Standby Generators & Transfer Switches — NEC 702 Requirements
The one absolute rule for backup power is that a generator can never be connected to house wiring in a way that could backfeed the utility — that’s how line workers get killed. Everything else in NEC Article 702 flows from that: listed transfer equipment, correct sizing, and proper grounding. Here’s what a compliant optional standby installation looks like.
Worth knowing
- A “suicide cord” (male plug on both ends) into a dryer or range receptacle is illegal everywhere, defeats every safety layer in this article, and energizes utility lines — an interlock kit costs less than the fine.
- Run portable generators outdoors only, at least 20 feet from the house with the exhaust aimed away — CO from a generator in a garage or near an open window kills faster than most people expect. Newer portables with CO shutoff sensors are worth the premium.
- Permanently installed standby generators must also meet the manufacturer’s listed clearances to openings and property lines — commonly 18 inches from the wall and 5 feet from windows and doors, but the listing controls.
- Recent NEC editions require GFCI protection on portable generator receptacle outlets (125V, 15/20/30A), which can nuisance-trip with some transfer setups — check compatibility before buying.
- Optional standby systems fall under Article 702; if your generator serves life-safety loads (rare in homes), Articles 700/701 impose much stricter rules.
Common questions
What does the code say about transfer equipment required for Generator Transfer Switch?
Any generator connection to premises wiring requires transfer equipment that prevents simultaneous connection of the generator and the utility — a transfer switch or a listed mechanical interlock on the panel. (NEC 702.5)
What does the code say about sizing — manual transfer for Generator Transfer Switch?
With manual transfer equipment, the system only has to be sized for the loads you intend to run, and the user is responsible for load management — you can legally run a small generator into a whole-house interlock. (NEC 702.4(B)(1))
What does the code say about sizing — automatic transfer for Generator Transfer Switch?
An automatic transfer switch requires the generator to carry the full calculated load that transfers, or the system must include automatic load management (load-shedding controls). (NEC 702.4(B)(2))
Adopted edition by state
Base-code year from BuildSpec’s adoption records. States often amend the base code, and your city or county may differ, so confirm with your building department.