# Conductor Ampacity using Motors



## EEVA PE (Sep 9, 2011)

According to the NEC 430.6 (A) (1), when will I use Nameplate Full Load Current value instead of Table 430.250 value? If I do not meet the speed or torque requirements in NEC 430.6 (A)(1) and my name plate current is less than table value, I use Table Value. If name plate current is greater than table value, I use nameplate value. I see in the NEC 430.6 (A)(1) where to use table value, but do not see it written where to use name plate value when the name plate full load current is greater than table value. I see it for overload protection.


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## BamaBino (Sep 9, 2011)

EEVA said:


> According to the NEC 430.6 (A) (1), when will I use Nameplate Full Load Current value instead of Table 430.250 value? If I do not meet the speed or torque requirements in NEC 430.6 (A)(1) and my name plate current is less than table value, I use Table Value. If name plate current is greater than table value, I use nameplate value. I see in the NEC 430.6 (A)(1) where to use table value, but do not see it written where to use name plate value when the name plate full load current is greater than table value. I see it for overload protection.


This got discussed here showtopic=13766 regarding Sample Problem 510.

I don't my study material with me at the moment but I believe this summarizes it:

according to 430.6(A)(1),tables 430.247 to 430.250 are used for breakers, fuses and conductors only, and not for overloads. Per 430.32(A)(1), overloads are sized based on manufacturer nameplate and not the NEC table.


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## EEVA PE (Sep 10, 2011)

BamaBino said:


> EEVA said:
> 
> 
> > According to the NEC 430.6 (A) (1), when will I use Nameplate Full Load Current value instead of Table 430.250 value? If I do not meet the speed or torque requirements in NEC 430.6 (A)(1) and my name plate current is less than table value, I use Table Value. If name plate current is greater than table value, I use nameplate value. I see in the NEC 430.6 (A)(1) where to use table value, but do not see it written where to use name plate value when the name plate full load current is greater than table value. I see it for overload protection.
> ...


The reason why I ask is because in the NEC Annex D-8, the question asks about the conductor ampacity of "two" 30-HP motors. When you look at the solution, it treats one answer using the nameplate and the other using the table.


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## Flyer_PE (Sep 10, 2011)

I'm no code expert, but I think the difference lies in what you are sizing. If you are setting up cable size and protection, the full load currents given in the tables are used since the table values are intentionally conservative. If you are selecting protection for the motor itself, use the nameplate since the higher current values found in the tables will be non-conservative in this application.


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