Is a Generator Interlock Kit Legal?

Power outages are an all-too-common occurrence for many people, and they can completely throw your life out of balance. You may be without power for an extended period, and it can be hard to know when you’ll be able to use your creature comforts again. 

For this reason, many people purchase generators to power their abodes during a power outage. When there is no power, a generator interlock kit is useful for keeping the house powered by a generator.

To allow the generator to power the house, homeowners will often install a generator interlock kit, which allows a generator to power an entire domicile rather than only devices directly plugged into the generator. 

However, there are legal questions about the use of generator interlock kits, and we will look at how they are installed, how much they cost, and their legality depending on where you live. 

Electric generator on a table

What Is a Generator Interlock Kit?

Homeowners install a generator interlock kit directly on a circuit breaker panel. Simply put, they power a house safely by a generator during a power outage. 

By using these kits, you can change the power source to your house in a power outage. Interlock kits also prevent the power from back-feeding into the main power lines.

Without a device like an interlock kit, homeowners won’t be able to run a house with generator power. Instead, they will have to plug in individual devices to a generator for use. 

Manually plugging in multiple appliances is impractical and time-consuming. Instead, interlock kits allow you to switch from your main power to generator power in seconds.

In Which States Are Interlock Kits Legal?

These kits have some legal troubles, and prospective users should research if the devices are permitted to use in their area. However, interlock kits are legal in most states in the United States, assuming they meet a critical distinction. 

All interlock kits should meet approval by the UL under standard UL 67. Some states may require a professional trained in the National Electrical Code and National Fire Protection Code to install the devices. 

Before purchasing a kit, you should ensure that the device is compliant with UL 67. The company you are buying it from should mention in the product description if the device is legal in your area. 

When in doubt, it never hurts to check with a knowledgeable electrician to make sure your interlock kit is both legal and safe to use. 

Why Are Interlock Kits Illegal in Some Areas?

An electrical regulatory authority representative may ask you to remove an interlock kit when inspecting your house. The considerable risk involved is with back feeding, and if not handled correctly, it can cause injury to anyone working on an electrical system. 

There are also fears about the danger of users manually removing an interlock kit. For example, if you take the panel off and the mainline is connected at the same time as a generator, it can damage the generator by overloading the device. It could also harm the mainline if disconnected improperly. 

Still, interlock kits are generally thought of as safe when properly used. But you should always check the device’s legality in your area before purchasing and installing one.

How To Connect a Generator to a House With an Interlock Kit

Certain states will require you to hire an electrician to install an interlock kit. But if you live in a state that allows it, you can install the device yourself. If you’d like to see a video of the installation process, you can watch this one. But we will take you through the steps for installation.

Step 1: Panel Removal

Remove your panel cover using a screwdriver. Determine where you will install the kit and prepare a 5/32 drill bit and an impact driver with a 5/16 nut driver bit. 

Step 2: Drill Holes

Grab a woodblock around 1/2 inch thick and put it under the drilling area. Use the 5/32 drill bit to drill the mounting holes. File the burrs off before proceeding to the next step. 

Step 3: Bracket Installation

Place the bracket aligned with the holes and use the impact driver to install the screws. Ensure the panel is tight to the panel cover.

Step 4: Panel Cover Reinstallation

Once you’ve installed the kit, reinstall the panel cover. When you finish that, you should post the instructions on the panel cover door, ensuring they are always handy when you need to consult with the manual.

Generator Interlock Kit Compatible with Square D QO or Homeline 150 or 200 amp panels. 1 3/8 inches Spacing between main and generator breaker, Professional and Interlock Kit

How Much Does It Cost To Install an Interlock Switch?

A typical kit can cost anywhere from $50 to $150, depending on the manufacturer and the included features. 

If you are installing it yourself, you won’t need to factor in the cost of hiring a professional. Anyone installing it with professional help will have to consider the added costs of an electrician. 

What Are the Alternatives to Interlock Kits?

Interlock kits are one of the two main ways to power a house with a generator in the event of a power outage. The other method is transfer switches. Unlike interlock kits, transfer switches have no legal hangups, and electricians consider the devices safer to use. 

You may be asking yourself, can I use an interlock instead of a transfer switch? Interlock kits are a cheaper option than transfer switches, but you should ensure they are legal to use in your area before purchasing a kit. Transfer switches also have less risk of being misused and damaging a generator.

Pros and Cons of Using Interlock Kits

As with any device, interlock kits have several positive and negative qualities.


  • The kits are cheaper than transfer switches. Interlock kits cost around $50 to $150, while a transfer switch can cost homeowners anywhere from $500 and $1,500.
  • Interlock kits are generally less space-consuming and easier to set up than transfer switches.
  • These kits provide flexibility to users, allowing you to choose which circuits to power with a generator.


  • The kits may not be legal where you live.
  • While still okay to use, interlock kits are not as safe as transfer switches.
  • Misuse may cause damage to the generator or the main power line.

Interlock FAQ

As with any electrical issue, there are bound to be questions regarding interlock kits. Here are a few important questions regarding generator interlock kits. 

Do generator interlock kits meet the code?

If the manufacturer labels the kit as being compliant with UL 67, they are safe to use.

Are generator interlock kits safe?

These kits are safe with proper use. However, misuse or improper installation can cause damage to generators or injury to line workers due to back feeding. 

Are generator interlocks required?

Generator interlocks are one of two main methods used to power a house with a generator. You will need to use either an interlock kit or a transfer switch.

Can I use an interlock instead of a transfer switch?

If it is legal in your area, an interlock kit is an acceptable alternative to a transfer switch. Switches can be expensive for homeowners, and interlocks represent a cheaper alternative.

Installation of a Generator Interlock Kit

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