VFD Reactor and Fusing 3

[itsmoked]

If I'm stuck using a 20HP VFD for a 15hp motor can I use the appropriate 15hp reactor and fuse the drive with the appropriate fuses for 15hp or do I have to use the reactor and fuses for the rated drive?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

The code will require any components on the supply side of the drive to sized according to the nameplate specs of the drive.
Will it work?
Probably.
Verify that the 15 Amp components will support the initial charging of the capacitors.
If the reactor is on the output, it may possibly be sized according to the motor nameplate.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

That's what I thought. Dang. And thanks!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

Specifically (because Bill is Canadian) NEC article 430.122 requires the CONDUCTORS to be sized at 125% of the rated INPUT current of the VFD But the only thing actually dictating the fuse sizing is the listing info for the drive, and they will typically only give you the MAXIMUM fuse size (and type). You can use smaller if you like, it’s just your risk.

As to sizing the reactor, 110.3 calls for devices to be used as per the mfr instructions and that they’ve suitable for the use. One could argue your proposal either way.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[itsmoked]

Gotcha. It's all in a free standing electrical enclosure in the middle of a half acre of concrete, it could all slag down and not be a hazard to anything. It's painful to spend the money on something that will never be changed. I'm dithering on it all. I suspect the drive even has a charging circuit so the reactor and fuses won't see 20hp consumption ever. Of course the drive will have the FLA programmed in so it won't ever suck more than 15hp. Groan.

Thanks Jeff.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[LionelHutz]

Well, if you size the reactor for 20hp but use on 15hp you will reduce it's effect a bit. I would size to the motor. Done it and seen it done many times without being questioned yet.

 

[jraef]

I suspect the drive even has a charging circuit so the reactor and fuses won't see 20hp consumption ever. Of course the drive will have the FLA programmed in so it won't ever suck more than 15hp.

Correct on both counts. Pre-charge circuit prevents excess capacitor charging current, programming the VFD to what the actual nameplate data shows will mean the VFD will not allow more than the maximum the motor can handle.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[itsmoked]

LH; That's what I was thinking. So then I was contemplating a 5% instead of 3% reactor but then they cost 50% more! I'm going with the 15hp setup.
Thanks much all.

Keith Cress
kcress -

http://www.flaminsystems.com