Transfer switch vs interlock kit: how to connect backup power to your house
There are a few legal ways to run house circuits from a generator or power station. Each one keeps your backup power from flowing back onto utility lines.
Safety: This page explains your options. It is not wiring instructions. Any work in your electrical panel, including transfer switches, interlocks, and inlets, should be done by a licensed electrician with a permit where your town requires one.
What the rules say
NEC 702.5 requires listed interconnection or transfer equipment for optional standby systems. It must prevent the backup source and the utility supply from being connected at the same time (UpCodes, NEC 702.5, as of 2026-10-26). Your town may use an older code edition, so ask your building department.
Backfeeding means plugging a generator into a wall outlet, often with a "suicide cord." CPSC calls it "extremely dangerous," because it can electrocute utility workers and neighbors (CPSC). OSHA says never attach a generator to a building's wiring unless a qualified electrician has installed a transfer switch (OSHA).
Your options
Manual transfer switch
A separate switch that feeds selected circuits from the generator. It's simple to use and limited to the circuits it's wired to.
Interlock kit
A listed plate on your main panel that physically stops the main breaker and the generator breaker from being on at the same time. It's usually the lower-cost option. It has to be listed for your specific panel.
Automatic transfer switch (ATS)
Standard with standby generators and many home batteries. It switches over without you doing anything. Standby costs →
Generator inlet box
An outdoor, weatherproof socket for plugging in the generator's cord. It's used with a transfer switch or interlock, never alone. The NEC requires a warning sign at the inlet (702.7).
Portable power stations
Some large power stations sell their own transfer or home panel kits. Otherwise, plug appliances straight into the unit; no house connection is needed. Compare stations →
When you need an electrician
Hire one for anything that touches your panel: transfer switches, interlocks, and inlets. Many towns also require a permit and inspection. Plugging appliances directly into a generator (outdoors, 20+ ft from doors and windows, per CPSC) or into a power station needs no electrician.
Get installer quotes → · Size your backup first with the calculator →
FAQ
Is it legal to backfeed a generator through a dryer outlet?
No. NEC 702.5 requires listed transfer or interconnection equipment, and CPSC calls backfeeding through an outlet extremely dangerous to utility workers and neighbors.
Is an interlock kit legal?
A listed interlock kit for your specific panel is a form of transfer equipment under NEC 702.5. Some towns have extra rules, so check with your building department and use a licensed electrician.
Transfer switch or interlock kit: which is better?
An interlock usually costs less and can feed any circuit in the panel, one breaker at a time. A transfer switch is limited to pre-selected circuits but is simpler to use. An automatic transfer switch is standard with standby generators.
Do I need an electrician to install a generator inlet box?
Yes. An inlet connects to your panel through transfer equipment, which is panel work. Use a licensed electrician and get a permit where required.
Backup power, before the next outage
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