Single phase vs three phase
When you start looking at EV charger specs, you’ll run into the terms “single phase” and “three phase” almost immediately. It sounds more complicated than it is. Here’s what you actually need to know.
What’s the difference?
Your electricity supply comes into your home through live wires. A single phase supply has one live wire delivering power at 230 volts. A three phase supply has three live wires, each carrying 230 volts but offset from each other, giving an effective 400 volts between them.
Think of it like a motorway. Single phase is a single-lane road. Three phase is a three-lane motorway. More lanes means you can move more traffic (power) at the same time.
Which one do you have?
The vast majority of UK homes have a single phase supply. Three phase is more common in commercial properties, farms, large detached houses and some newer-build homes.
There are a few quick ways to check:
- Look at your meter: A single phase meter usually has one row of digits or a simple digital display. A three phase meter is physically larger and may show three separate readings or have multiple rows.
- Check your consumer unit (fuse box): A single phase supply feeds in through a single main switch. Three phase has a three-pole main switch or three separate incoming supplies.
- Count the cables: The main supply cable to a single phase property contains two cores (live and neutral). Three phase has four cores (three lives and one neutral).
- Ask your DNO: Your distribution network operator can confirm what supply you have. Find yours at energynetworks.org.
If you’re not sure after checking, an electrician can tell you in seconds during a site survey for your charger installation. Our home charging basics guide covers what to expect from the survey and installation process.
How it affects EV charging
This is the practical bit. Your electricity supply type determines the maximum charging speed you can install at home.
Single phase (7kW max): A 7kW charger draws about 32 amps from your supply. On a single phase connection, that’s the practical maximum for a dedicated EV charger. It adds roughly 25-30 miles of range per hour of charging.
Three phase (22kW max): With three phase power, you can install a 22kW charger that draws about 32 amps per phase. Three times the power, three times the charging speed. You’d add 75-90 miles of range per hour.
Worth noting: your EV also needs to accept three phase AC charging to benefit. Most EVs sold in the UK have single phase onboard chargers (limited to 7kW AC). Some European-spec models, particularly from Renault, VW and BMW, come with 11kW or 22kW onboard chargers. Check your car’s specifications before assuming a three phase charger will make a difference.
Do you actually need three phase?
For most people, the honest answer is no.
A 7kW charger plugged in overnight (say 11pm to 7am) adds around 200-240 miles of range. That’s more than enough for typical daily driving, especially on a cheap overnight tariff like Go or Intelligent Go. Even if you have a longer commute, you’d need to be driving well over 100 miles every single day before a 7kW charger couldn’t keep up.
Where three phase starts making sense:
- You’re charging multiple EVs: Two cars sharing a single phase supply can be a squeeze. Three phase lets you install two 7kW chargers (or one 22kW) without stressing the supply.
- You run a business from home: If you have high existing electrical demand from equipment, adding a 7kW charger might push you over your single phase capacity.
- You have very limited charging windows: Perhaps you can only charge for a few hours a day. Faster charging makes up for less time plugged in.
- Commercial premises: If you’re installing chargers at a workplace or commercial property, three phase is usually already available and the faster speeds make sense for vehicles that come and go during the day.
The cost of upgrading
If you want three phase and don’t currently have it, your DNO can upgrade your supply. It’s not a quick or cheap process.
Typical costs: £1,000 to £3,000, sometimes more depending on the distance from the nearest three phase infrastructure and how much civil work is needed (digging trenches, for example).
Timescales: Anywhere from 6 weeks to several months. Your DNO needs to survey the site, plan the work, possibly get wayleaves from neighbours if cables cross their land and schedule the installation.
The process: Contact your DNO and request a quotation for a three phase supply upgrade. They’ll survey your property and provide a fixed price. Once you accept and pay, they schedule the work.
For most EV owners, the cost and hassle of upgrading to three phase far outweighs the benefit. The money is almost always better spent on a good 7kW compatible smart charger and a cheap overnight tariff like Intelligent Go.
Quick comparison
| Single phase | Three phase | |
|---|---|---|
| Supply voltage | 230V | 400V |
| Max home charger | 7kW | 22kW |
| Range added per hour | ~25-30 miles | ~75-90 miles |
| Overnight charge (8hrs) | ~200-240 miles | ~600+ miles |
| UK homes | ~95% | ~5% |
| Upgrade cost | N/A | £1,000-3,000 |