selective coordination

[binwork91]

BL-170 feeds panelboard with branch breaker BL-171. BL-171 is in series with downstream breaker BL-172


These are emergency loads.


Question:
Does BL-172 need to coordinate with BL-170?


My opinion is no, because BL-171 will trip before BL-170.


But my coworker has a different opinion. He says yes, because the code states:

700.27 Coordination. Emergency system(s) overcurrent devices shall be selectively coordinated with all supply-side overcurrent protective devices.

His argument is that all supply-side, means BL-170 is a supply-side device relative to BL-172.


What do you think?

 

[JoeStillman]

I agree with your co-worker. The mis-coordination between BL-172 and BL-170 would cause the loss of power in the MLO panel and any other branches fed from there. You can't rely on BL-171 to provide the coordination with BL-170 for BL-172.

 

[ron]

The only exception is if there are 2 breakers in series and either opening will be the same outage, then they do not need to be selective with each other, but they both would need to be selective with the one above them.

 

[binwork91]

Thank you

 

[wenify]

I agree with your co-worker. The mis-coordination between BL-172 and BL-170 would cause the loss of power in the MLO panel and any other branches fed from there. You can't rely on BL-171 to provide the coordination with BL-170 for BL-172.

The only exception is if there are 2 breakers in series and either opening will be the same outage, then they do not need to be selective with each other, but they both would need to be selective with the one above them.

Hi all, I’m adding my two cents here for discussion.

Are you suggesting that because BL-171 might fail to trip, BL-170 must coordinate with BL-172? But, the code would consider the system acceptable even without BL-170. We need to agree that all protective devices are functioning properly; otherwise, the entire exercise becomes moot.

There is no other branch offs between BL-171 and BL-172. If a fault occurs at MCB, either or both BL-171 and BL-172 will detect it, race to trip, and de-energize MCB. The MLO would remain energized. Are you suggesting that selective coordination is not achieved because the feeder C-95 becomes involved as well? The only advantage I see in having BL-172 trip before BL-171 is reducing the amount of troubleshooting required afterward.

Please correct me if I am wrong in my thinking.