7kW vs 22kW EV Chargers: Do You Need a 3 Phase Supply?
Updated: Oct 9
The difference in one line: a 7kW charger runs on the single-phase supply almost every UK home has, while a 22kW charger needs a three-phase supply and a car that can accept 22kW on AC, and most homes and most cars have neither. So for the typical house, 7kW is the practical maximum, and a 3 phase EV charger only makes sense if you already have (or are prepared to pay for) a three-phase supply and drive a car that can use it.
7kW vs 22kW side by side
A 7kW charger:
runs on a single-phase supply at 32 A (230 V × 32 A is about 7.4kW)
suits nearly every UK house with off-street parking
charges a typical car overnight from low
works with every car that takes a Type 2 AC connection
A 22kW charger:
needs a three-phase supply, drawing 32 A on each of the three phases
only charges at 22kW if the car's on-board charger accepts 22kW on AC
on a single-phase supply, runs no faster than a 7kW unit
There is also a middle option. An 11kW charger uses three phases at 16 A each. Many cars that can't take 22kW on AC can take 11kW, so on a three-phase house 11kW is often the sensible choice.
Why most UK homes top out at 7kW
Because nearly all UK houses have a single-phase connection. Which? explains that although most of the UK network is three-phase, most homes are connected to only one of those three phases. One phase at 32 A gives you about 7.4kW, and that is the ceiling for a home charger on a normal supply. Which? puts the maximum for a typical UK home at 7.4kW for this reason.
Your supply also has to carry the rest of the house while the car charges. A 7kW charger is already a large load, which is why on every EV charger installation we work out the house's maximum demand before fitting anything. Where the supply is tight, a charger with load management can turn itself down when the house is busy, and the IET Code of Practice for EV charging installations covers how that load curtailment is allowed for.
Will your car even charge at 22kW?
Check this before anything else. The charger offers power, but the car's on-board charger decides how much it takes on AC. Which? notes that most cars have a maximum AC charging rate of 7kW to 11kW, and plug-in hybrids often less. The rapid charging figure in the brochure, often 100kW or more, is the DC rate at public chargers and has nothing to do with your home charger.
If your car's AC limit is 7kW or 11kW, a 22kW charger will charge it at 7kW or 11kW. You would pay for capacity the car can't use.
How much faster is 22kW in practice?
Less than the numbers suggest, because charging slows as the battery fills. The Energy Saving Trust gives these times for a 50kWh battery starting from 20%:
7.4kW: about 7 hours 45 minutes
11kW: about 5 hours 15 minutes
22kW: about 3 hours
For a car that sits on the drive overnight, 7kW already fills a typical battery before morning. The extra speed of three-phase charging matters most for households with two EVs, drivers who cover very high mileage, or cars that are only home for a few hours at a time.
How to tell if your home has a three-phase supply
Look at your supply position. A three-phase supply has three main fuses where the cable comes into the property, one for each phase, instead of the single fuse a normal house has, and usually a three-phase meter and board after it. If you're unsure, an electrician can confirm it in a few minutes, or your network operator can tell you. Don't open the network operator's sealed cut-out yourself.
If you do have three phases, a three-phase charger is a real option.
What does upgrading to three-phase involve?
A new three-phase supply is work for your local network operator (DNO), not your electrician, and has to be applied for. Which? notes that because the three-phase network is widespread, an upgrade from single phase is often possible, and suggests asking your energy supplier whether it is possible for you. The price and the timescale for the new supply are set by the network operator.
Inside the house, a three-phase supply usually means a new three-phase distribution board or consumer unit arrangement, which is notifiable work under Part P because it replaces the consumer unit, and the charger circuit is a new circuit. That makes the whole upgrade a substantial project. For a single car that charges overnight, it rarely pays for itself. It starts to make sense when you have several large loads to run at once, a fleet of cars on one drive, or a business premises.
Which should you choose?
Single-phase house, one car: 7kW. This is most homes.
Single-phase house, low mileage or a plug-in hybrid: 7kW, or a cheaper 3.6kW unit.
Three-phase house, car accepts 11kW: an 11kW charger.
Three-phase house, car accepts 22kW, and you need the speed: 22kW.
Single-phase house, wants 22kW: only with a supply upgrade, and only if the car can use it.
We fit chargers for homes and businesses, and on every survey we check the supply type, the main fuse and the consumer unit before recommending a power rating. Power is only one of the EV charger installation requirements; earthing, RCD type and the smart charging rules matter just as much.
The move to home charging is one of the biggest changes to how houses use power, alongside heat pumps and new wiring rules, as we cover in our look at UK home electrical trends. If you're not sure which phase you have or which charger suits it, we can check on a visit anywhere across Shropshire and the West Midlands.
3 phase EV charger questions, answered
Can a 22kW charger be fitted to a single-phase supply?
On a single-phase supply it can only ever deliver what one phase allows, about 7kW. You pay extra for the unit and get no faster charging.
Is 7kW enough for two electric cars?
Often, yes, if both cars are home overnight and you alternate or schedule charging. A charger with load management, or two chargers sharing the supply, can help. Your installer needs to check the supply can take it.
Does a three-phase charger need a bigger consumer unit?
It needs a board and protection designed for three-phase, which is not the same as a standard single-phase consumer unit. If your existing board is old or full, a consumer unit upgrade may be part of the job either way.
Comments