How a Generator Interlock Kit Works
What Is a Generator Interlock Kit?
A generator interlock kit is a mechanical safety device that mounts to the front cover of a residential breaker panel. Its purpose is to allow safe generator backfeeding of your home during a power outage while preventing electricity from your generator from traveling back into the utility lines on the street. This dangerous condition, known as backfeeding, can injure or kill utility workers who are restoring power, and it can destroy the generator itself.
Our Generator Interlock Kits consist of two sliding metal plates held together by bolts, mounted precisely on your panel cover. The plates are engineered to slide in a defined range of motion: enough to block either the main utility breaker or the generator breaker, but never allowing both to be in the on position simultaneously. This mechanical interlock is what makes the device both simple and safe.
GenInterlock kits are developed by a licensed electrician with over 30 years of field experience. Every product in the catalog is designed around real-world panel configurations, tested for fit, and independently certified - not a generic solution adapted from another application.
Ready to find the right kit?
Generator Interlock Kit vs. Manual Transfer Switch
Both interlock kits and manual transfer switches are code-compliant methods of connecting a portable generator to a home's electrical system. Here is how they compare:
| Generator Interlock Kit | Manual Transfer Switch | |
|---|---|---|
| Installation | Mounts to existing panel cover | Separate sub-panel + additional wiring required |
| Existing Panel | Stays in use, no changes needed | Transfer sub-panel added alongside |
| Circuits Available | All circuits in your existing panel | Only dedicated circuits wired to the transfer panel |
| Generator Flexibility | Any portable generator | Fixed; circuits must match generator capacity at install |
| Typical Cost | Significantly lower | Higher (additional materials + installation labor) |
| Code Standard | NEC Article 702 | NEC Article 702 |
| Listing | MET-listed (house-brand kits), UL-listed | UL-listed |
The primary advantage of an interlock kit is that every circuit in your existing panel stays available during an outage. With a transfer switch, only the circuits pre-wired to the transfer panel are accessible. For most homeowners with a portable generator, an interlock kit is the most practical and cost-effective solution.
What's Included with Every Interlock Kit
GenInterlock kits come complete with all hardware needed for installation:
- Generator interlock plate(s), manufactured to fit the specific panel model
- Mounting hardware (screws, drill bit, and Loctite - when applicable)
- Installation instructions specific to your panel manufacturer and model
- MET Lab certification or UL listing documentation where applicable
- Operation / warning labels
Each kit is manufactured to precise tolerances for its specific panel. An imprecise fit is not just inconvenient - a plate that does not seat correctly can allow both breakers to be on simultaneously, defeating the entire purpose of the device. This is why GenInterlock maintains a dedicated catalog for each supported panel rather than offering a one-size-fits-most solution.
Many installations also benefit from a circuit breaker retainer, which keeps your dedicated generator breaker firmly seated in the panel over years of use. It is a small addition that makes a real difference in long-term reliability.
If you still need to connect your generator to the panel, we carry power inlets and cords in a variety of configurations to complete the hookup safely.
How to Choose the Right Kit for Your Panel
Interlock kits are panel-specific. A kit designed for one brand's panel will not fit another's, even if both carry the same amp rating. Here is the process for finding the correct kit:
-
Identify your panel brand/manufacturer.
Open the outer panel door. You do not need to remove the inner cover. The manufacturer name is almost always printed on a label on the inside of the door or on the panel cover itself. Common brands include Siemens, Square D, Eaton, Cutler-Hammer, General Electric, and Murray, among many others. Visit the manufacturers page to browse all supported panel brands. -
Find the panel model number or series.
Typically on the same label as the manufacturer name, the model number helps narrow down the exact kit within a brand's product line. -
Note the main breaker's amp rating.
Usually printed directly on the main breaker handle: 100A, 150A, 200A, and so on. -
Check the main breaker position.
Is the main breaker at the top-left or top-right of the panel interior? Some kits are designed for left-side mains and others for right-side mains. Product listings specify this for each kit.
Once you have these details, browse to your panel manufacturer's page and match your panel to the correct kit. If any step is unclear, contact us and we are happy to help confirm the right fit before you order.
GenInterlock also maintains one of the most comprehensive catalogs of kits for legacy panel brands, including Gould, GTE Sylvania, Westinghouse, and Challenger - panels that are still in service in millions of older homes but are no longer supported by most suppliers. If your panel is older or less common, there is a good chance we have the kit for it.
