Three phase and EV charging: what actually changes

The short answer

Three phase lets you fit a 22kW home charger instead of a 7.4kW one. Around 97 percent of UK homes are single phase, and for the large majority of those a three phase upgrade is not worth doing for car charging alone. A 7kW charger adds roughly 25 to 35 miles of range an hour, which over a seven hour overnight window is somewhere between 175 and 245 miles. Very few drivers need more than that by breakfast.

What three phase changes, and what it does not

• It changes the maximum charger output. A myenergi Zappi v2.1, for example, is a 7kW unit on single phase and a 22kW unit on three phase. Same product, different supply.
• It changes how much total load the house can carry. Three phase spreads demand across three conductors instead of one, which matters when a heat pump, an oven, a shower and a car charger all want power at once.
• It changes the solar picture too. Three phase raises the ceiling on how much generation you can connect without applying for permission first, covered in our single phase versus three phase solar guide.
• It does not change how fast your car charges unless the car itself can take more than 7.4kW on AC, and most cannot use the full 22kW.
• It does not change the cost per unit of electricity. That is set by your tariff, not your supply, and our tariffs guide covers the overnight rates that actually move the bill.

Why 22kW rarely means 22kW

Home charging is AC, and every EV has an onboard charger that converts it to DC for the battery. That onboard unit is the bottleneck. Most UK EVs accept 11kW or less on three phase AC, so a 22kW wallbox on a 22kW supply will still deliver 11kW to a car that only accepts 11kW. The extra capacity sits unused, having been paid for twice, once in the charger and once in the supply upgrade.

Charger output figures per the myenergi Zappi v2.1 datasheet. Vehicle AC limits, supply split, upgrade costs and load balancing costs per UK EV charging and DNO connection guidance, accessed August 2026.

What a three phase upgrade costs

Roughly £3,000 to £4,000 where a three phase main already runs close to the property and the work is a connection rather than a civils job. Where trenching, road works or network reinforcement are needed, it climbs to £7,000 to £15,000 and beyond. For comparison, a typical 7kW smart charger costs £800 to £1,200 installed, so the upgrade alone can cost three to fifteen times the charger it is meant to improve.

Load balancing usually replaces the upgrade

The real question is almost never how fast the car charges. It is whether the house can run a 32A charger without tripping the main fuse when the shower, the oven and the kettle are also on. Load balancing answers that for a fraction of the price. A CT clamp fitted around the incoming mains measures total household current in real time, and the charger throttles its own output to keep the whole property inside the supply limit. Dynamic systems respond in about 1.5 seconds and let the charger run at full speed whenever the house is quiet, which overnight is nearly always. Adding CT based load balancing typically costs £40 to £100, and units like the Zappi ship with the grid sensor in the box.

Your main fuse rating decides whether any of this is needed. On a 100A supply, a standard 7.4kW charger is usually approved automatically and free of charge within one to five working days, and the installation follows the connect and notify route where the network operator is told within 28 days rather than asked in advance. On an older 60A supply, load management can often make the same charger safe without touching the incoming supply at all. Looped supplies, where one service cable is shared between two neighbouring houses, are the common complication: they cut the available headroom and sometimes need unlooping work before a charger goes in. Our guide to what an EV charger installation involves covers that sequence in full, and what a DNO is explains who is making the decision.

When three phase genuinely earns its keep

• Several large loads arriving together. A heat pump, a large solar array and a car charger landing in the same year is a different calculation from a charger on its own.
• Two EVs on one property. Two 32A chargers on a single phase 100A supply will spend a lot of time throttling each other.
• A car that genuinely accepts 11kW or more on AC and a driver who regularly needs a large top up in a short window rather than overnight.
• A property already close to its supply limit with electric heating, a workshop, an annexe or a substantial hot tub load.
• Three phase already at the boundary. If the cable is there and the job is a connection rather than a dig, the numbers change completely.

The order to check it in

If a charger is arriving alongside solar, a battery or a heat pump, model the whole load together rather than one system at a time. Start with the EV charging guide, then the heat pump guide for the biggest single addition to a domestic supply. Every county page on this site carries a local calculator so you can model the numbers for your area before anyone visits, so start at your county page. Installations are carried out by an MCS-certified installation team for your area, who handle the network operator paperwork from start to finish.