Transfer switches

The job a transfer switch does

In a standby system, the automatic transfer switch watches the utility supply around the clock. When the supply drops, it tells the generator to start, waits for steady output, then shifts your circuits to the generator. When utility power returns and stays steady, it shifts back and the generator runs a short cool-down before stopping.

The switch also keeps the two power sources apart. Generator power that leaks back through your meter onto the street lines can injure or kill a lineworker who believes the line is dead. This is called backfeeding. A properly installed switch prevents it, and code requires one for any generator connected to a home's wiring.

That protection is why transfer switches are not optional on any generator tied into a house.

Automatic, manual and interlocks

Standby generators use automatic switches. Portable generators use either a manual transfer switch or an interlock kit on the main panel with an outdoor inlet box. With those, you start the portable generator outdoors, plug it into the inlet and move the switch or breakers yourself. Any of these must be installed by a licensed electrician. Never connect a portable generator by plugging it into a household outlet.

An interlock is often the lower-cost choice for portable generators.

Whole panel or selected circuits

Switches come in two broad types. A service-rated switch, commonly 200 amps on a single-family home, transfers the entire panel. A smaller switch serves a subpanel holding only chosen circuits. In a two-family house, each panel may need its own switch, or the plan may cover one unit only. Your installer matches the switch to the service, the panels and the generator.

Older panels

Rivertown houses with older or crowded panels may need panel work before a switch can be added. If an upgrade is needed, pairing it with the switch installation usually saves a permit and a shutdown. See electrical panel upgrade for details.

Ask the electrician what brand and age your panel is and whether it can accept the switch as is.

Licensing and permits

Transfer switch work happens at the main electrical service, which makes it licensed work. In Westchester County, electrical work must be performed by a county-licensed electrician or someone they employ, and villages and towns generally require a permit and inspection.

• Ask for the switch amperage and whether it is service rated
• Ask whether load management is built in
• Confirm who files the permit and meets the inspector

What you notice during an outage

With an automatic switch, the lights go out for a few seconds, then return on generator power. When the grid comes back, there is another short blink as the house moves back to utility power. Nothing has to be flipped by hand, which matters if you are away, asleep or out of town when a storm hits.

Questions homeowners ask