Transfer switch
A transfer switch is a device that connects a generator to a home’s circuits while physically disconnecting them from the utility line, so generator power can never backfeed the grid. It is the code-required way to power hardwired circuits from a generator.
Backfeeding — energizing house wiring without isolating the utility connection — can electrocute line workers and destroy the generator when power returns. Manual transfer switches let you pick which circuits the generator carries; automatic transfer switches (on standby systems) do the switching themselves.
A manual transfer switch for a portable generator typically serves 6–10 essential circuits and pairs with an inlet box outside. Installation is an electrician’s job and normally requires a permit.