Generator safety: carbon monoxide, backfeeding and transfer switches
A portable generator is one of the most useful things to own in an outage and one of the most dangerous to use carelessly. The Consumer Product Safety Commission says most generator incidents it hears about involve carbon monoxide from generators used indoors or in partly enclosed spaces. Here is what CPSC and OSHA say to do instead.
Carbon monoxide: the main danger
Generator exhaust contains carbon monoxide (CO), a poison you can’t see or smell. CPSC warns that in a confined space a generator can produce high levels of CO within minutes, and that the danger label on every portable generator made since 2007 says it plainly: using a generator indoors can kill you in minutes.
- Never indoors. Not in the house, garage, basement, crawlspace or shed — CPSC says this applies even with fans running or doors and windows open. CO can build up and linger for hours after the generator stops.
- Outside, at least 20 feet away. CPSC’s storm-season advice is to use a generator “OUTSIDE your house ONLY, at least 20 feet from your home.” Keep it away from doors, windows and vents that could let exhaust in, with the exhaust pointed away from buildings. Follow the distance in your generator’s manual. OSHA adds 3–4 ft of clear space on all sides and above it for ventilation.
- CO alarms inside. CPSC recommends battery-operated CO alarms, or plug-in alarms with battery backup, certified to UL 2034 (or IAS 6-96 / CSA 6.19.01), tested monthly.
- Feel sick, get out. If you feel dizzy, sick or weak while a generator is running, get to fresh air right away.
RVs and campers are a special case: exhaust drifting into a slide-out, an open window or a roof vent is how CO gets inside your home or RV. Point the generator’s exhaust away from your rig and the neighbors’, give it the same 20 feet where the site allows, and keep a working battery-powered CO alarm in the RV.
Backfeeding: never plug a generator into a wall outlet
Plugging a generator into a household outlet with a double-ended (“suicide”) cord to power the house wiring is called backfeeding. CPSC calls it extremely dangerous: it presents an electrocution risk to utility workers and neighbors served by the same transformer, and it bypasses some of the house’s built-in circuit protection. OSHA explains why: a generator attached to a building’s wiring without a proper transfer switch can energize wiring for great distances.
The right ways to connect
- Cords to appliances. Plug appliances straight into the generator using heavy-duty outdoor extension cords. CPSC: the cord’s rating must exceed the total wattage plugged into it, the full length must be free of cuts, and the plug must have all three prongs.
- A transfer switch. OSHA: never attach a generator directly to a structure’s electrical system unless a qualified electrician has installed it with a transfer switch. The switch disconnects the house from the grid before the generator feeds it.
- Interlock kits with an inlet box do the same job where local code allows them — installed by a licensed electrician.
Sizing the generator for what you’ll connect is on the generator size calculator; worked examples include what size generator to run a house and what size generator to run a refrigerator.
Shock and wet weather
CPSC notes that generators can shock or electrocute, especially in the wet. If you must run one in rain, protect it from moisture under an open, canopy-like structure on a dry surface where water can’t pool — without moving it indoors or near openings. Dry your hands before touching it. OSHA adds: use GFCI protection in wet or damp locations, keep the generator properly grounded per the manufacturer’s instructions, and don’t use electrical equipment that has been under water until it has been dried and checked.
Fuel and fire
- Refuel cold. CPSC: turn the generator off and let it cool before refueling — gasoline spilled on hot engine parts can ignite.
- Store fuel outside living areas, in properly labeled, non-glass safety containers, and not near a fuel-burning appliance such as a gas water heater in a garage.
- Don’t overload it. OSHA warns overloading can overheat the generator and create a fire hazard. Keep the running load within its rating — see how long a generator runs on 5 gallons of gas for planning fuel at a given load.
Batteries as a quieter alternative
For short outages and small loads, a battery and inverter avoid exhaust entirely. A power station can keep a fridge or CPAP going for hours — see how long a power station runs a refrigerator — and the home backup battery calculator sizes something bigger. Battery systems connected to house wiring still need a licensed electrician and a proper transfer method.
Quick checklist
- Generator outdoors, at least 20 feet from the house (CPSC), away from doors, windows and vents, exhaust pointed away.
- Battery CO alarms working inside.
- Appliances on outdoor-rated, three-prong cords — or a transfer switch installed by an electrician.
- Never plugged into a wall outlet.
- Refuel only when off and cool; fuel stored outside living areas.
Frequently asked questions
Is it safe to run a generator in the garage with the door open?
No. CPSC says never to use a generator inside homes, garages, crawlspaces or sheds, even with doors and windows open or fans running. Deadly CO can build up quickly and linger for hours.
What is backfeeding a generator?
Powering house wiring by plugging a generator into a wall outlet. CPSC calls it extremely dangerous: it can electrocute utility workers and neighbors on the same transformer and bypasses household circuit protection. Use a transfer switch installed by a qualified electrician.
Do I need a transfer switch for a portable generator?
Only if you want to power the house wiring. OSHA says never to connect a generator to a building’s electrical system without a transfer switch installed by a qualified electrician. Otherwise, run cords from the generator to individual appliances.
How far should a generator be from the house?
At least 20 feet, outside, according to CPSC — and away from doors, windows and vents, with the exhaust pointed away from the house. Follow a larger distance if your generator’s manual gives one. OSHA also calls for 3–4 ft of clear space around and above the unit.
Sources
- U.S. Consumer Product Safety Commission — Portable Generator Hazards (Safety Alert 5123, 2021) (opens in a new tab) — Never run a generator indoors or in a garage, even with doors open; place it outside far from doors, windows and vents; CO alarms; never “backfeed” by plugging into a wall outlet.
- U.S. Consumer Product Safety Commission — CPSC Warns Consumers in Path of Storms to Take Precautions When Using Portable Generators (July 24, 2020) (opens in a new tab) — “Use your generator OUTSIDE your house ONLY, at least 20 feet from your home”; make sure you have working CO alarms.
- OSHA Fact Sheet — Using Portable Generators Safely (opens in a new tab) — Never attach a generator to a building’s wiring unless a qualified electrician has installed a transfer switch; 3–4 ft of clear space around the unit.