Transfer switch installation

What a transfer switch is for

Your house can draw power from the grid or from a generator, never both at once. The transfer switch decides which. In a standby system, it watches the utility supply, starts the generator when the supply fails, and shifts the house over once the generator is ready. When the grid is back and stable, it shifts back.

The switch also protects other people. Without it, generator power can travel backward through your meter onto the street lines. That is called backfeeding, and it can injure or kill utility workers repairing those lines. It can also damage your generator and wiring when the grid returns.

For these reasons, code requires a transfer switch or approved interlock for any generator connected to a home's wiring.

Automatic and manual switches

A standby generator always pairs with an automatic switch. A portable generator pairs with a manual transfer switch or a panel interlock and an outdoor inlet box: you start the generator outside, plug it into the inlet and move the switch by hand. Both setups must be installed by a licensed electrician. A portable generator should never be plugged into a household outlet.

Whole-house or selected circuits

A service-rated automatic switch, commonly 200 amps for a single-family home, moves the whole panel. A smaller switch can feed a subpanel with the circuits you choose. Two-family houses may need a switch for each panel or a plan that covers only one unit. Your installer will recommend a setup based on your service, your panels and the generator size.

Older Ossining panels

Many older village houses have panels that are full, outdated or not suited to a new switch. If yours is one of them, the installer may suggest replacing the panel or upgrading the service at the same time. Doing both together usually means one permit and one shutdown instead of two. See our page on panel upgrades for more.

Licensing and permits

In Westchester County, electrical work must be done by a Westchester County licensed electrician or someone they employ. Transfer switch work also needs a permit and inspection in most villages and towns. Ask the installer to list both in the quote.

• Check the switch amperage and whether it is service rated
• Ask whether load management is included
• Confirm who files the permit and meets the inspector

What happens during an outage

With an automatic switch, you will usually notice the lights go out for a few seconds, then come back as the generator takes over. The switch keeps checking the utility side. Once power returns and holds steady for a set time, it moves the house back and the generator runs briefly to cool down before stopping. Nothing needs to be flipped by hand, which matters if you are away or asleep when the storm hits, and it means a house sitter or family member does not need instructions.

Questions homeowners ask