What Is a Generator Interlock Kit (and Is It Safe)?

Fall is the quiet window before Oklahoma’s power goes out. The ice storms that take down lines and leave neighborhoods dark for a day or more are still a couple of months off, which makes right now the easy time to sort out how you’d actually run a generator before you need it. A call we start getting every October is from homeowners who’ve bought — or are about to buy — a portable generator and want to connect it to the house the right way, but balk at the price of a full transfer switch and ask whether an interlock kit is a safe shortcut.

It’s a good question, and the answer is yes — with real conditions attached. Here’s what an interlock kit is, how it stacks up against a transfer switch, and how to tell which one belongs on your panel.

What an Interlock Kit Actually Does

An interlock kit is a small, engineered metal plate that mounts on the front of your electrical panel. It works together with two breakers: your main breaker and a dedicated generator (backfeed) breaker installed at the top of the panel.

The plate slides up and down, and it’s shaped so that only one of those two breakers can be switched on at a time. When the main is on, the plate covers the generator breaker and you can’t turn it on. To use the generator, you switch the main off first — which disconnects your house from the utility — and only then can you slide the plate over and energize the generator breaker. That physical either/or is the entire point.

Because the generator feeds the panel through that backfeed breaker, power flows to your regular circuits. So instead of wiring a few pre-chosen outlets, you can pick and choose from your actual breakers — run the furnace blower, then switch some of its capacity over to the refrigerator or the well pump — as long as you keep the total within what your generator can handle.

Interlock Kit vs. Transfer Switch

Both solve the same core problem: connecting a generator to your home’s wiring without the two power sources ever meeting. They just go about it differently.

• A transfer switch is a separate box, usually mounted beside the panel, pre-wired to a fixed set of circuits you choose at installation — say, the furnace, the fridge, a few lights, and the sump pump. During an outage you flip its switches and those circuits run on generator power. An automatic version (paired with a standby generator) does it all by itself within seconds, even when you’re not home.
• An interlock kit uses your existing panel rather than adding a second box. It’s generally the lower-cost option for a portable generator because it’s less hardware, and it gives you flexibility to manage any breaker in the panel — but it relies on you to switch the main off, start the generator, and manage the load manually every time.

The short version: a transfer switch is more hands-off and purpose-built; an interlock kit is more economical and flexible but asks more of the operator. Neither is a “suicide cord” — plugging a generator straight into a wall outlet to backfeed the panel, which is the genuinely deadly shortcut both of these exist to replace.

Is It Safe and Up to Code?

A properly done interlock installation is safe and legal. The National Electrical Code allows interlock devices specifically, and the key requirement is that the kit be listed for your exact panel — not a generic plate drilled on to fit. That listing is what guarantees the mechanical lockout actually works and that the panel keeps its safety rating.

Connecting a generator to home wiring is permitted electrical work in Oklahoma, interlock or transfer switch alike. The permit and inspection aren’t red tape; they’re the check that the backfeed breaker is sized correctly, the inlet is installed and bonded right, and the lockout can’t be defeated. Where interlocks get a bad name is the improvised ones — a mismatched kit, a homemade plate, or an install with no permit — because those are exactly the setups that can fail and let the generator backfeed onto the utility lines. Done to code, it does the opposite.

Which One Is Right for Your Home?

An interlock kit tends to be the better fit when:

• You have a portable generator you’ll roll out and start by hand.
• There’s a listed kit available for your panel’s brand and model.
• You want the flexibility to run different circuits at different times rather than a fixed set.
• You’re comfortable switching the main off and keeping an eye on your total load during an outage.

A transfer switch tends to win when:

• You want the simplest possible routine during a stressful outage, or an automatic standby system that runs itself.
• Your panel isn’t compatible with any listed interlock kit.
• You’d rather have a fixed, pre-balanced set of essential circuits so there’s nothing to think about at 2 a.m. in an ice storm.

There’s no single right answer — it comes down to your panel, your generator, and how hands-on you want to be when the lights go out.

Why This Is Pro Work

Whichever route you choose, the connection itself isn’t a DIY project. The installer has to confirm there’s a listed kit for your panel, add a correctly sized backfeed breaker in the right spot, mount a weatherproof generator inlet, bond and label everything, and pull the permit so it passes inspection. Get the breaker size or the panel compatibility wrong and you’ve either got a connection that won’t carry the load or one that isn’t truly locked out. Our team handles whole-home and portable generator hookups — interlock kits and transfer switches both — sized to your home and installed to current Oklahoma code.

The Bottom Line

A generator interlock kit is a legitimate, lower-cost, code-approved way to power your whole panel from a portable generator — as long as it’s a kit listed for your specific panel and it’s installed and permitted by a licensed electrician. It trades the hands-off convenience of a transfer switch for a lower price and more flexibility, with the catch that you manage the main breaker and the load yourself. Both are far safer than the dangerous wall-outlet backfeed they replace, and fall is the right time to put one in — long before an outage forces the decision.

If you’re planning how to run a generator this winter, the licensed electricians at Graco can look at your panel, tell you whether an interlock kit or a transfer switch is the smarter fit, and install it safely. We serve Edmond, Oklahoma City, Norman, Moore, Yukon, Guthrie, and the surrounding metro, with flat-rate pricing you approve up front before any work begins. Call (405) 500-5333 and get it handled before the first ice storm does.