Generator Interlock Kit for Square D Panels
The right generator interlock kit for a Square D panel depends on two things printed on the panel label: the product line (QO or Homeline) and the series. Square D (Schneider Electric) makes three kits for each line, and some older series have no kit at all, so read the label before you buy anything.
Find the kit for your panel
How the Square D interlock works
The kit is a metal bracket with a sliding arm that sits between the main breaker and a back-fed two-pole branch breaker, which becomes your generator main. The arm only lets one of those two breakers be ON at a time, never both. To switch over, you turn the main off, slide the plate, and turn the generator breaker on.
That's the whole mechanism. No relays, no electronics. It's cheap and it works, but someone has to walk to the panel and do it by hand.
Step one: find your panel line and series
Open the panel door and look for the label on the inside of the door or on the deadfront. You're looking for:
- The line name: QO or Homeline (the breaker handles say QO or HOM too).
- The series code, usually printed near the catalog number.
- The main breaker type and its amperage (the Square D kits are built around a QOM1 or QOM2 main).
- Whether the panel is indoor (NEMA 1) or outdoor (NEMA 3R).
Take a phone photo of the label. You'll want it when you order, and the electrician will want it too.
Homeline interlock kits
These fit convertible Homeline load centers with a main breaker.
| Kit | Fits | Main breaker | Back-fed breaker |
|---|---|---|---|
| HOMCRBGK1C | Series S, indoor (NEMA 1) and outdoor (NEMA 3R) | QOM1, 100 to 125 A | Up to 125 A, and no bigger than the main |
| HOMCGK2C | Series S indoor and Series S1 outdoor | QOM2, 150 to 225 A | Up to 125 A |
| HOMRBGK2C | Series S2, S3 and S4 outdoor | QOM2, 150 to 225 A | Up to 125 A |
Each kit pairs the two-pole main with a two-pole HOM breaker from 15 to 125 A and comes with a retaining kit for that breaker. Homeline Series 1, 2 and 3 load centers have no interlock kit, and neither does any series not on that list. The 60-space models HOM60120M200PC and HOM60120L225PC won't take the HOMCGK2C.
QO interlock kits
The QO kits follow the same pattern for convertible QO main breaker load centers.
| Kit | Fits | Main breaker | Back-fed breaker |
|---|---|---|---|
| QOCRBGK1C | Series G and S indoor, and Series G, S1, S2 and S6 outdoor | QOM1, 100 to 125 A | No bigger than the main |
| QOCGK2C | Series G and S indoor, and Series G and S1 outdoor | QOM2, 150 to 225 A | Up to 125 A |
| QORBGK2C | Series S2 and S6 outdoor | QOM2, 150 to 225 A | Up to 125 A |
No 60-space QO load center has a kit, and the QO160M200P and QO160M200PC can't use the QOCGK2C.
If your panel is main lug only
A main lug panel has no main breaker, so there's nothing to interlock against. Schneider says the convertible main lug versions of these series can be converted to main breaker panels with the matching QOM1 or QOM2 main, and then take the kit. That's an electrician's call, since it changes how the service is protected.
Combination service entrance devices (the meter-and-panel combos common on newer outdoor installs) aren't covered by these kits. If you have one, look at a transfer switch instead.
What else you'll need
The kit is only the lockout. A working setup also needs:
- The two-pole back-fed breaker sized for your generator, held in place by the retaining kit.
- A power inlet box outside, rated to match your generator's outlet.
- A generator cord with the right plug on each end.
Repair parts for the kits aren't sold separately, so a bent or lost plate means buying a new kit. Follow the instructions in the box you buy, because Schneider updates them.
Homeline or QO: does it matter here?
For interlocks, not much. Both lines get the same three-kit layout, and the same "one main at a time" bracket. What matters is matching the exact series on your label. If your panel is an older Homeline Series 1, 2 or 3, there's no kit, and an electrician will usually price a small transfer switch or a panel replacement.
FAQ
How does an interlock kit work?
It's a sliding plate that blocks either the main breaker or the generator breaker, so only one can be switched on. You turn the main off, slide the plate over, and then turn on the generator breaker. Reverse it when the power comes back.
Are there different types of Square D breakers?
Yes. Square D sells two residential lines, QO and Homeline, and their breakers aren't interchangeable. Each line has its own interlock kits, so check which one your panel uses before ordering.
Is Square D Homeline or QO better?
QO is the premium line and Homeline is the budget line, and both are common in US homes. For a generator hookup, the better one is simply whichever you already have, as long as your series has a listed kit.
Can I install a Square D interlock kit myself?
Some homeowners do, but it means working in an energized panel and usually needs a permit and inspection. Hire a licensed electrician who can pull the permit, and expect the inspector to check the job against the kit instructions and local code.
Sources
- Schneider ElectricWhat are the generator interlock kits available for Homeline load centers? (opens in a new tab)
- Schneider ElectricWhat are the generator interlock kits available for QO load centers? (opens in a new tab)
- Schneider ElectricHow does the QO / Homeline generator interlock kit work? (opens in a new tab)