Generator Interlock Kits: Find the Kit for Your Panel

How a generator interlock works

Every panel interlock does the same job. A metal slide or bracket mounts on the panel cover or the breakers, between the main breaker and a two-pole breaker that becomes the generator main. The slide lets only one of those two be on at a time. Siemens describes the purpose plainly: preventing dangerous feedback between two power sources.

Using it in an outage goes like this, per GE's instructions: main off, branch breakers off, slide the plate toward the main, generator breaker on, then turn on the circuits you need one at a time. When the power comes back, reverse it. There's nothing automatic about it, and that's why it's cheap.

Interlock kit vs transfer switch

Both are legal ways to connect a portable generator. The interlock uses your existing panel, so any circuit in it can run on generator power, as long as you watch the load. A manual transfer switch is a separate box with a set number of pre-picked circuits. For most homes with a portable generator and a panel that has a listed kit, the interlock is the better value. Our interlock vs transfer switch page goes deeper.

Find the kit for your panel brand

Panel makers build interlocks for their own current lines, and aftermarket makers fill in the older panels.

Factory kits from the panel maker

• Square D, split into Homeline and QO kits matched by series number.
• Eaton BR and CH kits, including plug-on neutral versions. The CHMIKCSR, for example, is a 225 A interlock for CH load centers with CSR or CSH mains.
• Cutler-Hammer, Eaton's older brand, with notes on older CH layouts.
• Siemens ECSBPK kits, chosen by breaker type and main rating.
• GE, where the factory THQLLX1 is listed for Model 6 PowerMark Gold load centers.

Older panels, mostly aftermarket kits

• Murray, often sharing kits with Siemens and ITE layouts.
• Bryant, where the panel's condition matters as much as the kit.
• Westinghouse panels.

What to read off your panel

Before you click a brand, open the panel door and photograph the label. Write down the brand and line, the series or model, the main breaker's amp rating and catalog number, and whether the main sits at the top, the bottom, or down in the branch spaces. For older panels, also measure the gap between the main and the breakers next to it. Interlock Technologies asks for exactly that photo and gap to match a kit.

30 amp or 50 amp?

Kits advertised by amp size are usually an interlock plate bundled with a back-fed breaker and inlet of that size. The plate itself doesn't care about the generator size. Interlock Technologies pairs a 30 amp back-feed breaker and inlet with generators up to 8,000 watts, and a 50 amp setup with larger units. Match the cord and inlet to the largest outlet on your generator. The generator cords page covers plug types.

Installation: what's involved

An electrician installs the back-fed breaker in the spot the kit calls for, secures it with a retainer, mounts the plate, and runs wire to an outdoor inlet box. GE's kit, for instance, has the cover drilled from a template and the back-fed breaker held by a bolted retainer. Siemens notes its kits take up the two spaces beside the breaker they lock, and those spaces can't take filler plates. So plan on losing a couple of branch spaces.