Generator backfeeding and interlock kits: what's safe and what needs an electrician
Backfeeding means pushing generator power into your house wiring through an outlet, usually with a male-to-male cord. The CPSC calls it extremely dangerous because it can electrocute utility workers and your neighbors. The safe ways to run house circuits from a portable generator are a transfer switch or an interlock kit, installed by a licensed electrician.
Published , by Alex Rowan
Review pending. This page hasn’t been checked by a licensed electrician yet. Until it is, treat your owner’s manual and the sources at the end as the final word.
What backfeeding is
A portable generator has outlets meant for extension cords. Backfeeding connects one of those outlets to a wall outlet or a dryer outlet, so the generator’s power flows backward through the house wiring. It takes a cord with a plug on both ends, often called a suicide cord.
Why it’s dangerous
- It can kill line workers. The CPSC says backfeeding “presents an electrocution risk to utility workers and neighbors served by the same utility transformer.” The transformer that steps utility voltage down for your street works in both directions, so it can step your generator’s 240 volts up to thousands of volts on a line a crew believes is dead.
- The cord itself can electrocute you. Once one end is plugged into the generator, the prongs on the other end are live and exposed. In 2026 the CPSC told consumers to stop using male-to-male cords and throw them away, and got Walmart, eBay and AliExpress to remove listings.
- It bypasses protection. The CPSC notes that backfeeding skips some of the home’s built-in circuit protection devices.
- The generator can be destroyed when the grid comes back. Honda’s manual warns that with an improper connection the generator “may explode, burn, or cause fires when utility power is restored.”
- It brings the generator close to the house. The CPSC says the short length of these cords leads people to run generators in enclosed spaces or too close to the home, which raises the carbon monoxide risk.
Switching off the main breaker first doesn’t make a suicide cord safe. It still leaves live exposed prongs, it depends on nobody forgetting the breaker, and it still skips the protection devices.
The two safe ways: a transfer switch or an interlock kit
The National Electrical Code (NFPA 70) covers home generator connections in Article 702, optional standby systems. Section 702.5, as quoted from the 2017 edition in IAEI Magazine, requires transfer equipment designed and installed to “prevent the inadvertent interconnection of normal and alternate sources of supply.” In plain terms, the house can be connected to the grid or to the generator, never to both at once. NFPA’s own generator tip sheet says that if you connect a generator to house wiring, a qualified electrician should install a properly rated transfer switch in line with the NEC and your state and local codes.
Two kinds of equipment do this for a portable generator.
| Transfer switch | Interlock kit | |
|---|---|---|
| What it is | A separate switch, often with its own small panel of circuits | A plate or slide on your existing panel’s cover |
| How it works | Each circuit switches between grid and generator | The main breaker and the generator breaker can’t both be on at once |
| Circuits you can power | The ones wired into the switch | Any circuit in your panel, as long as the total stays within the generator’s output |
| Safety standard | UL 1008, transfer switch equipment | Evaluated as a panelboard accessory under UL 67 |
| Which one fits | Mounts on the wall beside the panel and connects through a knockout. Limited to its number of circuits and its generator rating | Only a kit listed in your panel’s markings |
The standards and panel markings come from UL’s explanation in IAEI Magazine. Interlock kits are panel-specific: a panel that can take one is marked for use with a particular kit, and that’s the kit to install.
A manual transfer switch is sized differently. Reliance Controls’ instructions for its kits describe a switch mounted about 18 inches from the panel, wired in through a knockout with a flexible conduit, and listed to UL 1008. Each kit handles a set number of circuits, and each switch circuit has to match the breaker size of the house circuit it’s connected to. The same manual says the switches work with generators up to 8,000 watts continuous that have a 20 or 30 amp twist-lock outlet. Check those limits against your generator before you buy.
The power inlet
Either setup usually comes with a power inlet box mounted on the outside wall. You park the generator at least 20 feet away and connect it to the inlet with a generator cord that has a female connector on the house end. The inlet has the male prongs, and they’re inside a housing, so no live prongs are exposed at any point. It’s the safe replacement for the suicide cord.
What needs an electrician
All of it. Honda’s manual puts it this way: connections to a building’s electrical system “must be made by a qualified electrician,” must isolate generator power from utility power, and must comply with all applicable laws and electrical codes. Honda also says to consult the utility company or a qualified electrician before making any connection.
When you hire someone, ask about:
- the permit and inspection your city or county requires for the work;
- whether your panel has an approved interlock kit, or whether a transfer switch is the better fit;
- the inlet and cord rating that match your generator’s largest outlet;
- how your generator’s neutral and ground are set up, which your electrician needs to check for this kind of connection;
- whether your utility wants to be told about the connection.
Plan which circuits you’ll run
A transfer switch or interlock kit doesn’t make the generator any bigger. With an interlock, you can switch on any breaker, which makes it easy to overload the generator. Before the outage, list the circuits you’ll turn on and add up what’s on them.
The table on this page shows sourced figures for common essentials. A well pump often runs on 240 V and has a large startup surge, so it sets the minimum generator size for many homes. A gas furnace needs power for its blower. The runtime calculator adds up the load and the startup surge for everything you pick.