A generator transfer switch closes off the utility power line to your home’s electrical system during a power outage and opens a line to a generator, then reverses the process when grid power is restored. Permanently hard-wired to and installed near the breaker panel in your home, transfer switches solve the problem of backfeeding, which occurs when electricity runs backward out of the house and through the utility transformer.
Per the National Electrical Code (NEC), all transfer switches must have a three-position “LINE-OFF-GENERATOR” or “ON-OFF-ON” switch to keep power from accidentally backfeeding. The three-position switch ensures that the switch goes through the off position when traveling from the generator position to the line position, fully disconnecting the generator every time before the main utility switch is turned on. To learn more about generators, see our Generators Buying Guide.
Many areas require a transfer switch to be installed by a licensed electrician. Be sure to check local electrical codes before installing one yourself.
This buying guide will explain the two different types of transfer switches so you can feel confident you’re choosing the best switch to keep your essential appliances running safely during a power outage.
Factors to Consider
• Types - Manual, automatic
• Options - Pre-wired, inlet box, outdoor switches, maintenance and testing
Manual transfer switches are hardwired to your control panel and used to power portable or optional standby generators. Manual switches must be manually turned on and off when the electricity goes out or comes back on, which can be a problem if you aren’t home during a power outage. The switch is wired to essential circuits in your home, such as lights and furnace blowers that can’t be run with an extension cord.
Automatic transfer switches automatically turn the generator on and switch power to it when they detect a drop in line voltage and turn the generator off when they sense the line power is restored. Automatic transfer switches can be used with portable generators as long as the generator has an electric starter. They are most often used with automatic standby generators, the permanently installed generators that look like central air conditioning units.
Pre-wired transfer switches come with all of the wiring you need to connect the switch to the main breaker panel. All you need to do is attach the conduit to the main box, pull the wires through the conduit and wire the circuits on the transfer switch to the breakers on the main panel representing the circuits you want to power with the generator.
An inlet box, mounted to an outside wall and hard-wired to a cord-connected transfer switch, keeps you from having to run the heavy-duty generator extension cord into the house to power the generator.
Outdoor transfer switches must be encased in weatherproof housing. They are installed on an outside wall as close to the main breaker panel as possible.
Maintenance and testing must be done on a regular basis, consult your transfer switch manual for manufacturer’s recommendations, so you can be sure your generator will work properly every time it is needed.