Generator Interlock Kit vs. Transfer Switch

Interlock kit vs. transfer switch: which one do you need?

Both do the same safety job, so pick by who’ll be running it at 2 a.m. An interlock kit is cheaper and more flexible, because you can power any circuit in your panel. A manual transfer switch is simpler to operate and harder to overload, because it only feeds a few circuits chosen at installation.

October is Santa Ana wind season, and that means the chance of a public safety power shutoff in parts of Southern California. If you own a portable generator, you probably want it running your fridge and lights instead of a tangle of extension cords across the kitchen floor. Either device gets you there legally.

The one job both devices do

Each one makes it physically impossible for your generator and the utility to feed your house at the same time. That prevents backfeed, where generator power flows out through your service and onto the utility lines. Backfeed can electrocute a utility worker repairing those lines, and it can destroy your generator when grid power comes back.

Never use a double-male “backfeed” cord, and never plug a generator into a dryer outlet. It’s illegal, and it kills people.

How each option works

Interlock kit

An interlock kit is a sliding metal plate on your panel. It lets either the main breaker or the generator breaker be on, never both. You’ll need a generator breaker added to your panel and a power inlet box on the outside wall where the generator cord plugs in.

During an outage, you turn the main off, slide the plate over and switch on the generator breaker, then bring circuits on one at a time. Any circuit in the panel is fair game, up to what your generator can carry.

One catch: the interlock has to be the one listed for your exact panel model. Kits don’t exist for every panel, and older or obsolete panels may not have one at all.

Manual transfer switch

A manual transfer switch is a separate box mounted next to your panel. The circuits you choose, often 6 to 10 of them, are wired through it. When the power goes out, you flip those switches to generator. Many models have meters that show how much load you’re pulling.

The trade-off is that you can only power the circuits picked at installation. That limit is also the feature: it’s hard to overload the generator when only the essentials are connected.

(An automatic transfer switch is a different animal. It pairs with a standby generator, senses the outage and switches over by itself.)

Who manages the load at 2 a.m.

With an interlock, you do. Say you’re running a 7,500 watt generator and someone turns on the AC while the dryer is going. The generator stalls, and now you’re out with a flashlight sorting out breakers. If the person on duty is comfortable with that, the interlock’s flexibility is worth a lot. If not, the transfer switch’s short list of circuits is the kinder setup. Our guide on what size generator you need helps you match those circuits to your generator’s output.

What either setup requires

Both need an inlet box, the right generator cord, a generator with a 240-volt outlet, and a permit. An electrician also checks that your generator’s grounding setup suits the equipment. Infiniti Electric is licensed and insured, and we handle the permit and installation for backup generator connections in Riverside and across the Inland Empire.

Before the next shutoff, get in touch with us and tell us your generator’s size and which circuits matter most.

Generator interlock and transfer switch questions