This is the most dangerous piece of kit in the plan
A generator is a petrol engine producing carbon monoxide at a rate designed to move a vehicle, running unattended, near a house full of sleeping people, in the exact conditions where everyone is cold and tired and improvising.
Estimates put US portable generator carbon monoxide deaths at roughly 70 to 100 a year. These are not people who did something outlandish. They are overwhelmingly people who ran a generator in a garage with the door open, or under a lean-to, or on a porch, and believed that was outdoors.
What carbon monoxide does to a body, how fast, and why an alarm is slower than you expect, is on ventilating indoor burning. Read that page first. This one is about the machine and where it goes. The medical side is on carbon monoxide poisoning.
Distance, and why the usual number is not enough
Aim the exhaust away from the building. Not across it, not along the wall, away from it.
Think about where the air goes, not just how far the machine is. A generator 8 metres away at the bottom of a slope, in still air, on a cold night, is upwind of your house in the only sense that matters, because cold air and its contents run downhill.
A CO alarm in every sleeping room whenever a generator is running. Battery powered, tested, and inside the house rather than near the machine. This is not optional, and it is the last line rather than the first.
The places people put them that kill
Every one of these has killed someone, and every one felt reasonable at the time.
- A garage with the door open. This is the single commonest fatal mistake. An open door does not make an enclosed space ventilated. CO accumulates in the volume regardless, and the attached garage shares air with the house.
- A carport, lean-to, porch or covered walkway. A roof over it makes it an enclosure.
- A shed or outbuilding, whatever the ventilation.
- A cellar or basement. Never, under any circumstances.
- In a doorway to keep it out of the rain, which is putting the exhaust directly into the building.
- Under an open window, including an upstairs one, and including one you are not thinking about because it is on the other side of the room.
- Next to an air brick, extract vent or trickle vent.
- Inside a tent or awning.
- In a van or caravan, including with the side door slid open.
The generalisation: if it has a roof, or three walls, or is within 6 metres of anything anyone breathes in, it is the wrong place. Rain is a solvable problem. Use a purpose-made open-sided generator cover, or build a shelter with genuinely open sides that is still 6 metres out.
Refuelling
- Refuel outside and away from the machine, not standing over it.
- Never store fuel near the generator while it runs, and never indoors. The law and the practicalities are on generator maintenance and fuel storage.
- No smoking, no naked flame, no torch that is not sealed.
- Wipe up spills before restarting, and give the vapour time to clear.
- Use a proper spout or funnel. Fumbling a heavy can in the dark is how spills happen.
Never backfeed the house
Without a transfer switch, run appliances directly from the generator on extension leads. This is not a compromise, it is simply the normal way to do it, and for most households it is entirely sufficient. Lights, a fridge, charging, a kettle in turns.
Rain, damp and earthing
- Generators and water do not mix, and the answer is never to bring it under cover. Use an open-sided purpose-made cover.
- Stand it on something dry and stable. A pallet, paving, or a board. Not on wet grass or bare soil.
- Dry hands, dry leads. Wet hands on a generator outlet is a genuine electrocution risk in a way that 12V is not.
- Earthing depends on the machine. Many portable generators are designed with the frame bonded and do not need a separate earth rod when appliances are plugged directly into them. Others do. Read the manual for your specific machine, because this varies and is one of the few generator questions where general advice is genuinely unreliable.
- Use an RCD between the generator and anything you plug into it if the machine does not have one built in.
Leads and loads
- Use heavy outdoor-rated extension leads, and note that they must be uncoiled. A coiled lead under load overheats, because the coil is an inductor and a heat trap. This melts leads regularly.
- Add up what you are plugging in. The running watts figure, not the starting watts figure, is the one that governs continuous use.
- Anything with a motor needs a surge on startup, often two to three times its running figure. A fridge that runs on 150 W may want 500 W to start. Start large loads one at a time.
- Do not run it at full load continuously. Around 75% is a sensible ceiling for both fuel economy and engine life.
- Do not run it at almost no load for hours either. Light loading over long periods glazes bores and causes wet stacking in diesels, where unburnt fuel accumulates in the exhaust.
- Sensitive electronics want an inverter generator, not a cheap open-frame one. The waveform from a basic alternator is rough enough to damage some equipment over time.
Noise, and who now knows you have power
Worth thinking about before you need to.
A generator is audible for a considerable distance, especially at night when there is no traffic and no other machinery running anywhere. In a wide area power cut, yours may be the only sound for a mile, and it announces continuously that this house has fuel and working equipment.
This is a judgement, not a rule. Options are running it only in daylight, running it in short scheduled bursts to charge a battery bank rather than continuously, siting it behind the building, and building a baffle out of anything dense. Never enclose it to quiet it. That is the fatal mistake dressed as a sensible precaution.
The better long-term answer is that a generator charges a battery bank, and the battery bank runs the house. An hour of noise a day instead of eighteen, far less fuel, and no exhaust at night. See sizing a 12V system for the bank that makes that possible.
Before you start it, every time
- Oil level checked. Small engines are killed by low oil more than anything else, and many have a low oil cutout that stops the engine without telling you why.
- Fuel level checked, so you are not refuelling in the dark.
- Sited 6 metres out, exhaust pointed away, nothing above it.
- Nothing plugged in yet. Start it unloaded, let it settle, then add loads one at a time.
- CO alarms in the house are working. Test them with the button.
- Air filter clean, especially if it has been stored.
- Everyone in the house knows it is running.