Sub panel main breaker sizing

1

I assisted on an inspection of a house this week that had a large addition put on it. They had a main (newer) electrical panel in the addition, and converted the old electrical panel into a sub panel (with isolated neutral and ground bus bars.) The breaker in the main panel for the subpanel circuit was a 60 amp breaker, but in the sub panel that main circuit was wired to a 100 amp breaker. So that caused us to have a couple questions. We checked prior topic postings, but they were old and contradicted each other.

  1. Shouldn’t that subpanel breaker be a matching 60 amp breaker?
  2. If it is ok for the breakers to not match, should the subpanel breaker be smaller than the main panel breaker, or should the main panel breaker be smaller?
  3. Or (as stated in a previous topic posting) it doesn’t matter what size the subpanel breaker is cause all it is really doing is providing service as a shut off or disconnect switch?
  4. The wire size was (I forgot, but we looked it up and) and it only supports 65 amps. Therefore, we wrote up that the breaker in the subpanel was oversized for the wire used. Was that correct, or doesn’t it matter what size that subpanel main breaker is?

Thanks.

2
  1. No. See #3.
  2. Yes, no. The breakers do not need to match.
  3. Yes, the 100 amp main CB is fine because the feeder is protected at it’s origin in the other panel.
  4. No. You have a 60 amp feeder that originates at the newer panel. The conductors are 65 amps so they are properly protected.
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3

You have a 60 amp sub panel.

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