Extension cords work fine for a fridge and a couple of lamps. But the furnace, the well pump, the sump pump and the ceiling lights are hardwired, and to run them from backup power you need a safe connection to your electrical panel. That’s the job of a transfer switch.
Why you can’t just plug into an outlet
Some people use a double-male “suicide cord” to backfeed the house through a dryer outlet. Please don’t. It can send power back down the utility lines and electrocute the line workers fixing them. It can overload your wiring and start a fire. And it can wreck your generator the moment grid power comes back.
It’s illegal almost everywhere, and for good reason.
How a transfer switch works
It makes sure the house is connected to either the grid or your backup source, never both at once. Your generator or power station plugs into an inlet box on the outside wall, you flip the switch, and the circuits you’ve chosen run from backup power.
Your options
| Option | How it works | Typical installed cost* |
|---|---|---|
| Manual transfer switch (6–10 circuits) | A subpanel next to the main panel, with a switch for each circuit. | $500–$1,500 |
| Interlock kit | A mechanical plate on the main panel. A backfed generator breaker can power any circuit, but only while the main breaker is off. | $300–$1,000 |
| Automatic transfer switch (ATS) | Switches over by itself when the grid fails. Standard with standby generators. | $1,000–$3,000+ |
| Smart home panel (battery brands) | A panel from the power station maker that works with their units, often automatically. | $1,000–$3,000+ |
*Costs vary a lot depending on where you live, the state of your panel and permit rules, so get local quotes.
Choosing your circuits
A manual transfer switch only covers a handful of circuits, usually 6–10. Common choices:
- Refrigerator
- Furnace blower or boiler
- Sump pump
- Well pump (a 240 V pump needs a 240 V source)
- Kitchen outlets
- A lighting circuit
- Internet and home office outlets
- Freezer
Then size your backup source for the circuits you’ll actually run together. The generator size calculator helps with that.
Power stations: 120 V or 240 V
Most portable power stations only put out 120 V. Through a transfer switch they can run 120 V circuits, but not a 240 V well pump, an electric dryer or most central AC. Some larger systems put out 120/240 V split phase and can feed the whole panel.
The inlet box and cord
Your backup source plugs into an outdoor-rated power inlet box with a matching cord. The usual sizes are 30 A (L14-30 or TT-30) and 50 A (14-50). Match the inlet to your generator or power station’s plug. And if it’s a fuel generator, keep it at least 20 feet from the house; that’s why inlet cords come long.
Do you need one?
If anything hardwired is part of your outage plan, especially the furnace or a well pump, get a licensed electrician to install a transfer switch or an interlock. It’s the safe, legal way to connect backup power to your home, and the first long outage usually makes it feel worth every penny.