted and submitted
- UKPN or SSEN liaison through to energisation
- Dig, ducting and cable upgrade (via DNO contractor)
- New TP&N consumer unit or distribution board
- Three-phase sub-mains and balanced phase allocation
- New three-phase metering arrangement
- Commissioning to BS 7671:2018 + A4:2026
- NICEIC certificate and full test sheets
- Building Control sign-off where structurally required
Frequently asked questions
Do I actually need three-phase?
Most London homes do not — a single 100A phase covers most usage. You need three-phase when stacking high loads simultaneously: two 7kW EV chargers (14kW), heat pump (3-7kW), induction range (7kW) and instant water heating will exceed a single 100A service. A load-balancing single-phase EV charger is often a cheaper alternative — we model both at survey.
UKPN or SSEN — which DNO covers me?
Almost all of Greater London sits under UK Power Networks (UKPN). The exception is pockets of west London (parts of Hounslow, Hillingdon, Ealing toward the Thames Valley) which fall under SSEN (Scottish and Southern Electricity Networks). We check your DNO by MPAN at the survey before any application is drafted.
G99 vs G98 — what is the difference?
G98 covers Type A generation — a single inverter rated ≤16A per phase (≈3.68kW single-phase, ≈11kW three-phase). Anything larger, or any three-phase generation, requires a G99 application (with formal acceptance before energisation). For most domestic solar + battery installs the threshold matters; we file the correct form on day one.
How long does the whole upgrade take?
Realistic timeline: 1-2 weeks from application to DNO quote, 4-8 weeks from acceptance to dig and connection, 1-2 weeks for the meter operator to swap in the three-phase smart meter. Total 6-12 weeks. We push DNOs hard but cannot control their queues.
What drives the cost?
Three big variables. (1) Dig length — kerb to property; if your supply enters at the back of the house, it costs more. (2) Cable size — load assessment determines 25/35/95mm sub-main. (3) Metering — replacing a single-phase smart meter with a three-phase smart meter involves the meter operator separately. We itemise all three on the quote.
Can't I just load-balance the EV charger instead?
Often yes. Modern OCPP chargers (Zappi, Andersen, EO, Wallbox) can dynamically throttle output based on house load, keeping you under the 100A main fuse. For one EV charger plus normal household load this is usually enough and avoids the DNO process entirely. For two EV chargers + heat pump + induction, you really do need three-phase.
What about heat pump + EV combined loads?
A 7kW heat pump pulling 30A simultaneously with a 7kW EV charger pulling 30A leaves only 40A for the rest of the house from a single 100A phase. That works until the kettle and induction hob come on. Three-phase splits this naturally — heat pump on one phase, EV on another, kitchen on the third — with each load only seeing its own phase headroom.
Do you handle commercial three-phase too?
Yes — small-shop, office, restaurant and light-industrial three-phase installs are routine. We commission TP&N boards, MID-compliant sub-metering, three-phase RCBOs and three-phase motor loads with cause-and-effect to building control where required.
Related services
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