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Alright, folks.

I screwed up and overlooked part of this project before I started.

I have a 200a residential main panel. I installed a 150a subpanel 10 ft away to isolate service for a basement suite I’m building. I know that to pass inspection, the breaker feeding my subpanel needs to match or exceed the amp rating of the subpanel itself. However, the apparent latest breaker this 200a main panel will physically fit is 125a. I’ve installed it. Everything works as expected, but I’m stuck as to what to do to pass inspection.

Any helpful suggestions you’d like to share?

Happy to share all my load calculations and such but I’m hoping for a solution that doesn’t force me to replace one of these panels entirely.

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  • The sub panel is fine. The problem might be the 125 amp breaker on a 200 amp panel. It might be too big. You only have 200 amps total, so might be leaving the rest of the house with only 75 amps. Have you done a load calculation yet? Imagine the inspector might be interested in it.
    – crip659
    Commented May 7 at 11:13
  • What you think you know is utterly backwards.
    – Ecnerwal
    Commented May 7 at 12:37
  • Thanks so much! All of this makes sense. Commented May 9 at 10:54

3 Answers 3

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I know that to pass inspection, the breaker feeding my subpanel needs to match or exceed the amp rating of the subpanel itself.

This is incorrect "knowledge" and it is exactly the wrong way around.

The feeding breaker must protect the sub-panel and the wiring connecting it to the main panel from overheating due to too much current flowing through them. That protection only happens if the breaker is smaller or equal to the amp rating of the sub-panel.

If your sub-panel also has a main breaker on it, that breaker can be any size you want it to be, because the function of that breaker is only to act as a disconnect, an easy way to remove all power from the sub-panel. It does not need to protect against over-current.

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Actually, this is wrong. If the sub panel has its own main breaker, than it can be higher, lower or the same amperage as the feed breaker in the main panel. The feed breaker protects the feed wires while the sub panel main breaker protects the sub panel itself.

On the other hand, if the sub doesn’t have a main breaker, the feed breaker must be less than or equal amperage than the sub panel rating to protect the sub panel.

What you have is fine.

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You said "I know that to pass inspection, the breaker feeding my subpanel needs to match or exceed the amp rating of the subpanel itself."

Not true.

The feed breaker's purpose is to protect the conductors and equipment from overcurrents. You won't be able to load the sub-panel beyond 125 amps. If that works then you are good. As long as the feed breaker protects your wiring and the panel then you are good. Which means it cannot exceed the rating of the conductors or the panel. @Bart is correct the main in the sub-panel is just a disconnect now.

If you wanted to get the full 150 amps for that sub-panel you would have had to install a 200 amp feed-thru main panel since most manufacturers don't make a 150 amp breaker for a branch circuit. Just main breakers.

@DoxyLover is also correct you are fine with what you have.

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