Is my electricity supply suitable for your heaters?

This page applies to the UK only. The electricity supplies in other countries may be different. Consult a local electrical engineer for details.

Once you have performed a heatloss calculation and worked out what size heaters you require, you need to check if your electricity supply is suitable. In the specification table for each heater you will find their voltage, phase, current and frequency requirements.

Before you order a heater you should verify that the electricity supply in your building is suitable for the electric heater(s) you intend to buy.

You need to consider:-

Supply Frequency

The standard electricity supply frequency in the United Kingdom is 50Hz, all of our heaters are designed to work on this. Unless you have a very specialised (rare!) electricity supply you shouldn’t need to worry about this.

Supply voltage & phase

Most of our heaters are designed to work on 400v 3 phase supplies, although we do stock some 230v and 110v single phase models. Heaters designed to work on one voltage will not work on another!

110 volt single phase – used for portable equipment on building sites and in commercial buildings. 110v supplies normally have BS EN 60309 yellow round sockets.

230volt single phase – also referred to as 240v. This is the most common voltage. Small portable heaters up to 3kw are fitted with the standard (BS1363) 13Amp 3 pin plugs as found in homes, offices, shops, etc. Portable heaters over 3kw are fitted with blue circular industrial plugs (BS EN60309).

Fixed heaters are permanently connected by an electrician.

400volt 3 phase – also referred to as 415v. Installed in industrial and commercial buildings to supply large electrical equipment. Portable heaters plug into round red industrial sockets.

Fixed equipment is permanently wired in by an electrician. 400v 3 phase wiring can be identified by its colour. Prior to April 1st 2004 it was red, yellow, and blue, with a black neutral. After this date for European harmonisation it became brown, black, and grey, with a blue neutral.

If a building does not have a 3 phase supply installing it can be expensive. For details contact your electricity supplier.

Available supply current

Possibly the most confusing aspect of choosing a heater, and the thing which catches most people out!

All electrical appliances (heaters, lights, computers, kettles) draw current, the bigger the appliance (kw), the more current (a) it will draw:

Current (A) = Power (kW) / Voltage (V)

The maximum current into a building is limited by the size of the incoming supply cable, which is protected by the supply fuse. The difference between the rating of the supply cable and fuse and the total current requirement of every electrical appliance in the building is called the ‘spare current capacity’

Spare current capacity (Amps) = Supply fuse rating (Amps) – total current requirement of all appliances (Amps)

Assuming electrical heaters are being added to an existing building. It is important that they do not draw more spare current than is available otherwise the supply fuse will blow. Upgrading the supply cable and fuse although expensive is a possibility, for details contact your electricity supplier.

Even if you have enough spare current capacity there are other things to consider:

13A 230V sockets are often wired on a ‘ring’. This means that although there may be any number of sockets in a building, the total current draw of a ring is limited by a 32amp fuse or circuit breaker. Or put another way a maximum of two 3kw heaters.

Very important, you cannot plug an unlimited number of electric heaters into your 13A sockets!

Industrial BS EN60309 sockets. These are circular industrial red or blue sockets rated at 16, 32 or 63A. 16A sockets may be wired on a ring as above, but 32 and 63A sockets are normally wired direct and so should all be able to supply their full current rating simultaneously.

It is important the colour, size of the socket, and number of pins of BS EN60309 sockets match the plug on the heater; the heater specification tables give full details.

Working out whether your electrical installation can supply enough current for an electrical heater is very complex. For anything larger than a single 3kw heater, we advise all customers to speak to their electrician before ordering.

Conclusion

In the UK we use 3 different voltages, for the non technical user making sure their electricity supply is suitable for electric heaters is a daunting task. They need to make sure they have the right voltage, phase, enough spare capacity (current) and for portable equipment the correct sockets.

Purchasing an electric heater only to find your electricity supply is not able to run it, or requires upgrading is a frustrating and potentially expensive mistake.

We strongly urge all customers to confirm with their electrician that they have a suitable electricity supply before ordering an electrical heater. Given the voltage, phase, current consumption, and plug type (for portable equipment) of the heater(s) you intend to purchase, they will be able to determine whether or not your electricity supply is suitable.

Further reading:

• What size space heater do I need?
• How warm are electric heaters?