Transfer Switch vs Interlock (vs Extension Cords)
Updated July 2026
Three legitimate ways to get generator power into a house: extension cords to the appliances ($50, zero wiring), an interlock kit feeding the whole panel ($400 to $900 with the electrician), or a dedicated transfer switch ($700 to $1,800 installed). The fourth way people try, a double-male cord into a dryer outlet, energizes the utility lines outside your house and can electrocute the lineman repairing them. That's the whole safety lecture; here's how to choose among the real three.
Extension cords: legitimate and underrated
For a fridge, a freezer, some lamps, and the phone chargers, cords are the intended design. Rules that keep it safe: 12 AWG minimum for anything with a motor, outdoor-rated, as short as practical, through a window or door gap that doesn't pinch, generator its full 20 feet from the house with exhaust pointed away. What cords can't reach is anything hardwired: the furnace, the well pump, the sump on a finished ceiling. The moment those matter, you're in the next paragraph.
Interlock: the whole panel for the price of a bracket
An interlock is a sliding steel plate on your panel plus a generator inlet on the wall. The plate physically prevents the main breaker and the generator backfeed breaker from being on together, so the house can't feed the street and the street can't feed the generator. Flip the main off, slide, flip the generator breaker on, and every circuit in the house is available; you choose what to run by flipping ordinary breakers, with the generator's rating as the budget. Parts run $50 to $200, the inlet and wire a bit more, and the electrician visit does it in a morning. The kit must be listed for your exact panel model, which is the only common snag.
Transfer switch: the curated version
A small sub-panel beside the main one, feeding six to ten chosen circuits: furnace, sump, fridge, kitchen plugs, a bedroom. A mechanical switch per circuit selects utility or generator, so there's no main breaker ceremony and no way to overload by enthusiasm; the only circuits available are ones you pre-chose to fit the generator. That discipline is the feature: it's the setup you install for the household member who is not going to do breaker math in a dark basement. It's also what automatic standby systems use, in whole-panel form with a motorized switch.
Choosing
Cords if nothing hardwired matters. Interlock if you want maximum flexibility per dollar and you're comfortable being the brains of the operation each outage. Transfer switch if the operation needs to run without you, or the local inspector prefers it (a few do; call first, permits apply to all panel work). Whichever you pick, the generator side is the same: a 240V-outlet portable, a heavy cord, and fuel discipline. And a CO alarm on every sleeping floor, because the connection hardware is never the thing that hurts people; the exhaust is.
Questions people ask
Why exactly is backfeeding through a dryer outlet dangerous?
The double-male cord energizes your panel with the main breaker still connected to the grid, so your generator feeds the neighborhood’s wires, stepped UP to thousands of volts by the same transformer that normally steps power down. A lineman working the "dead" line gets the full output. It also fries your generator the instant utility power returns. Interlocks exist to make this physically impossible; they cost less than the cord.
Do I need a permit for an interlock or transfer switch?
Almost everywhere, yes: it is panel work, and the interlock kit must be one listed for your panel model for the inspection to pass. A permitted install runs $400 to $900 for an interlock with inlet, $700 to $1,800 for a transfer switch. Unpermitted panel work surfaces at the worst possible times, like insurance claims and home sales.
How far from the house should the generator run?
20 feet, exhaust pointed away from doors, windows, and vents, per CDC and every manufacturer manual. Never in the garage, attached or not, door open or not. Portable generator CO kills roughly 70 people a year in the US; a $30 battery CO alarm on each sleeping floor is part of the generator budget, not an accessory.