50 amp breaker at main feeding a 100 amp sub panel

From an electrician friend I have been told it is ok to have a lower amp breaker at the main panel for a wire that feeds a larger main breaker at the sub-panel. I am wondering why this is and what gauge wire should be feeding the main breaker of the sub-panel. The home I inspected today had a 50amp in the main going to a 100 amp main breaker in the sub. This was set up with a 100 amp gauged wire. Would a breaker blow at the sub-panel end, but not in the main panel? Does this setup
work and why? Thanks for your time. Kaitlan

The only issue you may have is if the 50 amp is not sufficient amperage for the subpanel needs.
Other than that, it is a non issue, because the subpanel is protected by a 50 amp breaker, not a 100 amp. The 100 is merely a disconnect at that point.


As Daniel stated your 100 amp sub panel is actually a 50 amp panel. And to answer your question the smaller breaker, the 50 amp breaker, will trip first.


With a 50 amp OCPD ahead of the sub-panel feeder the conductors would normally be #6 AWG for NM cable. For other wiring methods (MC cable, conduit, etc.) #8 may also be code compliant.

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