Home generator installation: sizing, transfer switches and safety

Do you need one?

EIA says U.S. electricity customers averaged about 11 hours of interruptions in 2024, nearly twice the average of the previous decade, and about 80% of that came from major events such as storms (EIA). In Illinois, EIA’s 2025 data show customers averaged about 146 minutes of interruptions including major events (EIA). A generator is most worth it if you have a sump pump, need power for medical equipment or medicines, or work from home.

Portable vs. standby

• Portable generators run on fuel you store and must be set up outside every time. Plug appliances in with heavy-duty outdoor cords rated for the load (CPSC).
• Standby generators are permanently installed outside and connected to your home’s wiring. The Red Cross calls a permanently installed stationary generator the best option (Red Cross).

How to size a generator

The Red Cross suggests this approach (Red Cross):

• Add up the power needs of each appliance and device you want to run. Check the label on the back or side.
• Add the wattage of the lights you’ll use.
• Choose a generator that produces more than you need, since some appliances draw up to 3 times as much power when starting up.
• If your needs are complicated, ask an electrician to help.

Don’t overload a generator, and make sure extension cords are rated for more than the total wattage of what’s plugged in (OSHA, CPSC).

The transfer switch

OSHA says never to attach a generator to a building’s electrical system unless a qualified electrician installs it with a transfer switch (OSHA). The Red Cross says the switch should be installed according to the National Electrical Code and local codes (Red Cross).

Never backfeed by plugging a generator into a wall outlet. CPSC says this can electrocute utility workers and neighbors served by the same transformer (CPSC).

Running it safely

• Keep it dry, and leave 3 to 4 feet of clear space around and above it (Ready.gov, OSHA).
• Turn it off and let it cool before refueling, and store fuel in an approved can outside living areas (Red Cross).
• Use CO alarms that meet UL 2034 or a similar standard, and test them monthly (CPSC, CPSC).
• Start it at least once a month, and use a gasoline stabilizer if it will sit unused for a long time, so it’s ready when you need it (Missouri PSC).
• Plan ahead for medicines and power-dependent medical devices, and keep the fridge and freezer closed during an outage (Ready.gov).

Hiring an electrician

• In Chicago, electrical work regulated by the city’s Electrical Code must be done by a licensed electrical contractor (City of Chicago). Elsewhere, ask your village or city what permits and licenses it requires.
• A standby generator that runs on natural gas also needs a gas line. Ask whether the estimate includes it, and if you ever smell gas, leave and call your gas utility from outside (Nicor Gas).
• Get written estimates from more than one contractor. For home repair work over $1,000 in Illinois, get a written contract and the “Home Repair: Know Your Rights” pamphlet (Illinois Attorney General).
• Be wary of storm-chasing contractors who knock on your door after an outage (FTC).

Protecting your basement? See our sump pump guide, our storm damage guide, our electrical guide and our home repair hub.