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Generators, Backfeed and the Lineworker

Reference Resilience Updated Oct 28, 2026

Why this matters

Every big outage produces the same setup in a few houses on your route: a portable generator in the garage or under a window, a homemade cord with a plug on both ends, and that cord pushed into the dryer receptacle so "the whole house works." It does work, which is why people keep doing it. It also turns the house wiring into a source that can push voltage back out through the meter, up the service drop and onto the utility line a lineworker believes is dead, and it puts an engine making carbon monoxide inside or against the house. A field tech who walks into this during an outage is often the only trained person who will see it before the power comes back.

What backfeed is, and how a house becomes a power plant

Backfeed is current flowing from a source on the customer's side of the meter back toward the utility. In a normal house, power flows one way: utility transformer, service drop, meter, main breaker, panel bus, branch circuits, loads. A generator connected to a branch circuit reverses the direction from that circuit upward. If the main breaker is closed, nothing stops the reversed flow at the panel, and the generator is now connected to the utility's transformer.

The transformer does not care which side the power comes from. It steps voltage up just as readily as down. A typical overhead distribution transformer feeding a few houses might be rated for 7,200 V on its primary and 240 V on its secondary, a ratio of 30 to 1 (illustrative; ratings vary by utility and circuit). Push 240 V from a generator into the secondary, and the primary rises toward 7,200 V. The lineworker up the street who opened a switch and is working the line without grounding it at that spot is in contact with a conductor the generator has energized.

 BACKFEED PATH, main breaker left ON

 generator --> double-male cord --> dryer receptacle
                                         |
                               30A breaker in panel
                                         |
                                   panel bus
                                         |
                       main breaker (CLOSED) <- the gap
                                         |
                                       meter
                                         |
                                 service drop
                                         |
                  transformer secondary, 240 V
                                         |
                  transformer primary, ~7,200 V
                                         |
                 line "out" for repair, crew on it

Two other hazards in the same cord. The plug on the dryer end of a double-male cord has bare, energized prongs whenever the generator runs and the other end is plugged in, so anyone who pulls it out of the receptacle is holding a live plug. And when utility power returns with the main closed, the generator is suddenly connected to a much larger source out of phase. The generator, the cord or the panel can fail violently, and the house wiring may carry fault current it was never sized for.

Lineworkers are trained to treat every line as energized and to ground lines at the work location (OSHA's 29 CFR 1910.269), and that practice is what keeps most backfeed events from killing someone. It is a defense that depends on every crew doing it every time; a homeowner's cord should not be the reason it is tested.

What the code requires instead

NEC Article 702, Optional Standby Systems, as adopted by your jurisdiction, covers generators that a homeowner chooses to install for convenience. Section 702.5 requires transfer equipment for a standby source connected to premises wiring, and that equipment has to prevent the normal and the standby sources from being connected to each other at the same time. In practice a portable-generator hookup that meets it is built from one of the first two pieces below, usually fed through the third.

  • A transfer switch, manual or automatic, that switches selected circuits (or the whole house) between utility and generator. It is mechanically built so it cannot connect both.
  • A listed interlock kit on the panel: a sliding plate or bracket that makes it physically impossible to turn on the generator's backfed breaker while the main breaker is on. It must be listed for that specific panel, and the backfed breaker has to be secured with the additional fastener the NEC requires for backfed breakers (408.36(D) in recent editions).
  • A power inlet box outside the house, with recessed male prongs, so the generator connects with a cord whose plug goes into the generator and whose female connector goes onto the inlet. Every energized contact is shrouded. The inlet still needs the transfer switch or interlock behind it.

Installing any of these is electrical work, and in most jurisdictions it needs a licensed electrician and a permit. Many utilities' service rules (their tariff, the terms a customer accepts by taking service) also prohibit connecting a generator without approved transfer equipment, and some states have statutes that make a customer liable for injuries caused by backfeed. Those rules vary by state and utility; the code requirement is the floor that holds wherever the NEC is adopted. This is not legal advice.

Generators that connect through cords to appliances only (the refrigerator plugged into the generator's own receptacle with an outdoor-rated cord) do not backfeed, because nothing connects to the house wiring. That is the safe portable setup, and for many customers in a short outage it is all they need.

