Power cut guide
Home Generators for Power Cuts: Safety and Sizing
Quick answer: Size a generator by adding the running watts of everything you want to power at once, then allowing for the extra starting watts that motors such as fridges and pumps need for a moment when they switch on. Only ever run it outdoors, well away from doors, windows and vents, because its exhaust contains carbon monoxide, which can kill. Plug appliances into the generator directly with suitable leads, and never connect it to your house wiring unless a qualified electrician has fitted a proper changeover switch.
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A generator can keep a fridge, freezer, lights and phones going through a long power cut, which is why they are popular in rural areas that lose power in winter storms. Used carelessly, they can also be deadly. This guide covers both halves: how to pick the right size, and how to use and store one without putting your household or the engineers fixing the network at risk.
Do you need a generator at all?
For many households, a well-stocked kit and a battery power station are enough. Power stations are silent, need no fuel, and are safe indoors. Our guide to choosing a portable power station for power cuts explains what they can run.
A generator makes more sense if you:
- regularly lose power for many hours or days, for example on a rural overhead line;
- need to run larger loads, such as a freezer full of food, a well pump or a sump pump;
- have somewhere safe outdoors to run it, and somewhere safe to store fuel.
Whatever you decide, a generator does not replace the basics in our power cut emergency kit, such as torches, water and warm layers.
Running watts vs starting watts
Every electrical appliance has a running wattage: the power it uses once it is going. Some also need a short burst of extra power to get started. This is the starting (or surge) wattage.
- Resistive loads, such as kettles, toasters, heaters and filament bulbs, draw about the same power when they start as when they run.
- Motor loads, such as fridges, freezers, pumps, washing machines and power tools, can need several times their running watts for a second or two when the motor kicks in.
- Electronics, such as laptops, routers, TVs and phone chargers, use little power but are sensitive to rough or unstable supply.
A generator must cover the total running watts of everything switched on together, plus the biggest single starting surge. Many generator spec sheets list both a “rated” or “continuous” output and a “maximum” or “peak” output. Size against the rated figure, not the peak.
Sizing a generator: a worked example
Say your area loses power during a winter storm and you want to keep the following running. The figures below are illustrative, so check the rating plates on your own appliances or ask the manufacturer for starting figures.
| Appliance | Running watts (example) | Extra starting watts (example) |
|---|---|---|
| Fridge-freezer | 150 W | 600 W |
| Chest freezer | 100 W | 400 W |
| Four LED lamps | 40 W | 0 |
| Router and phone chargers | 40 W | 0 |
| TV | 100 W | 0 |
| Total running | 430 W |
- Add the running watts: 150 + 100 + 40 + 40 + 100 = 430 W.
- Find the biggest single extra starting load: the fridge-freezer at 600 W.
- Add them: 430 + 600 = 1,030 W at the worst moment.
- Add headroom so the generator is not working flat out. Allowing about a quarter extra gives roughly 1,300 W.
So in this example a generator with a rated (continuous) output of around 1,300 to 1,500 W would be a reasonable fit. If you add a kettle at 2,000 W or more, the total jumps sharply. In practice it is easier to avoid using high-wattage heating appliances on a small generator at all.
Our generator size calculator lets you pick appliances from a list and does the sums for you, including starting loads.
Tip: Stagger start-ups. Switch on the fridge, wait a minute, then the freezer. Two motors starting at the same moment can overload a generator that would cope with them one at a time.
Inverter vs conventional generators
| Inverter generator | Conventional (open-frame) generator | |
|---|---|---|
| Power quality | Clean, stable output suitable for laptops, TVs and chargers | Output can vary more; check suitability for electronics |
| Noise | Usually quieter, engine speed adjusts to load | Usually louder, engine runs at fixed speed |
| Fuel use | Generally more economical at light loads | Uses similar fuel whatever the load |
| Size range | Mostly smaller outputs, portable | Wider range, including larger outputs |
| Best for | Electronics, lights, fridge, shorter outages | Bigger loads such as pumps or tools |
For most households wanting to keep a fridge, lights and devices going, an inverter generator is the more practical choice. Whatever type you look at, read the manufacturer’s guidance on which appliances it is suitable for.
Running a generator safely
Outdoors only
Petrol and diesel engines produce carbon monoxide (CO), a gas you cannot see or smell. National Grid Electricity Distribution’s power cut advice is clear: never use a portable generator or barbecue indoors during a power cut. Indoors includes garages, sheds, porches, conservatories and cellars, even with the door open.
- Run it in the open air, well away from the house.
- Point the exhaust away from your home and your neighbours’ homes.
- Keep it away from doors, windows, air bricks and vents, so fumes cannot drift in.
- Follow any minimum distance in the manufacturer’s instructions.
- Keep children and pets away from it, and do not touch the hot exhaust.
Safety: Signs of carbon monoxide poisoning include headache, dizziness, feeling or being sick, tiredness, confusion and shortness of breath. If you suspect it, get everyone into fresh air straight away. Call 999 if anyone has trouble breathing, sudden confusion or loses consciousness. Fit a battery-powered carbon monoxide alarm, as mains alarms without a battery will not work in a power cut.
