Dear Mr. Electrician: How can I install a Generator Interlock Kit on my existing GE main circuit breaker panel so that I can connect a portable generator to it safely?
Answer: You first must determine if you have the needed circuit breaker spaces for a generator circuit breaker in your main electrical panel. Usually two, but sometimes three spaces are needed. Then you need to order the correct generator interlock kit that is approved for your circuit breaker panel. On newer electrical panels many manufacturers make an accessory interlock kit. If you read the labeling inside of the panel carefully you should see a part number for the interlock kit for your panel. If your main circuit breaker panel is older you might be able to obtain a third party manufacturer interlock kit. The interlock kit shown on this post was made and sold by InterlockKit.com. The photos below depict the interlock kit installation onto a GE main circuit breaker panel that was originally installed in the 1980’s. NOTE: Some text links go to applicable products on Amazon.
Main Breaker Interlock Kit Installation on a GE Load Center
Before beginning the job of installing an interlock kit on an existing main electrical panel, you should apply for an electrical permit at your local building department. Include a copy of the interlock kit installation instructions with your permit application. I always include a brief one page description of the work being done with my permit applications if I cannot fit all of the information on the permit application form. Wording such as “Electrical work consists of the installation of a third party manufactured interlock kit on an existing 150 amp, 30 circuit GE main electrical panel. A new 50 amp sub-panel is to be installed for relocated circuits. Generator inlet to be installed outside next to garage door.” is something that I probably used with the permit application for the installation depicted in this post.
I had a permit application for an interlock kit installation rejected once. After I submitted the paperwork, I received a call from the electrical sub-code official. He said that the state was no longer accepting the laboratory testing results of the third party interlock kit. Consequently I was not allowed to install that particular interlock kit as it would never pass inspection. I contacted the manufacturer and it was confirmed that my state was the only one that was no longer accepting the laboratory testing results from this one particular testing laboratory. The testing laboratory had stopped doing electrical testing, but their previous tests were good. My state would no longer accept even the previously accepted testing. The manufacturer said that they were in the process of paying to have all of their products retested by another testing laboratory that my state would accept.
When I first saw this client’s main electrical panel I noticed immediately that it was overloaded with circuits. The panel was only rated for 30 circuits, but due to the use of twin circuit breakers it contained more than 30 circuits. The homeowner wanted an interlock kit installed so that he could use his portable generator to power certain circuits in his house in the event of a utility company power failure.
The addition of a generator circuit breaker with the interlock kit in this particular GE load center required the use of three circuit breaker spaces. In order to pass inspection a sub-panel needed to be installed so that some of the circuits in the main panel could be removed and relocated. Consequently I also needed two additional circuit breaker spaces for the circuit breaker for the sub-panel.
I had to locate the new electrical sub-panel several feet away from the main panel due to a lack of space next to the main panel. It actually worked out well using EMT conduit to feed the sub-panel and to relocate the existing circuits. You can see my post on electrical conduit types here.
The two pole 30 amp generator circuit breaker needed to be located in the two upper right circuit breaker slots near the main circuit breaker. One additional blank space is required for the operation of the interlock kit. A blank GE circuit breaker filler plate was used to fill in the empty circuit breaker slot.
I had plenty of wall space and ceiling space to relocate some of the existing circuits and to mount the new sub-panel.
It is important to identify the circuits that you will be using the generator for. You don’t want to overload the generator. With the interlock kit you can pick and choose which circuits that you want to use at different times of day. Most people want the refrigerator, furnace, and well pump connected to the generator. Other circuits such as bathroom lighting, water heater, microwave oven, and sump pump are also good choices for generator power during a blackout.
In this particular installation some of the original circuit wiring was fastened to the drywall ceiling. I was able to mount two junction boxes on the ceiling and redirect a few of the existing circuits into the junction boxes. From the junction boxes I pulled single conductors through the EMT conduit down to the sub-panel.
In the 3/4″ EMT conduit for the sub-panel feed from the main panel, I pulled two #6 THWN conductors for the hot line wires. I also pulled in one #8 conductor for the neutral and a #8 grounding conductor. A two pole 50 amp circuit breaker was installed in the main panel for this.
Tools required for this job included a 3/4″ EMT conduit bender, a rotary hammer to drill a hole through the masonry wall to bring the the 10/3 Romex into the back of the generator inlet. An electrician’s hammer, pliers, screwdrivers, awl, razor knife, half round file, and Channellock pliers were all used here. I used my Cordless hammer drill to make holes in the masonry to mount the sub-panel board. I used my cordless impact driver for driving screws into wood and masonry. I also used my cordless hammer drill (In drill only mode) to make holes in the panel cover to attach the interlock kit.
Materials for this job included 3/4″ EMT conduit with set screw connectors, set screw couplings, and straps. Also used was #12 single conductor wire in white, black, and green. 10/3 Romex with ground was used to connect to the generator inlet. Romex staples and BX staples were both used. #6 copper and #8 copper THWN wire was used to feed the sub-panel. A GE sub-panel with no main (Lugs only) was used with 1/2″ and 1″ GE circuit breakers. 4 11/16″ square x 2 1/8″ deep metal junction boxes were used with Romex connectors and 4 11/16″ square blank covers. One Reliance PB30 outdoor generator inlet box was used to connect to the portable generator. Emery cloth was used to clean paint from around the drilled holes in the panel cover for better grounding of the interlock kit.
When installing the interlock kit it is important to follow the instructions from the interlock kit manufacturer. This is necessary for safe operation and also to pass inspection.
Locate the generator inlet where it is convenient to roll the generator to and is not near any windows. You don’t want carbon monoxide getting into the house.
Using an L14-30 generator cord you connect the cord to the generator inlet and to the generator before starting the generator and with the circuit breaker on the generator in the off position. The main breaker in the main electrical panel must be turned off. All branch circuit breakers must be turned off. Start up the generator and then turn on the circuit breaker on the generator. Then turn on the generator circuit breaker in the main electrical panel in the house. Then turn on your previously chosen branch circuits to be powered from the generator.
To see a more detailed interlock kit installation on a Cutler Hammer Load Center, click here
You can see photos of a Square D generator sub-panel installation here