Why You Need a Generator Interlock and How to Install One


Do you have a portable generator? Perhaps you've bought one for camping or outdoor events. It's also likely that you purchased a generator so that you can have electricity when the utility power fails, either as the result of storms or unexpected interruptions to the power grid.

That's great, but have you given any thought to how you'll get power from your generator to the devices and branch circuit breakers in your home where you'll need it? In this article, we'll examine one common way to have your generator feed your home with power safely during an outage by installing a generator interlock switch on your main breaker panel.

Table of Contents

  • Powering your home with a generator
  • Generator safety
  • Why choose an interlock kit?
  • Are generator interlock kits safe?
  • Are generator interlock kits legal?
  • How do you pick the right generator interlock kit?
  • Step-by-step instructions

Powering your home with a generator

A generator is a useful source of backup power for emergency use. There are several different ways that a generator can be used to supply power to your home.

Back-up generator

Backup or whole-house generators are mounted permanently outside of your home and hardwired into the home's electrical circuits. They often utilize triggers to turn on automatically when the power goes out and use natural gas or diesel fuel for power. You can learn more about the advantages of backup generators in this article.

Portable generators

Smaller gasoline-powered generators can serve multiple purposes and are useful for providing power to portions of your home when the electricity goes off. There are three ways to connect a portable generator to your home's electrical circuits.

  • Extension cords. If you're using a small generator and are only concerned with powering a few appliances (like a refrigerator or freezer), you can plug them into the generator's power outlets with the use of extension cords.
  • Transfer switches. A transfer switch is a comprehensive way to utilize a generator in your home. A separate breaker panel is installed next to your main panel. When utility power fails, the generator is plugged into a dedicated outlet and electricity flows into the transfer switch to branch circuit breakers in the breaker panel. The separate panel prevents backfeeding of the power main from your generator.
  • Generator interlock kit. A generator interlock kit provides the same level of safety as a transfer switch but is less expensive and easier to install. A set of metal or hard plastic guards allows power to enter the circuit accepting power from the generator while keeping the main switch off.

Generator safety

We've touched upon the dangers of backfeed when using a portable generator, but there are some other dangers that must be considered when using a generator for your home.

Carbon monoxide

Portable generators produce carbon monoxide, a colorless and odorless gas that can cause death in high enough concentrations. Carbon monoxide levels can accumulate in enclosed spaces, so you should never run your generator in the garage, other enclosed spaces, or near open windows. This fact sheet from the CDC reiterates the dangers of carbon monoxide when using a generator.


Backfeed occurs when the main circuit breaker for your home is still on and power is being fed into the home through the use of a generator. This can create the potential for electrical shock to linemen working on the power lines outside your home. Transfer switches and interlock kits prevent backfeed.

Why choose an interlock kit?

When an interlock switch is properly installed, it prevents the generator circuit breaker and the main circuit breaker from both being on at the same time. An interlock kit is a safe and cost-effective way to ensure you're using a portable generator safely.

Are generator interlock kits safe?

When you install a generator interlock you eliminate the biggest danger you can create when you connect a generator to your home's circuitry - the danger of backfeeding power into the mains from generator power. This can also be accomplished with a transfer switch, but a generator interlock kit is less expensive and easier to install.

Are generator interlocks legal?

Generator interlock kits are legal throughout the United States. However, there are some important points to consider.

Many jurisdictions require that interlock kits be installed to match local building codes. Consult with your local government to see what local regulations are regarding generator feeding.

Your local jurisdiction may require that a professional electrician install the kit. Be sure to check local regulations when considering generator interlock installation.

Generator Interlock

How do you pick the right generator interlock kit?

A generator interlock kit is a mechanical device. For the interlock switch to work properly, it must fit your electrical panel properly. When shopping for an interlock kit, you'll need to know the following information.

Note the location of the main breaker. Is the breaker centered, or offset to the right or left? In addition is it at the top, or in line with the other breakers?

