Question on VFD sizing

[thewellguy]

I want to use a vfd to control a pump. The question that I have is that I have a 230 1 phase input and will be using a 230 3 phase output. The ASC550 ABB drive that I will be using calls for a 50% derate on the drive. The question is what size fusing is required, full load of the drive that is derated by 50% or can I go smaller? Thanks for the help in advance.

 

[CJCPE]

I think you need to size the input fuses, conductors, branch circuit protection etc. per code based on the drive's nameplate current. The only reduction you get is that for single phase input, you only have 2 fuses and 2 conductors etc. instead of the 3 you would have for 3-phase.

 

[DickDV]

CJCPE is correct as to input fuse sizing.

 

[jraef]

Usually, fuses on a VFD circuit are recommended just to protect the VFD components from short circuit current, unless they are also the branch Short Circuit Protective Device (SCPD) as well. The SCPD needs to be sized for the conductors TO the drive, which should be sized for the VFD max. amps. The conductors FROM the drive to the motor will be protected by the VFD and can be sized for the motor load, as long as their rating still falls within the allowable exceptions in NEC 430.52. In other words, fuse to protect the drive, size conductors accordingly. Don't skimp.



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[LionelHutz]

The single phase input current will be higher than the motor current, typically about 1.73 times higher. VA in has to equal VA out. 3-phase VA is volts x amps x 1.73. 1-phase VA is volts x amps. So, you need to size the incoming based on this. So basically, size to the input rating of the drive.