A portable generator can keep the fridge, lights, internet and furnace fan running in an outage. The safe way to connect it to your house is a generator inlet plus a transfer switch or a panel interlock.
Why is plugging a generator into a wall outlet dangerous?
A "double male" cord into a dryer or wall outlet backfeeds your house wiring with no protection. It can send power out onto the utility lines, which can kill a line worker or a neighbor, it can energize your house when the grid comes back, and the exposed prongs of the cord are live. Never do it.
How does an inlet and interlock work?
- A weatherproof inlet box on the outside wall, where the generator cord plugs in.
- A dedicated breaker in your panel fed from the inlet.
- A listed interlock kit on the panel that physically prevents the main breaker and the generator breaker from being on at the same time, so the generator can never feed the utility lines.
You then choose which circuits to run by turning breakers on and off, staying within the generator's rating. A manual or automatic transfer switch does the same job in a different way.
What size generator inlet do I need?
Match the inlet to the generator's largest outlet: 30-amp (often a 4-prong L14-30) or 50-amp (often a 14-50 or CS6365). Use the generator sizing estimate to see roughly what your loads add up to.
How much does a generator inlet and interlock cost?
IES installs a 30-amp to 50-amp portable generator inlet with interlock for $1,750 to $1,960, including the breaker.
About these prices: rough starting-at prices from the IES price book. The final price depends on what we find on site, your utility and your city or county. Estimates are free.
Generator safety reminders
- Run generators outdoors only, far from windows, doors and vents. Carbon monoxide kills, and you cannot smell it. Have working CO alarms inside.
- Use a cord rated for the generator's output.
- Turn the generator off and let it cool before refueling.
Common questions
Is a generator interlock legal in California?
A listed interlock kit approved for your specific panel, installed with a permit, is an accepted way to connect a portable generator. A homemade connection or a back-feeding cord is not.
Can I plug my generator into my dryer outlet?
No. Backfeeding through an outlet is dangerous to you, your neighbors and utility workers. Use a properly installed inlet with an interlock or transfer switch.
General information for California homes under the California Electrical Code (based on the NEC). Local rules and inspectors can vary. Not a substitute for an on-site inspection. Never work inside a panel, at the meter or on live circuits.