Weather and electricity
Generators produce mains-voltage electricity, so water is a real danger. Do not run one in rain or snow unless the manufacturer says it is designed for it or provides a cover for that purpose. Make sure your hands are dry, and keep it on a firm, level surface.
Leads and connections
- Plug appliances directly into the generator, or use a heavy-duty outdoor extension lead rated for the load.
- Fully unwind cable reels so they do not overheat.
- Never run leads through a window that is then closed on them, or under doors where they can be crushed.
- Check leads for damage before every use.
Refuelling
Switch the generator off and let it cool before refuelling. Spilt petrol on a hot engine can catch fire. Refuel outdoors, away from the house, and never while smoking or near a flame.
Storing petrol and fuel at home
A long power cut means keeping fuel on hand, and petrol is highly flammable. The Health and Safety Executive’s rules for storing petrol at home are:
| Amount of petrol | What you must do |
|---|---|
| Up to 30 litres | No need to tell anyone, but it must be in suitable containers (see below) |
| 30 to 275 litres | Notify your local Petroleum Enforcement Authority in writing with your name and address |
| Over 275 litres | You need a petroleum storage licence |
Suitable containers are plastic containers of up to 10 litres each, metal containers of up to 20 litres each, or a demountable fuel tank of up to 30 litres. Your local Petroleum Enforcement Authority is usually the fire and rescue service or trading standards.
- Never store petrol inside your home or any living space.
- Keep it in a well-ventilated garage or shed, ideally away from the house, away from heat and anything that could spark.
- Label containers “Petrol” and “Highly flammable”, and check them regularly for leaks or damage.
- Do not fill containers or pour petrol in the place where you store it.
- Petrol in your car’s tank does not count towards the 30 litres.
Diesel and LPG have different rules. If you plan to use either, ask your local fire and rescue service for advice before you stock up. Petrol also goes stale over time, so follow the generator maker’s advice on fuel and storage.
Connecting a generator to your house
Some people want a generator to power their home’s circuits directly, so the boiler, lights and sockets all work. This is possible, but only if a qualified electrician installs a changeover switch (also called a transfer switch). The switch physically disconnects your home from the electricity network before the generator is connected.
Safety: Never plug a generator into a household socket using a “suicide lead” or any homemade cable, and never wire one into your fuse box yourself. This back-feeds electricity into the network. It can kill engineers working on lines they believe are dead, and it can electrocute you or start a fire when the mains power returns.
When you have a changeover switch fitted, ask the electrician whether your network operator needs to be told. SSEN, for example, asks customers who hire a generator to let it know so it can make sure the setup is safe, and notes that only a qualified electrician can connect one safely. You can find your operator’s contact details on our network operators page.
Rooftop solar panels raise a similar issue: an ordinary system switches off in a power cut precisely so it cannot back-feed. Our guide to solar panels and home batteries in a power cut explains how backup-capable systems handle this.
Looking after a generator between power cuts
- Run it every few months, outdoors, so you know it starts and you remember how it works.
- Follow the maker’s servicing schedule, including oil checks.
- Keep the instructions, spare spark plug and a funnel with it.
- Store it somewhere dry and secure. A generator left outside can be a target for theft.
- Check your fuel stock for age and leaks at the same time as your emergency kit.
For the wider safety picture, including candles and gas appliances, read power cut safety: candles, generators and carbon monoxide.
Frequently asked questions
What size generator do I need to run a fridge-freezer in a power cut?
Check the fridge-freezer’s running watts and allow for its starting surge, which can be several times higher. Many small inverter generators can handle one fridge-freezer plus lights and chargers, but always compare your appliance’s figures with the generator’s rated output.
Can I run a generator in my garage with the door open?
No. Carbon monoxide can build up in a garage and seep into the house even with the door open. Run generators outdoors only, well away from doors, windows and vents.
Can I plug my generator into a wall socket to power the house?
No. This is dangerous and can kill. The only safe way to power home circuits is through a changeover switch fitted by a qualified electrician.
How much petrol can I keep at home for a generator?
Up to 30 litres without telling anyone, in plastic containers of up to 10 litres or metal containers of up to 20 litres, stored outside your living space. Over that, you must notify your local Petroleum Enforcement Authority, and over 275 litres you need a licence.
Will my network operator lend me a generator?
Generally, no, although in some long power cuts operators provide support for customers on the Priority Services Register. Ask your operator by calling 105.
Your next step: list what you would actually want running, use the generator size calculator to see what output you need, and decide where outdoors it could run safely before you buy anything. Keep 105 and the other numbers on our emergency numbers page to hand.
Sources
- HSE u2013 If you store petrol at home, or at a club/association or similar premises
- Greater Manchester Fire and Rescue Service u2013 Domestic and non-workplace petrol storage
- NHS u2013 Carbon monoxide poisoning
- National Grid Electricity Distribution u2013 Power cut safety first
- SSEN u2013 Your planned power cut explained
Checked against these sources on 28 October 2026. Rules and amounts can change – your network operator or Ofgem has the final word. Spotted something out of date? Tell us.
More on being prepared: Power Cut Emergency Kit: What to Keep at Home · All power cut guides