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Circuit Breaker Code Question

Question asked by taylor.hunter on Jul 26, 2018
Latest reply on Dec 15, 2018 by opes

Hello all, 

 

We recently had to upgrade all of our products to run with Design B energy-efficient motors. After a few weeks we started getting customer complaints of nuisance tripping. After investigating we discovered the new motors have much higher inrush ratings. 

 

For example: Motor FLA was 13.1, with inrush spikes up to 194 A. Our thermal magnetic breaker was rated 10...16 A FLA with instantaneous trip of 208 A (+/-20%) As a quick fix we simply installed the next size up breaker, 13...20 A with instantaneous of 260 A. This seems to have solved the issue.

 

However, we are concerned about NEC 430.52. In the table it states for Design B energy-efficient motors, breakers should not exceed 1100% of FLA for instantaneous trip. 430.52 (C) (3) Exception 1 states that if breaker settings are not sufficient for Design B motor starting current, you shall be permitted to use no more than 1700% of FLA instead. So, it seems the max instantaneous trip rating we can use for this motor is (13.1x17) 222.7 A.

 

Since our max inrush is 194 A, and the next highest instantaneous rating for our breaker model is 260 A.. would we fall into this exception? 430.52 (C) (1): "Exception No. 1: Where the values for branch-circuit short-circuit and ground-fault protective devices determined by Table 430.52 do not correspond to the standard sizes or ratings of fuses, nonadjustable circuit breakers, thermal protective devices, or possible settings of adjustable circuit breakers, a higher size, rating, or possible setting that does not exceed the next higher standard ampere rating shall be permitted."

 

Meaning we could use the 260 A breaker and still be within code?

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