Code Compliance & Safety
Generator interlock kits are a recognized and code-compliant transfer method under the National Electrical Code (NEC). NEC Article 702, Optional Standby Systems, governs portable generator installations in residential and light commercial settings. A key requirement of Article 702 is that transfer equipment must prevent the simultaneous connection of both the normal utility source and the standby generator source. A properly installed interlock kit fulfills this requirement mechanically: it is physically impossible to have both the main and generator breakers in the on position at the same time.
GenInterlock carries both MET Lab-listed and UL-listed kits across the product line. Independent listing means the product has been physically tested by a recognized third-party laboratory and confirmed to meet applicable safety standards - it is a meaningfully higher bar than a manufacturer simply claiming their product is code-compliant. For jurisdictions that require a listed product for permit approval, this distinction matters. Check with your local authority having jurisdiction (AHJ) for requirements in your area.
Browse our MET-listed and UL-listed generator interlock kits or visit the manufacturers page to find the right fit for your panel.
Why Electricians and Homeowners Choose GenInterlock
Manufactured and independently tested for safety, built to fit your exact panel, and backed by over 30 years of electrical experience.
Designed by an electrician
Every GenInterlock kit is built around real panel configurations by someone who has worked with these panels in the field for over 30 years.
Independently listed
MET Lab-listed and UL-listed kits, independently tested and certified by recognized third-party laboratories - not just claimed compliant.
Panel-specific fit
Kits are manufactured for your exact panel, not adapted from a generic template. The fit is precise because it has to be.
Made in the USA
All our kits are American-made and include the mounting hardware and instructions for your installation, so everything you need arrives in one box.
Legacy panel coverage
We support a wide range of manufacturers, including many older and discontinued panel brands that most other suppliers no longer stock or carry.
Free shipping and warranty
Free standard shipping is included on every order, and every kit is backed by our two-year warranty for real peace of mind.
Using Your Interlock Kit During a Power Outage
Once installed, using the interlock kit during an outage is a straightforward process:
- Position your portable generator outdoors in a well-ventilated area, away from windows, doors, and any exhaust path into the home. Never run a generator indoors or in an attached garage.
- Connect the generator to the power inlet on your home's exterior with the appropriate generator cord, then start it and let it run and stabilize.
- At the breaker panel, turn off any branch circuit breakers for loads you don't need, to stay within your generator's rated output.
- Switch the main breaker off, move the interlock plate over to the generator position, then switch the generator breaker on.
- Restore the branch circuit breakers for the loads you want to run, one at a time.
When utility power is restored, reverse the sequence: turn off the branch circuits, switch the generator breaker off, move the interlock plate back to the utility position, turn the main breaker on, then shut down and disconnect the generator.
Frequently Asked Questions
No. The interlock kit installs directly on the cover of your existing breaker panel. No separate subpanel or transfer panel is required.
No. When running on generator power, all of the circuits in your existing panel remain available. You are limited only by the output capacity of your generator, not by the interlock kit itself.
Yes. The interlock kit is compatible with any portable generator. The connection between your generator and the panel is made through a power inlet and generator cord matched to your generator's plug configuration. We carry power inlets and cords in a range of configurations to complete the hookup.
Yes. When properly installed by a licensed electrician using a listed kit, a generator interlock is a code-compliant installation method under NEC Article 702. Some local jurisdictions may have additional requirements; always verify with your local authority having jurisdiction (AHJ).
Instructions are included with every kit and are also available on each individual product page. For additional help, visit our FAQ page or contact us directly.
Yes. GenInterlock carries MET Lab-listed and UL-listed kits, meaning they have been independently tested and certified by recognized third-party laboratories. These listings are documented and included with applicable kits. Independent certification is separate from a manufacturer simply claiming code compliance - it means the product has been physically evaluated against applicable safety standards by an outside body.
GenInterlock carries kits for a wide range of residential panel manufacturers, covering both current production brands and legacy panels still in service in older homes. Visit the manufacturers page to find your brand. If you're not sure whether your panel is supported, reach out to us and we are happy to help.
Ready to Find Your Kit?
Browse by panel manufacturer or view all of our interlock kits. Free shipping on every order.
Questions before you order?
Contact us at
732-339-4191 or
sales@geninterlock.com.