Home Backup Setups: Transfer Switches, Interlock Kits and What Is Safe to Plug In
There are four safe ways to power a home from a generator: extension cords to individual appliances, a manual transfer switch, an interlock kit, or an automatic transfer switch with a standby generator. Any method that connects to your home's wiring needs a licensed electrician. Never power your house by plugging a generator into a wall outlet.
Why you need a proper connection
If a generator feeds your home's wiring without disconnecting it from the utility, power can flow backward onto the grid. This is called backfeeding. It endangers line workers repairing the outage, and it can damage your generator and home wiring. Transfer switches and interlock kits prevent it by physically isolating your home from the grid before the generator connects.
Your options
| Method | How it works | Approximate installed cost | Trade-off |
|---|---|---|---|
| Extension cords | Plug appliances directly into the generator | Under $200 for cords | Simple, but cords run through windows or doors and you can power only a few items |
| Manual transfer switch | A small panel moves chosen circuits to generator power | $800 to $2,000 | Powers only the circuits you pick; you start the generator and flip the switch |
| Interlock kit | A sliding plate on your main panel prevents the main and generator breakers from being on together | $500 to $1,500 | Powers any circuit but you must manage the load by hand |
| Automatic transfer switch | Senses the outage and starts a standby generator | $8,000 to $20,000 or more with the generator | Hands-free but the most expensive |
Costs are rough and vary by region, panel and electrician.
What you need besides the switch
- A power inlet box mounted on the outside wall, where you plug in the generator cord
- A generator cord that matches the inlet, commonly a 30-amp or 50-amp 240 V connection
- A generator with a matching outlet. Check the outlet type before you buy
- A permit and inspection, where your area requires them
An interlock kit must be the model approved for your specific panel. Your electrician can also confirm how your generator's neutral and ground are set up, since this affects safety.
What is safe to plug in
- Appliances with motors, such as refrigerators and freezers, are fine if the generator's starting watts cover them
- Phones, laptops, TVs and other electronics are best on an inverter generator or a power station, which supply cleaner power
- Use a surge protector for sensitive electronics
- Skip high-draw items such as electric ovens, electric water heaters and central AC unless your generator is sized for them
Choosing between the options
- If you only need a fridge and a few lights for a day or two, extension cords are enough
- If you want to run furnace fans, sump pumps or well pumps, a transfer switch or interlock is worth the cost
- If you want power to return without you doing anything, look at standby
Our sizing guide helps you size the generator, and the safety guide covers cord and placement rules.
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