Automatic transfer switches

What the switch does

The automatic transfer switch, often called the ATS, sits between the utility service and your panel. It constantly checks the incoming power. When the power drops, it signals the generator to start, waits until the generator output is steady, and then moves the house to generator power. When the utility returns, it moves the house back and lets the generator cool down.

Just as important, the switch makes it impossible for the generator to send power back out onto the utility lines. Backfeeding is dangerous to line workers and to your own equipment, and connecting a generator without a proper transfer switch or interlock is illegal.

Types of switches

The main choice is how much of the house the switch covers.

• Service-rated switch: installed at the service entrance and sized for your full service, often 200 amps, so the generator can carry the whole panel
• Essential-circuit switch: feeds a small subpanel with the circuits you pick, used with smaller generators
• Load management: modules that work with the switch to hold back big appliances until there is capacity

Installation and permits

Transfer switch work happens at your main electrical connection, so it must be done by a licensed electrician with a permit and inspection. The utility may need to be involved if the meter has to be pulled. In North Castle, the installer files the permit with the town. This is not a do-it-yourself job in any form.

When a switch is replaced on its own

Sometimes an existing generator is fine but the switch is not: it may have failed, be too small for a panel upgrade, or be a manual switch you want to make automatic. In those cases the switch can be replaced without changing the generator, as long as the two are compatible. Ask the electrician to confirm compatibility in writing.

Questions to ask

Ask what amp rating the switch has, whether it is service-rated, whether load management is included, and how the switch will be tested at startup. If you are also adding an EV charger or upgrading the panel, plan all three together so the pieces work as one system.

Questions homeowners ask