# Motors Locked Rotor Current - NEC Question regarding Tables 430.251 and Table 430.7(B)



## akyip (Aug 2, 2020)

Hey guys,

I have a question regarding motor locked-rotor currents from the NEC. This comes from several practice exam questions regarding calculating max locked-rotor current of motors.

Table 430.7(B) is for locked-rotor indicating code letters, and applies to all motor design code letters.

Table 430.251(B) is for locked-rotor currents specifically for 3-phase or poly-phase Design B, C, and D motors.

I understand that for most motors (not Design B, C, and D), you can find the max locked-rotor power from Table 430.7(B) and then use basic power equations to solve for max locked-rotor current.

But my question specifically for Designs B, C, and D 3-phase motors is: for finding max locked-rotor current do we just simply use Table 430.251(B) to find the max locked rotor current? Or do we calculate which locked-rotor current is higher between Table 430.7(B) and Table 430.251(B)?

Thanks for any input on this!


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## BebeshKing PE (Aug 2, 2020)

akyip said:


> Hey guys,
> 
> I have a question regarding motor locked-rotor currents from the NEC. This comes from several practice exam questions regarding calculating max locked-rotor current of motors.
> 
> ...


Table 430.251(B) is the maximum LRC for the selection of* Disconnecting means and controllers.*

Hope that will enlighten you.


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## Zach Stone P.E. (Aug 3, 2020)

BebeshKing said:


> Table 430.251(B) is the maximum LRC for the selection of* Disconnecting means and controllers.*
> 
> Hope that will enlighten you.


Bingo.


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## akyip (Aug 3, 2020)

Alright, thanks!


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