Are Generator Interlock Kits Legal?

Chloe Meltzer
by Chloe Meltzer
Power outages are simply the worst. Power is necessary in all areas to keep your home or business running smoothly. So what do you do when your power goes out? You could use a generator interlock kit, but are they legal? Follow along as we explore the regulations that often come along with using an interlock kit.

Today, we’re answering an important question for anyone living in an area that sees a lot or power outages: are generator interlock kits legal?

Your power never goes out at a convenient time. Not only does power keep your home’s temperature regulated, but it runs your refrigerator, too. In some cases, it will also help keep any necessary medical devices on. The bottom line is you need reliable power to keep your home running smoothly.

So, what do you do if your power goes out? The best option for anyone who experiences frequent power outages and does not have a permanent standby generator is to purchase either a transfer switch or a generator interlock kit. The problem with transfer switches is that they are expensive, leaving a generator interlock kit as your best option.

Generator interlock kits come with many regulations but are legal in the United States as long as you follow all codes that protect against over-currents and have a functioning backup system that can support the backup generator. In some jurisdictions, you may need a professional to do the work, so you should make sure you can install it on your own.

This article will cover what a generator interlock kit is, how it compares to a transfer switch, and how to install one. Additionally, we will talk about the electrical codes involved and what you need to know before deciding to use one.

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A Bit About Generator Interlock Kits

Generator interlock kits are devices designed to power a home through a portable generator during a power outage safely by connecting the generator to the existing electrical system. It is an affordable alternative to a transfer switch.

An interlock kit prevents the main breaker on your electrical control panel from being turned on at the same time as your generator breaker. It makes it so you cannot operate your panel’s main cutoff switch. When you are using your generator, it also prevents power from being back-fed into the power lines. This is important because it can injure whoever is working to repair your mainline power.

In generator mode, the back feed breaker is on. This means that it is accepting power from the generator into the panel. In this case, though, the main breaker is off, which keeps the external mains separate. At this point, you’ll be able to turn on any individual breakers you need. The only one that must stay off is the main breaker.

Once power is restored, all you have to do is turn off the individual breakers and slide the interlock kit back down to cover the generator breaker. This will expose the main breaker once more. After turning that back on, you can turn on each breaker once more. Be sure to unplug the generator power cord and return the generator once you’re done using it.

A Bit About Transfer Switches

Also known as an automatic transfer switch, these devices transfer power supply. They take power from its primary source to a backup generator through a separate set of circuit breaker switches. These devices activate when they sense a power outage or failure in the primary source.

By flipping the switches you can isolate entire circuits from the main breaker and into the generator. Although transfer switches are beneficial, they are also very expensive and more difficult to install.

Pros Of Using A Generator Interlock Kit

Before purchasing any device, you should understand the advantages. That way, you can see if it’s a good fit for what you’re trying to accomplish. The same goes for getting an interlock kit. So, here’s what you should know. Generator interlock kits are…

  • Convenient. Interlock kits do not require a separate panel to operate. Instead, they are installed directly onto your home breaker panel.
  • Affordable. These kits are very cost-effective, typically ranging from $50 to $150 per kit. Conversely, a transfer switch can cost anywhere from $500 to $1,500.
  • Flexible. You’ll be able to choose which electrical circuits are powered by the generator. This offers much more freedom than a pre-wired transfer switch.
  • Efficient. Some interlock kits have a “utility power return alert.” This will let you know when the power has returned, and you can stop using your generator interlock kit.

What To Be Aware Of When Using A Generator Interlock Kit

To make an informed decision about your purchase, it’s not enough to just know the advantages. So you can better understand what you’re buying, we’ll briefly go over all the things you must consider.

