ECN Forum Forums Code Related Discussion NEC & other Code issues VFD Questions

I am having some VFD issues, looking for advice. Can the line and load conductors from a VFD be in the same raceway and can the loads from multiple VFD's be in the same raceway. I have reviewed multiple VFD manufacturers installation manuals with no good direction.

oldsparky,

I have installed several VFDs with the line & load conductors in the same raceway, and they worked fine for years.

I did however have a problem with voltages induced in a VFD with a 5 volt control circuit that shared a raceway with the load conductors. The VFD load conductors were inducing about 8 volts in the control wires and if I let go of the stop button during the ramp-to-stop period, the motor started up again.

For various reasons, we couldn't run a separate contol conduit, so we actually bought a new drive with a 10 volt control circuit and the problem went away.

That all being said, I would call your suppliers VFD man. He should be able to advise you.

BTW,

Are they Allen Bradley?

Seperate line and load conductors. Seperate signaling (control) circuits. Yes, individul conduits. Install a line reactor for each control (VFD). If motor is more than 100' away from drive install a load reactor. Inductive currents from the drive output will dirty up the input conductors causing nuisance tripping of the drive. The only place where the conductors should meet is in the control panel. Keeping control, line and load away from each other. You can use one breaker and a terminal block for several drives. But you should use seperate line reactors.

Note: Some VFD's have the reactor built in.
Try www.baldor.com and look under brochures or manuals. You can get anything you want there in PDF format.
Check www.transcoil.com. Or search Trans Coil Inc. for line and load reators and further information.