# Cable and BCP sizing for VFDs and Motors



## HARRY304E (Sep 15, 2010)

sjperreault said:


> Does anyone know if NEC allows cable and branch circuit protection to be sized for motor amps instead of VFD amps? Example - motor is 414 amps, but had to use 675 amp drive because of availability. Can cable and branch ciruit protection be sized based on 414 amp motor? If so, what specific article of NEC would allow this?




ARTICLE 430— MOTORS, MOTOR CIRCUITS, AND CONTROLLERS


Welcome to the forum..:thumbup:


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## John Valdes (May 17, 2007)

Motor conductor size is calculated at 125% of the nameplate FLA. The drive has nothing to do with this.


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## don_resqcapt19 (Jul 18, 2010)

The branch circuit that supplies the VFD has to be sized at 125% of the VFD input amps. 430.122 I am not aware of a code section that permits a smaller supply conductor even where the VFD is oversized for the motor.


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## John Valdes (May 17, 2007)

don_resqcapt19 said:


> The branch circuit that supplies the VFD has to be sized at 125% of the VFD input amps. 430.122 I am not aware of a code section that permits a smaller supply conductor even where the VFD is oversized for the motor.


I agree. But he only asked about the motor conductors? At least thats what I thought. Glad you were thinking. :thumbsup:


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## sjperreault (Mar 22, 2011)

Thanks Harry, John, and Don. I was actually speaking of both input and output conductors for the VFD.

Someone told me that Article 310 provides an alternate way to size conductors "based on calculation," that might allow what I'm asking. Any truth to this possibility?


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## don_resqcapt19 (Jul 18, 2010)

Take a look at 310.15(C).


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## mei163 (May 9, 2011)

don_resqcapt19 said:


> The branch circuit that supplies the VFD has to be sized at 125% of the VFD input amps. 430.122 I am not aware of a code section that permits a smaller supply conductor even where the VFD is oversized for the motor.


I agree. should be sized at 125% of the VFD input amps.


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