Carbon monoxide: placement is the whole control

A portable generator engine produces carbon monoxide (CO), an odorless gas that kills by displacing oxygen in the blood, and it produces enough to be lethal in an enclosed space within minutes. The CDC's guidance is consistent and specific:

  • Never run a generator inside a home, garage, basement, crawlspace, shed or other enclosed or partly enclosed space, even with doors and windows open. A half-open garage door is an enclosed space for this purpose.
  • Place it outdoors more than 20 feet from the house, with the exhaust pointed away from doors, windows and vents.
  • Install battery-powered or battery-backup CO alarms in the home.

Wet weather pushes people to move the generator into the garage or under an overhang. That is the most common setup behind generator CO deaths after storms. A generator tent or canopy listed for that use, in the open and far from the house, is the answer to rain.

Worked example: an outage call with a generator running

Day two of an ice-storm outage. A tech arrives at a house for a furnace that will not run "even on the generator." The tech's personal CO monitor alarms in the kitchen next to the door to the garage. In the garage, with the overhead door raised about two feet, a portable generator is running. A cord runs from its 240 V receptacle to a plug pushed into the dryer receptacle.

First, the air. The CO monitor sets the order. The tech tells the homeowner, "Your generator is putting carbon monoxide into the house. Everyone needs to step outside now, and I'm going to shut it off." The family goes out to the driveway, upwind of the garage. From outside, the tech lifts the overhead door fully and waits a minute for the garage to air out, then steps in only as far as the generator, for a short entry with the monitor in view, and turns it off at its own engine switch without touching the cord or the plug. Had the monitor still been climbing at the garage opening, the tech would not have gone in: everyone stays out and the fire department is called. Then, outside: "Is anyone dizzy, headachy, sick to their stomach, or more tired than they should be?" One child has had a headache since morning. The tech calls 911 and says a family has been exposed to generator exhaust and a child has a headache. CO poisoning looks like the flu, and the person who seems fine can be the one who is not; that is for the responders to assess, not the tech.

Second, the backfeed. With the generator off, the tech checks the panel: the main breaker is ON. Had the utility restored the line, or had a crew been working the line without grounding it at that spot, the generator was connected to both. The tech switches the main to OFF, then unplugs the double-male cord from the dryer receptacle only after confirming the generator is off and its engine is stopped, because with it running those prongs are live.

Third, the conversation. Once responders have cleared the family (the family's doctor or the medics decide when people go back in, and the house is ventilated with doors open and the CO monitor reading near zero before anyone stays inside):

TECH: I'm not going to hook that cord back up, and I'd ask you not to either. With the main on, it was feeding the utility line, which can kill a lineworker. With the generator in the garage, it was feeding the house.

OWNER: So I can't use the generator?

TECH: You can, out in the yard, 20 feet from the house, with the appliances you need plugged straight into it. Or an electrician can put in an inlet and an interlock so the furnace runs on it the right way.

The tech writes on the ticket what was found, what was done, that 911 was called, and that the backfeed cord was left disconnected. If the utility asks customers to report backfeed setups, the shop's practice is to tell the customer that it does, rather than to report a customer behind their back without telling them; the owner can decide that policy with their own counsel.

What would have changed the order. If the CO monitor had read nothing and the generator had been 25 feet out in the yard, the backfeed would have been the first hazard, handled the same way: generator off at its switch, main breaker off, cord out last. If the customer refuses to shut the generator off while it is in the garage with people inside, the tech leaves the house, keeps the family outside if they will come, and calls 911.

The failure mode. The sibling case card, The Dryer-Cord Generator the Tech Unplugged, follows a tech who pulled the plug first. The live prongs were the injury.

What a tech checks on any outage call with a generator on site

  • Where is the generator, and how far from the house? CO monitor on and reading before going inside.
  • How is it connected: cords to appliances, an inlet, or into a receptacle?
  • If there is transfer equipment, is it listed and installed, or improvised? Is the interlock plate present and engaged?
  • Is the main breaker position consistent with the generator being used?
  • Is there a working CO alarm in the house?

References

  • CDC carbon monoxide poisoning prevention guidance for portable generators
  • NFPA 70 (NEC) Article 702, 702.5 transfer equipment, and 408.36(D) backfed devices, as adopted by your jurisdiction
  • OSHA 29 CFR 1910.269, electric power generation, transmission and distribution (lineworker grounding practice)
  • See related: The Dryer-Cord Generator the Tech Unplugged; Homes with Solar, Batteries or Generators Already Installed; Generator Sizing + Selection Reference

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