Multiple OCPD

[VIC1958]

Scenario: Older commercial building currently being serviced by 100 amp service. 100 amp panel on interior with 100 amp OCPD. This panel is feeding nothing else but a new panel in the basement. Conductors that feed the new panel to the old panel are sized to 200 amp. Conductors from old panel to meter box and meter box to transformer are rated 100 amp. The owner of the building is working with utility company on possible upgrade of transformer so he can eventually upgrade his service. (The current transformer is maxed out).
Question: In order to keep tenants who occupy the building from overloading the service, is it required that the NEW panel have a 100 amp OCPD along with the older panel? Or can they put a 200 amp OCPD in the new panel and leave the 100 amp breaker in the old panel? I hope I explained it correctly.

 

[Dennis Alwon]

If the conductors going from the 200 amp panel to the old 100 amp panel are rated for 200 amps then there should be no issue as the 100 amp breaker will control the load. Now if you can add to the 200 amp panel then all bets are off.

I am assuming a new 200 amp panel feeding an old 100 amp main breaker panel-- is that correct?

 

[VIC1958]

The original 100 amp panel is feeding the newer panel in the basement. The older panel has a 100 amp breaker. Conductors from this 100 amp original panel are rated to 200 amps. Does it matter if they put a 100 amp or 200 amp breaker in the new panel, as long as they leave the 100 amp breaker in the original panel? Calculations show that they are at the max. for a 100 amp service.

 

[ActionDave]

The original 100 amp panel is feeding the newer panel in the basement. The older panel has a 100 amp breaker. Conductors from this 100 amp original panel are rated to 200 amps.

Dennis answered your question starting from the new panel back to the old. The set up you describe is fine. You can protect the 200A wire with a 100A breaker.

Does it matter if they put a 100 amp or 200 amp breaker in the new panel, as long as they leave the 100 amp breaker in the original panel? Calculations show that they are at the max. for a 100 amp service.

As long as the conductors are properly protected at the supply (line side) you can land them in whatever size breaker you wish. If there is any capacity for new loads is a different issue, but NEC load calculations are very conservative.