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I’m looking to add a 30 amp double pole back feed breaker to my home electrical for emergency backup via a portable generator. My current system has a 6 throw panel off the meter powering all of the big ticket items (dryer, ac, range) that I would not want to power with a generator as well as a 100amp breaker powering a sub panel inside my garage with all of the normal branch circuits for the home.
I want to isolate the sub panel in an emergency and back feed just that sub panel with the generator when needed. Current sub panel is a main lug type Eaton ch 125 amp 32 space panel (Eaton AC-5641 / panel board C2233). So currently no main to isolate the panel with an interlock.
So question is which is the best way to go about this? Can I convert/ add a main breaker to my existing sub panel (ie, is the panel convertible to a main breaker type to use as a cutoff from utility line) and use a standard interlock kit, or can I add a 100amp breaker to “back feed” the panel from the utility service and interlock that with my emergency generator breaker? Or any other suggestions?
Goal is to minimize work (not pull meter and/or rewire an entire panel if unnecessary; but want to do this to code without cutting corners. Thanks.

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  • Can you post photos of the labeling on the inside of your existing interior panel's door please? – ThreePhaseEel Feb 20 at 1:01
  • I just added pics from all of the information stickers inside and out that I could find. Thanks everyone for the replies/help – Eraubusy Feb 20 at 1:46
  • Can you try retaking the photo of the labeling on the inside of the front cover? It's too small/blurry to be of any use – ThreePhaseEel Feb 20 at 2:07
  • I just tried to add a new pick of the panel cover, hopefully this one is a little more readable – Eraubusy Feb 20 at 2:31
  • There should be one more label on the inside left or right of the breaker box, can you get us a photo of that label as well? – ThreePhaseEel Feb 20 at 2:45
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You've got a very good grasp of the situation already. At a high level the options would be

  • add a main breaker to the existing panel
    • if one is available
    • if a compatible interlock kit is also available
    • if you make room in that already-full panel for a backfeed generator breaker
  • replace the existing panel with one equipped with a main breaker and more room
  • or, add another panel.

Personally I'd lean toward the latter. Choose a panel that has a main breaker, feed-through lugs, and supports a generator interlock. Insert it so that the existing meter-main panel feeds into the main breaker of this new panel, then power the existing subpanel via the feed-through lugs of the new panel. If a panel with feed-through lugs is too difficult to find then the existing subpanel could instead be fed through a branch circuit breaker in the new panel.

This arrangement buys you a bunch of empty slots for future circuits, the opportunity to put the panel in a more convenient place if desired, and minimizes change to what already exists.

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  • Thanks, it’s hard to see, there are currently 5 spaces still available in that sub panel which would make it possible to add a double pole 100amp for use as a main and a double pole 30 amp to use as a back feed, would almost max out the panel but would fit. Is there a way to look up if the panel can accept a main breaker at the top (ie is it convertible to main breaker?) that would be my first choice as it leaves some empty space for future expansion....or would I need to abandon the main lugs and just feed the panel through a 100 amp breaker? – Eraubusy Feb 20 at 1:01
  • I don’t know of a mechanical interlock for a rule of 6 panel. Really it would not be much different you would lockout the breaker feeding the lower section and then add a breaker in the lower section to back feed from the alternate power source. One may be out there, but if not a main breaker sub panel with the circuits you want to power moved over would be my choice for a not two expensive way to do it or the top shelf upgrade to the main panel itself. Since cutler hammer is a good brand I would probably choose the sub panel method, some other brands I would go with the main panel upgrade.+ – Ed Beal Feb 20 at 6:38
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Interlocking this panel is going to be...tricky, but you can try it

The good news is that fitting your panel with a backfed main breaker and interlock should be possible. You'll need to move the breakers in the four top leftmost spaces down to spare spaces in the panel, then fit a CH2125 and a CH230 up there along with a CH125RB retainer to hold the CH2125 down. With the breakers fitted, you can then move the incoming feeder hots over to the CH2125's lugs, making it a main disconnect for your panel. Finally, a CHML mechanical interlock is used to make sure you can't turn the CH2125 and CH230 on at the same time. Once that's done, you can run some 10/3 cable to a 20A or 30A, 4-prong inlet box on the outside of your house, so that you have a legal and safe place to plug the generator in at, and then you can go generator shopping.

HOWEVER: it'll limit your generator selection

The bad news is that going with a generator interlock on this panel limits your choice of generator vs. breaking the standby loads out into a separate generator panel. This is because a generator interlock kit, when fitted to a "normal" panel like yours, can't switch neutral between the utility and generator sources, which matters because there only can be one active neutral-to-ground bond in your electrical system, and many portable generators supply one themselves so that they can meet OSHA regulations for safe use on worksites. Or in other words, without that switched neutral, your generator needs to not provide a neutral-to-ground bond, since your main panel is already providing one for you.

As a result, you'll have to be careful when generator shopping to get a generator with a floating neutral, or at least one which provides instructions for removing the neutral-to-ground bonding wire from it. Note that you won't be able to use such a generator for portable applications, but given your situation, that may very well be an acceptable tradeoff.

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