Generator Transfer Switches & Backfeed
During outages, some people plug a generator into a wall outlet with a "male-to-male" cord. This can send electricity back out to the power lines, which can electrocute utility workers and neighbors. A properly installed transfer switch prevents this.
- Homeowners
- Electricians
- Contractors
What is backfeed?
- When a generator feeds a building's wiring that is still connected to the utility line, the power can flow backward through the service transformer and step up to thousands of volts on lines believed to be dead.
- Line workers and anyone touching a downed line can be killed. See Downed Power Lines.
- Backfeed can also damage the generator and cause fires when utility power returns while the generator is connected.
Safe connection methods
- Transfer switch: a device that physically disconnects the house from the utility before connecting the generator. It can be a manual or automatic switch for selected circuits or the whole panel.
- Interlock kit: a mechanical device on the main panel that prevents the main breaker and the generator breaker from being on at the same time. It must be approved for that panel.
- Generator inlet box: a weatherproof inlet installed on the outside wall, connected to the transfer switch, so a cord can plug in without running through windows.
- Or plug appliances directly into the generator using outdoor-rated extension cords. See Extension Cords.
- Never use a male-to-male cord or "suicide cord" to plug the generator into a household outlet.
- Never connect a generator to a panel without a transfer device.
Installation
- Hire a licensed electrician and get a permit and inspection. See DIY Electrical Work
- Size the generator and switch for the circuits you plan to run; start-up surges for motors can be several times running watts
- Follow rules for grounding and neutral bonding (portable generators have different configurations). See Grounding & Bonding
- Install the inlet where the generator will be placed outdoors, away from windows, doors and vents
- Label the panel, and test the system before the next storm
Run it safely
- Run generators only outdoors, at least 20 feet from the building, with the exhaust pointed away. Carbon monoxide kills. See Portable Generators and Power Outages & Generators.
- Install battery-powered carbon monoxide alarms.
- Refuel only when the generator is off and cool.
Standards & references
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