Fire Pump Bus calculation

[JDBrown]

When a fire pump is installed on a separate breaker ahead of the main breaker as permitted by 695.3(A)(1), how does that affect the sizing of the switchboard bus?

I'm checking over a set of plans for a main switchboard with 1600A bus and 1600A MCB, plus a 600A CB for a fire pump connected ahead of the main breaker. Theoretically, then, the bus could see up to 2200A before either the main or the fire pump CB trips. This doesn't sit well with me, even knowing that the fire pump should only operate in an actual emergency. To my way of thinking, either the MCB should be reduced to 1000A or the bus should be increased to 2200A, so the sum of the MCB and the fire pump CB doesn't exceed the bus rating... but I can't find anything in the code to support this.

So, am I just being overly cautious and it's fine as designed? Can you give me a code reference to show that the design needs to be changed?

(By the way, I'm in California, so I'm using the 2019 CEC, based on the 2017 NEC.)

 

[augie47]

Looks like a violation of 695.3(A)(1) !!

 

[david luchini]

Seems like its permissible per 230.90(A) Ex No. 3., if the calculated load is not more than 1600A.

 

[JDBrown]

Looks like a violation of 695.3(A)(1) !!

Can you clarify how it violates 695.3(A)(1)? The fire pump's CB will be in a separate switchgear section ahead of the MCB, which appears to comply with the first part of 695.3(A)(1). The second part of the paragraph references three other sections, but I don't see a violation of those, either (230.82(5) - taps only supply the fire pump; 230.2 - separate service allowed for fire pump; 230.72(B) - fire pump disconnect installed remote from main building disconnect).

Is the argument that the proposed arrangement would violate 695.3(A) because the power source isn't considered reliable if the bussing could fail from overload?

 

[JDBrown]

Seems like its permissible per 230.90(A) Ex No. 3., if the calculated load is not more than 1600A.

Thank you! Finally, a code section that seems to apply. I was beginning to think it simply wasn't addressed.

 

[augie47]

When I read your post it did not appear to satisfy:
from a connection located ahead of and not within the same cabinet, enclosure, vertical switchgear section, or vertical switchboard section as the service disconnecting means.