NEC 2020, 240.86(C)

[curious101]

Hello,
Question regarding the above listed code section. I have a case where in the main distribution panel (MDP), a 225A/3P circuit breaker (feeding a 10kAIC MLO panel which has motors on it) is series rated with the upstream 65kAIC, 800A service disconnect with overcurrent protection. Roof top units are fed off the MDP and some condensing units off some panels fed from the MDP. Does the sum of the motor full load Amps - per the above mentioned NEC section - include all the motors in the 10kAIC panel and the roof top units and the condensing unit motors too?
I have read some posts on this code section, but it seems to me that NEC 2020 has different wording than the previous NEC versions, so it would be nice to get clarification.
Please let me know if you have any questions.
Thanks, and have a great day!

 

[mayanees]

Yes, if I understand your description correctly. The wording did change slightly in the 2020 edition, but the application is the same.

 

[curious101]

Yes, if I understand your description correctly. The wording did change slightly in the 2020 edition, but the application is the same.

Thank you! The reason I'm asking is because according to NEC 2017 wording, per my understanding, the 10kAIC panel fed motors would not be included, but per the new NEC 2020, it somewhat sounds like they would be.

 

[mayanees]

Yeah you're right that wording is different. I think they corrected a mistake in the wording because I believe the intent is that it's on the load side of the distribution breaker. So in your case, now you need a fault current calculation for the devices in that panel!

 

[curious101]

Yeah you're right that wording is different. I think they corrected a mistake in the wording because I believe the intent is that it's on the load side of the distribution breaker. So in your case, now you need a fault current calculation for the devices in that panel!

Thanks!

 

[hhsting]

Thank you! The reason I'm asking is because according to NEC 2017 wording, per my understanding, the 10kAIC panel fed motors would not be included, but per the new NEC 2020, it somewhat sounds like they would be.

Wording in NEC 2020 and NEC 2017 means same thing! In either edition you need to take into account sum of all motor loads in 10kAIC panel, MDP etc

Hello,
Question regarding the above listed code section. I have a case where in the main distribution panel (MDP), a 225A/3P circuit breaker (feeding a 10kAIC MLO panel which has motors on it) is series rated with the upstream 65kAIC, 800A service disconnect with overcurrent protection. Roof top units are fed off the MDP and some condensing units off some panels fed from the MDP. Does the sum of the motor full load Amps - per the above mentioned NEC section - include all the motors in the 10kAIC panel and the roof top units and the condensing unit motors too?
I have read some posts on this code section, but it seems to me that NEC 2020 has different wording than the previous NEC versions, so it would be nice to get clarification.
Please let me know if you have any questions.
Thanks, and have a great day!

Yes it includes all the motor loads sum. You cannot use series rating should sum exceed 1%. You need to provide short circuit fault current calculation with motor load contribution. Breakers need to be fully rated based on that calculation

 

[curious101]

Wording in NEC 2020 and NEC 2017 means same thing! In either edition you need to take into account sum of all motor loads in 10kAIC panel, MDP etc





Yes it includes all the motor loads sum. You cannot use series rating should sum exceed 1%. You need to provide short circuit fault current calculation with motor load contribution. Breakers need to be fully rated based on that calculation

Thank you so much! Have a great day!