The Complete Guide to Three-Phase Electricity

✔ A three-phase electricity supply is meant for buildings with high electricity use

✔ In the UK, the standard for most homes is single-phase electricity

✔ Switching from single-phase to three-phase electricity costs £3,000-£8,000

You might have heard the terms three-phase and single-phase electricity before, but never been quite sure what they mean.

In short, these terms designate two types of systems for delivering electricity from the national grid to a building, whether it’s commercial or residential.

In this article, we’ll explain what three-phase electricity is, how it’s different from single-phase, and what type of properties need it. We’ll also tell you how much it costs, and how to make the switch from single-phase to three-phase electricity, if you think you need to.

Single-phase vs three-phase electricity

Single-phase and three-phase electricity supplies are two systems for providing electricity to properties.

The main difference is three-phase electricity has a higher power capacity than single-phase electricity – so it delivers more electrical power at a faster rate.

The two systems also differ in terms of setup.

Single-phase electricity supplies typically require one fuse and one electric meter, and have two wires for supplying the electrical current.

Three-phase supplies, on the other hand, require three fuses. They have either one large meter, or multiple meters, and the electric current is supplied via three wires – hence the name.

Which ‘phase’ is more common?

Both single-phase and three-phase electricity systems are common.

Single-phase systems are generally used in domestic homes or small stores that have gas-powered heating – in other words, buildings with relatively low electricity usage.

Three-phase systems are commonly used in large buildings, such as business offices and industrial sites.

They can also be used in homes with high electricity consumption, such as large houses or farms, especially when these properties have several large electrical appliances.

Is it possible to have three-phase electricity in your property?

Yes, it’s possible to have three-phase electricity in your property. Most homeowners get it if they have homes with high electricity use.

This could be for one of several reasons. The size of the buildings is a big factor, but some people also switch to three-phase electricity when they install large electrical appliances such as a heat pump, a powerful electric vehicle (EV) home charger, or a stairlift.

The pros and cons of three-phase electricity

Advantages of a three-phase supply

The main benefit of a three-phase electricity supply is it has a higher power output than a single-phase supply, which is useful when you have several large electrical appliances.

A three-phase supply also has a more balanced power output than a single-phase system. Three wires distribute the electrical current more evenly than one, so the chances of having inconsistencies in voltage are much lower.

Lastly, three-phase electricity supplies are a little more efficient than single-phase ones.

That’s because having three wires conducting the electrical current reduces the risk of resistive loss – that is, when electricity is lost due to the resistance of a conductor, in this case the wires.

Disadvantages of a three-phase supply

The main downside of a three-phase supply is it’s expensive to install. The equipment itself costs more than the hardware needed for a single-phase supply, which means switching from single-phase to three-phase typically costs at least £3,000.

Installing a three-phase supply can also be complex – it’s not just a matter of switching out the fuse. It often involves digging up external wires that connect your property to the grid, and replacing them.

If these wires run under a public pavement, you’ll have to get permission from your local authority before beginning work. This also adds to the overall cost.

Do you need three-phase electricity for your home?

You might need three-phase electricity for your home if you plan on installing high-capacity electrical appliances, but it’s not always necessary.

We’ll go over whether you need three-phase electricity for three common home additions – solar panels, heat pumps, and EV chargers – in the following sections.

Solar panels

You don’t typically need to switch to three-phase electricity when you get solar panels.

Most residential solar panel systems come with a single-phase solar inverter that works seamlessly with your existing electricity supply.

However, if your home already has three-phase electricity, you need to make sure you get a solar system that has a three-phase solar inverter, so it’ll work with your existing electrical system.

Which electricity phase your property has also affects the maximum number of solar panels you can install without needing approval from your Distribution Network Operator (DNO).

For properties with single-phase electricity, the maximum peak power capacity for solar panel installations without gaining additional permission from your DNO is 3.68 kilowatt peak (kWp). For properties with three-phase electricity, the maximum is 11.04 kWp.

The average three-bedroom home only needs a system that’s 3.5 kWp, so this won’t be a problem for most homeowners. If you’re unsure of how many solar panels you need, head to our guide to find out.

If you’re thinking about getting a solar battery along with your panels, rest assured, this doesn’t mean that you need to switch to a three-phase supply.

Solar batteries store electricity that’s already passed through the inverter, so as long as you have the right inverter for your electricity supply, you won’t need to change anything else.

Heat pumps

You might need to switch to a three-phase electricity supply if the heat pump you install is larger than 14 kilowatts (kW).

A heat pump of that size or larger is typically only required in homes with over five bedrooms.

The average three-bedroom home only needs a 5 kW heat pump, so most homeowners in the UK don’t need to switch to three-phase electricity when they get one.

EV chargers

If you’re installing an EV home charge point that’s over 22 kW, you’ll need to switch to three-phase electricity.

Most people who choose to get a 22 kW home charger do so because of the fast charging time – it’ll fully charge the average EV in a little over three hours.

But 22 kW charge points are a luxury, not a necessity. Most people in the UK have a 7 kW charge point, which doesn’t require you to switch to three-phase electricity.

These models take a little longer to charge an EV – nine to 10 hours – but it saves you the hassle of having to switch from one electricity supply to another.

7 kW chargers are also cheaper than 22 kW ones – another reason why people opt for them. You can read more about EV charger installation costs on our page.

How to switch to three-phase electricity

To switch to three-phase electricity, you first need to contact your Distribution Network Operator (DNO) and request permission.

You can do this yourself, but it’s generally easier to have the electrician you hire to carry out the switch do it for you.

Once permission is granted by the DNO, the electrician will have to install new cabling, a new fuse, and a new metre box, as well as rewire the circuits in your home.

How much does it cost to switch to three-phase electricity?

Switching to three-phase electricity can cost anywhere from £3,000 to £8,000.

Factors that affect the cost include where the cables that connect your property to the grid are, and how far the nearest three-phase supply is from your home.

If your cables run under public paths, for example, the cost will be higher as you’ll need to get permits from your local authority.

How long does it take to switch to three-phase electricity?

Switching to three-phase electricity typically takes two to three weeks.

This includes the time it takes for your application to be reviewed and accepted, your property to be surveyed, and the work to be carried out.

The actual process of digging up the cables, replacing them, and installing new fuses and wires takes a few days.

Summary

Three-phase electricity can be a good option for big homes that use several large electrical appliances.

It could be a good idea to switch if, for example, you wanted to install both a heat pump and a powerful EV charge point.

In most cases, however, making the switch to three-phase electricity is more trouble than it’s worth. Unless you’re fully renovating a house, it probably isn’t worth it.

Three-phase electricity: FAQs