  • Checking for power. When your electrical panel is in interlock mode, you will need to figure out when the power is restored on your own. If your interlock kit does not have a “utility power return alert,” then you will have to figure this out for yourself by checking periodically.
  • Modifications. Although installing a generator interlock kit is simple, additional modifications may be needed within the electrical panel to ensure it works properly. You must also make sure you have enough circuit breaker spaces in your current panel.
  • Overloading. In a standard interlock kit, there is nothing to prevent you from turning on extra circuit breakers. This can overload your generator, which can be dangerous for those in your home and any workers operating on the power lines. It can also damage the interlock kit itself.
  • Other risks. Without the front panel cover, you run the risk of being able to turn on both the main and generator breakers. This can be incredibly dangerous for any utility workers 

Electrical Codes For Generator Interlock Kits

Generator interlock kits are legal as long as they are installed and maintained according to code. Here are the codes you must specifically follow.

US NEC 702 Optional Standby Systems

This code requires that the standby or backup system can support the selected loads. These loads are in accordance with the amount of power that needs to be maintained by the backup generator. Standby electrical systems have the option to include legal systems, optional standby systems, and backup systems. Although both legal and optional standby systems are included in the NEC Chapter 7 Articles 701 and 702, backup systems are not.

In order to be up to code, your generator interlock kit must allow only one of the breakers to be in the “ON” position at one time. This meets the requirements of Article 702 of the National Electrical Code ANSI/NFPA 70.

US NEC 408.36 Overcurrent Protection of Panelboards

Specifically, electrical panelboards must be protected from over-currents by a single device. This must be either be located ahead of the panelboard, within the panel board, or at any point on the supply side of the panelboard.

One specific section is good to note:

“Each lighting and appliance branch-circuit panelboard shall be individually protected on the supply side by not more than two main circuit breakers or two sets of fuses having a combined rating not greater than that of the panelboard.” – US NEC 408.36

As long as you install the breaker retaining strap, you will appropriately meet the requirements of Article 408.36.

How To Install A Generator Interlock Kit

Interlock generator kits are legal even if you install them on your own, but you can also hire an electrician to do the work. In some jurisdictions, you may actually be required to hire a professional. Here are the steps that you must take if you decide to tackle the project on your own.

Step 1: Remove The Panel

First, you will need to remove the panel cover using a Phillips screwdriver. Next, you will need to drill holes into the panel using a 5/32 drill bit and an impact driver with a 5/16 nut driver bit or flat bit. Depending on the type of panel, you will drill in the middle mounting holes or the outside mounting holes.

Step 2: Drill Holes

You will need a block of wood that’s about 1/2″ thick and put it under the area you’re going to drill so that you don’t hit the panel door. Then, using the 5/32 drill bit, you will drill the four mounting holes. Before continuing, file off the burrs so that the bracket mount is tight to the panel cover.

Step 3: Install The Interlock Kit Bracket

Now you need to hold the bracket inside the panel to align the mounting holes. Next, grab the impact driver that has the 5/16 nut driver and install the shorter screws. The bracket should be nice and tight to the panel cover.

Step 4: Reinstall Panel Cover

Now that you have mounted the kit bracket, you will need to reinstall the panel cover using the six-panel screws. However, the number of screws will differ depending on the type of panel you have.

Step 5: Post The Instructions

You should have two decal stickers, one is a yellow one, and the other is white. The yellow is the operating instructions, while the white one helps you identify the manually interlocked breaker. You should put the instructions on the door to the panel cover, so they’re easily readable. Place the white sticker next to the interlocked breaker.

If you’d rather, you can always trip the bottom part off so that you can stick the decal onto the breaker itself. However, this is entirely up to you. Next to the breaker will work just fine.

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Our Takeaway

Generator interlock kits are legal, as long as you install it according to code. Some jurisdictions require you to hire a professional; however, this usually isn’t the case regarding generator interlock kits. Either way, you will need to check your local laws regarding this matter before beginning this project on your own.

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Chloe Meltzer
Chloe Meltzer

Real estate agent and copywriter, originally from California. Chloe brings her real estate expertise into her writing to create effective and helpful home guides for you! When not writing or selling homes, she spends her time as a digital nomad traveling the world.

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