Safety notice

The calculators give the numbers the code tables give. They do not inspect your house, and electricity does not forgive mistakes.

• Follow your local code. The NEC is adopted with local amendments, sometimes an older or newer edition. Your inspector's interpretation is the one that counts.
• Get a permit. New circuits, generator inlets, transfer switches, EV chargers and batteries need one almost everywhere in the US. Some jurisdictions only allow licensed electricians to do the work.
• Follow the manufacturer's instructions. A nameplate's minimum circuit ampacity, maximum breaker size or required wire overrides any general calculation (NEC 110.3(B)).
• De-energize and verify. Turn off the breaker and test for voltage before touching any conductor. The service conductors in a panel stay live with the main breaker off.
• Never backfeed. Connect a generator to house wiring only through a listed interlock or transfer switch.
• Carbon monoxide. Generators outdoors only, at least 20 ft from the house, exhaust pointed away. Details.
• When in doubt, hire a licensed electrician.

Wire & Watts provides these calculators for information only and accepts no liability for work carried out using them. See the terms.