What is the difference between single-phase and three-phase electricity?

The majority of homes in the UK have a single-phase electricity supply. This means the maximum charging rate for electric cars is 7kW.

As pointed out by UK Power Networks, a single-phase supply is smaller than a three-phase supply. As the names suggest, the former has one wire, while the latter uses three wires.

In reality, much of the UK is served by a three-phase network, it’s just that most domestic properties use a single-phase connection. 

You tend to find three-phase supplies in commercial properties, where it’s possible to fit a faster charger, such as a 22kW unit.

How to check your electricity supply

Can I charge an electric car with a domestic plug socket

According to UK Power Networks, the best way to tell if a property has a three-phase supply is by looking at the electrical fuse. A single-phase supply will have one fuse, while a three-phase electricity supply will have three 100 amp fuses.

Here’s an overview of the typical domestic installations:

  • Three-pin plug: 2.3kW (slow)
  • Home charge unit: 3.6kW (slow)
  • Home charge unit: 7.4kW (fast)
  • Home charge unit: up to 22kW (fast)

All except the 22kW charge unit can utilise a single-phase supply.

Is a three-phase supply necessary?

Charging a smartphone

Homeowners tend to upgrade their electricity supply when they convert a house into flats, extend a property, or install high-power equipment such as an air source heat pump. The property will receive up to 70kVA of power.

In theory, a three-phase electricity supply should deliver faster charging times. However, much depends on the electric car in question. Many cars are unable to accept a 22kW home charge, so check your handbook or speak to the manufacturer before upgrading your property.

You also need to factor in the cost. This will vary, but you’ll be looking at something between £3,000 and £20,000. It’s for this reason that many electric car owners choose to install a 7.4kW home charging unit, which costs between £500 and £750 after the government grant.

Danny Morgan of Smart Home Charge argues that three-phase is overkill for the majority of electric car drivers. His smartphone analogy is valid: “Imagine charging your smartphone with a more powerful charger overnight while you’re asleep. It may well charge in one hour instead of two, but in both scenarios your phone will be fully charged when you wake up at 7am. You won’t have noticed the time saving.”

Morgan does concede that a three-phase supply makes sense if you’re charging a number of electric cars, but that’s likely to be a rare situation.

Our advice would be to opt for a 3.6kW or 7.4kW home charger, then take advantage of rapid charging when on the move.

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