Adjustable Speed Drive

[infinity]

Someone asked me today about sizing the conductors and OCPD for a 480 volt VFD with a nameplate rating of 59 amps with a 20 HP motor. I commented that the conductors to the VFD are sized at 125% of the VFD rated current but got stumped on the OCPD size.

 

[Rockyd]

Section X starts at 430.120.

 

[Jesse7623]

All the frequency drives I have installed have built in OCPD.So you up size 125% for both the conductors and the fuses.

 

[weressl]

Someone asked me today about sizing the conductors and OCPD for a 480 volt VFD with a nameplate rating of 59 amps with a 20 HP motor. I commented that the conductors to the VFD are sized at 125% of the VFD rated current but got stumped on the OCPD size.

You really need to look at the ASD's installation instructions. Depends on the duty they are able to perform they are capable to operate under overloaded conmditions for pre-set periods of time. Best thing is to follow the manufacturer's minumum OCPD size and size the cable accrodingly.

 

[infinity]

I think that the issue is that the engineer sized the feeder to the drive based on the motor FLA and not the ampacity of the drive. The other question is the conductors are sized at 125% of the rating of the drive so would the OCPD feeding the drive be sized at 125% or would it be sized at 175% like a normal motor starter?