A Generator, a Changeover Switch and a Clear Boundary: Winter Backup Power Done Properly

Winter power cuts are uncommon across most of the UK, but when they occur they expose a boundary that is easy to overlook: the point where a private generator meets the public supply. A portable generator can keep a fridge, a heating pump or a few lights running, yet the same machine can become a serious hazard if it is connected to the house in the wrong way. The difference between useful backup power and a dangerous backfeed is not a matter of luck. It is a matter of isolation, earthing and protection.

Why a socket is not an inlet

Plugging a generator into a normal 13 A socket using a lead with plugs at both ends is sometimes portrayed as a quick fix. It is not. Once the generator is running, the male pins of the plug that would normally sit in the socket can become live. Anyone handling that lead is exposed to mains voltage, and when the public supply returns, two sources of energy can meet in the same wiring with no controlled separation. The lead itself can overheat, and the risk extends beyond the property: backfeed can energise wiring that distribution network operators and their contractors expect to be dead.

Leads of this kind are sometimes called suicide leads for good reason. They should not be made, sold or used. A generator should never be connected to a domestic installation through a standard socket, and a householder should be cautious of any advice that treats this as an acceptable temporary measure.

The changeover principle

Safe connection starts with a changeover switch, also known as a transfer switch. Its purpose is simple: it allows the installation to be supplied either by the mains or by the generator, but never by both at once. A proper changeover switch is break-before-make and mechanically interlocked, so the two supplies cannot be connected simultaneously. The generator is then connected to a dedicated generator inlet, usually mounted on an external wall, rather than to a socket intended for appliances.

This is fixed electrical work, not a plug-in accessory. In England and Wales, such work is likely to be notifiable under Part P of the Building Regulations, and it should be designed, installed and certified by a competent electrician. The certificate and schedule of test results matter: they show that the inlet, changeover device, protective conductors and final circuits have been assessed as a system. Where a permanent standby generator is intended, the distribution network operator should also be consulted at the planning stage.

Earthing, neutral and RCD protection

Portable generators are not all constructed in the same way. Some have a floating neutral, some have a bonded neutral, and the correct earthing arrangement depends on the generator and on the installation it is intended to supply. A householder should not assume that the consumer unit's existing RCDs will provide the same protection when the supply source changes. A generator is a separately derived source, and its neutral-to-earth relationship must be assessed before it is connected to fixed wiring.

An electrician will check whether an earth electrode is required, whether neutral-earth bonding is appropriate, and whether the protective devices will operate correctly under fault conditions. RCDs and RCBOs are valuable, but they are not a universal answer to every generator arrangement. The current edition of BS 7671 provides the framework, and the installation should be verified and tested rather than assumed to be safe because the generator starts and the lights come on.

Load discipline and extension leads

A generator should supply the circuits it has been sized to carry, not the whole house by default. Essential loads such as lighting, a fridge, a boiler pump or a small heater may be appropriate; electric showers, cookers, immersion heaters and heat pumps can quickly exceed a portable unit's capacity. Starting currents for motors and compressors also need to be considered, because a generator that runs a fridge may still trip when a larger appliance starts.

Where extension leads are used, they should be heavy-duty, fully uncoiled and rated for the load. Daisy-chaining several leads increases resistance and the risk of overheating. Outdoor leads should be suitable for the environment, kept away from water and damage, and checked for cuts, crushed insulation or loose plugs before use. A plug-in RCD can add a layer of protection for temporary equipment, but it does not replace a properly designed generator connection.

Fuel, exhaust and carbon monoxide

Carbon monoxide is the quiet risk with any fuel-burning equipment. A generator must never be run indoors, in a garage, in a shed, in a conservatory or in a porch, even if doors and windows are open. Exhaust fumes should be directed away from windows, doors and ventilation openings. A carbon monoxide alarm to EN 50291 should be fitted and tested in accordance with the manufacturer's instructions, but an alarm is a warning device, not a substitute for correct siting.

Fuel should be stored in a suitable marked container, outdoors and away from ignition sources. Generators should be allowed to cool before refuelling, and smoking or naked flames should be kept well away. Spilt fuel and hot exhaust components are both fire risks, and a generator that has been running for hours should be checked for overheating, damaged leads and any sign of distress.

A pre-winter check

Before winter 2026, households that rely on a generator should arrange for a competent electrician to inspect the changeover arrangement, generator inlet, earthing and protective devices. Test the carbon monoxide alarm, inspect extension leads, and keep torches and a battery radio accessible. Label the generator inlet clearly so that no one mistakes it for an ordinary socket.

If a fixed changeover switch is not in place, battery-powered lighting and a properly manufactured standalone power station are safer interim options than an improvised connection to the house wiring. The aim is not simply to keep the lights on. It is to keep a clear boundary between the generator and the public supply, so that backup power remains useful, controlled and safe.