VFD/pump installation

[chuckd70]

Hello,

I am preparing to install a 20 HP pump with a 480VAC VFD, and am getting a little bogged down in interpreting the NEC. Since it is only be about 15 feet, and within sight of the panel that will be feeding it, I think I can get away without using a disconnect. Also, from the installation manual, it seems to me that the use of backup fuses are optional. The name plate says 35 Amps (but didn't say FLA or MOP), but the installation manual says the max recommended fuse size is 36A. It also appears to me that using a GFCI breaker is optional (and often causes problems with nuisance tripping).

So, my basic plan was to;

- install a 35A breaker in the panel (it is an old panel and GFI breakers are not available, so it will be a standard breaker)
- run a short section of conduit to a J-box
- run a 10' section of cord to the pump

Am I breaking any of the NEC rules using this approach?

Thanks for any insights

 

[Eddie702]

You have to size you conductors based on the required drive input, not the motor size. If the panel breaker is within 15' you should be ok even if the VFD does not have a disconnect.

Is this a submersible pump? Does the MFG call for a GFCI.

I don't know about using cord without knowing where the pump is installed

 

[chuckd70]

Thanks for the reply.

No, it isn't a submersible pump, and the MFG does not specifically say that the branch circuit be protected by a GFCI.

The cord will not be "subject to physical damage".

 

[tom baker]

Portable cord, such as SO, is not allowed to be used as a substitute for fixed wiring of a building.
is the pump motor inverter duty rated?
In my experience with VFDs, mfgs prefer fuses, but allows ckt breakers