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Connecting a Portable Generator to the Home Main Electric Panel – Part 2


If you landed on this page from a search engine, you may want to read my first post, “Connecting a Portable Generator to the Home Main Electric Panel – Part 1″ by clicking (here).


  • ~10 ft of 12/2 (20 amps) or 14/2 (15 amps) cable;
  • Wire nuts
  • Wire cutter
  • One, 2 in. Non-metallic (NM) Sheathed Cable Clamp Connector
  • 36-in. drill bit

Step # 1 – Relocate Existing Breakers

The primary purpose of a backfeed circuit breaker is to stop electricity from your generator to the power grid.

I cannot stress enough that you absolutely need to make sure that your electricity is isolated from the general power grid.

During power outage, there may be multiple lineman working near your house and we want to protect them getting injured or killed by our portable generator.

For my main load panel (Square D, QO series, 200 amps), I needed to free up two 15 amp breaker slots on the right side (just below the main breaker) to install my 60 amp double pole circuit breaker. Because my panel was pretty full, I had to relocate these two breakers to the bottom, left side. This meant I had to splice the extra wires using wire nuts to extend the existing wires to the new location. Please note that not all towns allow this extension method. Contact your local inspector for his/her guidance;

Step # 2- Install Service Cable / Feedback Circuit Breaker

This step routes the service cable from the main panel to the power inlet box. Because I had to install this setup last minute, I simply tacked the cable on to the ceiling. At later time, I will re-route the service cable through the floor joists via the garage attic.

  • First, knock off a hole from the top of the main panel and install a 2-in NM Cable Clamp Connector;
  • Route the service cable through, making sure that it does not touch any parts that are still energized;
  • We want the extra length to be able to route it inside the main panel without any kinks (gentle curves);
  • Attach the white wire to neutral
  • Attach black and red hot wires to the circuit breaker
  • Insert the feedback circuit breaker to the main panel

Step # 3 – Install Power Inlet Box

  • The hole was drilled with a downward angle (approx 15 degrees) to ensure that water will not drip back in to the house (akin to drip loop);
  • Disassemble the inlet box and attach the back bracket to the wall. I inserted a leftover toilet plastic shim between the bracket and wall to angle down the inlet box to minimize water penetration;
  • Add some NOALOX into the wire receptacles and screw down the wires;
  • Space is rather tight inside the inlet box with thick wires. I had to juggle wires multiple times to make them fit;

Step # 4 – Install the Interlock Kit

  • Remove a single screw holding down the main circuit breaker shroud;
  • Attach the metal plate that identifies feedback circuit breaker;
  • Flip the cover panel and line up the screw hole template (making sure that right side is now left side because I reversed the cover panel);
  • Align the plate and lightly drill with a 3/16″ metal drill bit;
  • Flip the cover panel and re-drill the holes using a 5/8″ drill bit;
  • Remove the metal shards from the backside of the panel using a pair of pliers;
  • Line up the interlock slider on the cover panel and install 3 screws;
  • Apply the interlock notification sticker on the inside part of the cover panel door;
  • Test to make sure that the slider moves up and down without resistance;


That pretty much does it for this project. With a manual interlock kit, I am able to manage whichever circuit I want to supply power to without worrying about overloading the portable generator. Not as convenient as the standby generator, but I am not a big fan of all the electronics in such units so this setup works for me.

If you have any questions, please leave a comment below.

Thanks and good luck with your DIY project!

Chad P

Thursday 11th of June 2020

How did you deal with the bonded ground in your breaker box? I've got a similar setup and it causes a ground-fault condition in my generator. I've tried removing the ground bond in the generator, but that did not fix the problem.


Thursday 11th of June 2020

Hi Chad-

It's been some time since I did this project. I believe the setup was:

exterior plug - accepts 3-wire connection (black, red, white) main electric panel - neutral bonded to panel (ground) 4-wires connect from the main to sub subpanel - neutral bus bar is NOT bonded to panel (isolated from ground)

Working with subpanel and main panel is quite dangerous so if you are absolutely not sure what you are doing, please consult with an electrician.


Rick Conti

Friday 30th of August 2019

Jim, thanks for the article! I'll be using it to install a kit in my house. Here's a recap and a questions. So, the main function of the kit is to protect Power Company workers from getting electrocuted from a home owner backfeed. Secondly, to make it easier on the homeowner to power up needed appliances during a power outage. The scenario is you've lost main power to your house and the interlock kit is going to make you place the main breaker disconnect in the off position before placing the backfeed breaker in the "On" position. So, before you turn on the backfeed breaker, which will become the feed to the breaker box buss, wouldn't you want to turn off all the other breakers in the box first, then turn on your backfeed breaker and then sequentially turn on the breakers needed to support you emergency condition? It's my thought if you don't do it in that fashion you may cause a current surge and trip the backfeed breaker or overload the generator or both? Am I missing something in your article? I know that's the way I'd power up what I needed. Thanks, Rick


Sunday 16th of September 2018

What did u do with the ground wire from generator to panel?


Monday 17th of September 2018

Hi Brian-

Service cable connecting from the inlet to the panel has 3 conductors (red, black, bare ground). ground conductor was attached to the main panel's ground bus.

Hope that helps.


Friday 20th of July 2018

Do you have any problems with tripping of any gfi circuits in house or tripping of generator gfi while also using 30a circuit?


Tuesday 28th of August 2018


I have not experienced any GFCIs tripping when using my generator

Alyce Sanders

Wednesday 11th of October 2017

I am planning to buy a generator and put it over my house. I am worried on what to buy a gasoline one or the diesel one. I also want to buy a quit generator and not the one that will bring noise all over the house.


Wednesday 11th of October 2017

@ Alyce-

A standby generator almost always is powered by natural gas so I am going to assume that you are referring to portable generators.

Diesel gennys are more fuel efficient and has longer equipment lifetime (more durable) BUT it costs about 3-4 times more and depending on where you live, diesel might not be readily found.

Gas gennys are less fuel efficient and may require more maintenance BUT it is heck of a lot cheaper than diesel generators and gas can be found anywhere.

I would say that both types generate a fair amount of noise, though some say diesel produces louder sound. I will be encasing my portable generator in a housing (article will be published shortly) which will reduce the noise.

Regardless of what you choose, I think having it tie into the main load panel is the way to go.

Good luck!