# Motor Load protection



## Bulldog1 (Oct 21, 2011)

CelticElect said:


> I had some chiller loop pumps installed and noticed that the pumps name plates read 29.9 amps (34 Amps FLC according to Table 430.250) for a 25 HP 480v motor. If you take 125% of 34 amps you will come out with 42.5 amps for continuous use for Overload Protection. The electricians installed a 70 amp breaker in the load center. Is that the correct protection? FYI: There is one backup pump for each loop. So a set of pumps for each.



If you are asking if the feeder overcurrent protection is sized correctly you take the largest breaker and add the FLA of the other motors to it. 

For example if the largest breaker was a 40 amp breaker and you had 2 additional motore with a FLA of 30 amps then it's 40+ 30 + 30 = 100 amp breaker for OCP.


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## CelticElect (Nov 17, 2011)

Bulldog1 said:


> If you are asking if the feeder overcurrent protection is sized correctly you take the largest breaker and add the FLA of the other motors to it.
> 
> For example if the largest breaker was a 40 amp breaker and you had 2 additional motore with a FLA of 30 amps then it's 40+ 30 + 30 = 100 amp breaker for OCP.


Each pump is individually fed. There aren't any other loads attached to these pumps. We are feeding one 25HP 480v pump at 70 amps. When I think it should be fed at 45 amps. Is the 70 amp breaker wrong?


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## Bulldog1 (Oct 21, 2011)

CelticElect said:


> Each pump is individually fed. There aren't any other loads attached to these pumps. We are feeding one 25HP 480v pump at 70 amps. When I think it should be fed at 45 amps. Is the 70 amp breaker wrong?



Look in 430 I don't have a code book with me. You can go up to either 175% or 250% for OCPD I believe. I believe the article says 250%. If so then a 70 amp breaker is the correct size.


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## CelticElect (Nov 17, 2011)

Bulldog1 said:


> Look in 430 I don't have a code book with me. You can go up to either 175% or 250% for OCPD I believe. I believe the article says 250%. If so then a 70 amp breaker is the correct size.


Found it! They are using "varying duty" from Table 430.22(E) which is 200% of FLC. Vetting duty is found in Artical 100 under "duty" for it's definition.

Thanks


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## Bulldog1 (Oct 21, 2011)

CelticElect said:


> Found it! They are using "varying duty" from Table 430.22(E) which is 200% of FLC. Vetting duty is found in Artical 100 under "duty" for it's definition.
> 
> Thanks



No problem. I can never remember those %. Glad I could help.


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## varmit (Apr 19, 2009)

Unless the breaker is a very expensive class, 70 amps is about right to handle the inrush of a 25 HP motor. If using time delay fuses, 45 or 50 amp would usually be correct.


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## don_resqcapt19 (Jul 18, 2010)

The breaker in a motor circuit only provides the ground fault and short circuit protection. The wire is required to be sized at 125% of the current as shown in tables 430.247 through 430.250. A thermal magnetic breaker used for the short circuit and ground fault protection is permitted to be sized at 250% of the current shown in the tables. The motor overload device must be sized based on the motor nameplate current and not the current shown in the tables.


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