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Motor O.C. protection

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thefuse

Electrical
Joined
Oct 13, 2006
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Location
US
NEC Table 430-52 states the maximum O.C. protection values allowed for motor protection.
Recently I received from our mechanical engineer a cut-sheet from a mechanical equipment manufacturer that based their maximum OC protection for fuses on a value using 225% of the largest motor of this multi-motor package. Of course this was not the same value I had calculated at 175%.
How can the manufacturer not comply with the NEC in this manner?
 
Hi there!! well, if that's the case, check NEC 440.22. This section talks about AC equipment (I assume this is AC equipment, since you mention a "mechanical engineer" involved in this issue). The manufacturer might be trying to make sure the motor starting current is sufficient without tripping the breaker.
 
Note exception 2(b) under Table 430.52.
 
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