Record the amperage of the main breaker.

Measure the gap between the main breaker and the branch breakers.

Now note which way the breaker is thrown. Does the switch move right to left or up and down?

With this information, you should be able to find the correct interlock kit when shopping either at a store or online. In fact, some online stores will guide you through this process step by step so that you'll be confident that you've gotten the right interlock kit.

Step-by-step instructions

Once you've gotten the correct interlock kit, it's time to install it on your breaker box, so you can use generator power safely in your home. It's important to note that every interlock kit is different, and the best way to properly install your specific kit is to carefully follow the instructions and documentation provided with it. With that said, here are some general guidelines for how your installation should proceed.

  1. Open your kit, then read any documentation, identify and separate the parts of the kit before you begin.
  2. The tools you'll need should be listed in the documentation. Make sure you've got everything you need ready to go.
  3. Turn off the main breaker switch.
  4. The front of the breaker panel cover is usually held on with Phillips screws or bolt-head screws. Be cautious when you remove the front of the panel and don't touch any bare wires.
  5. Take the panel cover to your workbench and place it face down. Line up the interlock kit and mark the position of the screw holes. Drill the holes out with the size drill specified in the instructions.
  6. Flip the panel over and mount the interlock kit to the panel with the screws included with the kit.
  7. Position the panel cover back onto the breaker box and reattach using the hardware you removed. When the cover is secure, you can turn the main breaker back on.

Using the generator interlock switch

Once you install a generator interlock switch, the operation will be simple and foolproof.

When you have a power outage, go to the circuit breaker panel and adjust the interlock switch so that you can turn off the main breaker. This will position the interlock switch plate so that the switch for the generator breaker is set to the on position.

Plug your generator into the outlet associated with your generator breaker, and then start the generator.

Now that power is flowing into the system, you'll be able to turn breakers that supply your home on and off so that power flows to where you need it.

Count on us for help with your emergency power needs

Having a plan for backup power for your home when the utility feed fails is a smart idea. And there are many ways to achieve this, including backup whole-home generators. However one of the most economical ways to provide power is with a portable generator.

Using a generator is not without risk. You must ensure that your generator is properly placed to avoid carbon monoxide poisoning, and it must be connected to your home so that the electrical current doesn't backfeed into the power grid.

A generator interlock kit is an economical and safe way to ensure that you can use a generator without risk. And with proper preparation and some careful work, installing one on your breaker panel is a job that's within the skill of the average do-it-yourselfer.

If you're unsure that installing an interlock kit is something you want to handle, or you want to look into other options for providing backup power to your home, contact us, and we'll be happy to talk about the options that are available to you.

 If you're in the Dallas Fort Worth area Contact us for all your plumbing, HVAC, roofing, and electrical needs. Remember, estimates are always free!

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3 comments on “Why You Need a Generator Interlock and How to Install One”

  1. Hello:
    I have decided to invest in a generator but before I do, I need th4 electrical components installed. After reviewing the interlock option, I want to go with it but the main question is my 100 amp box is full. I used the last spot when I installed my central air. What options do I have to secure space for the 30 amp breaker?Thank you

    1. Hey Mark, Most brands of Panels make Tandem breakers that can be used to convert two single pole breakers into a single slot. These can be used to make room in your panel for additional circuits. If you have any other questions please give us a call at 817.888.8880 to speak to one of our electricians.

  2. I have a Honda EU 2200I Gen. My panel is a Square D homeline with 1 3/8" between main and 30amp double pole breaker in top right position. Since the install requires a double pole breaker, how would I wire the breaker with only 3 wires coming from the gen? [one hot. one neutral, and one ground.] Wouldn't this only feed one buss in my panel?
    I have another 20 amp double pole breaker which feeds my refrig. and My kitchen lighting. These circuits share a neutral. How would that work with just one buss being powered. Thanks
    Dave DeCicco


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