AC and DC Drive Conductors in the Same Conduit?

[JimCook]

One of our plants has DC motor conductors for several DC drives run in the same conduit. They want to replace one of the DC motors with a 3-phase induction motor and run the AC drive conductors in the same conduit as the DC motor conductors. I think this is a very bad idea but there is no Code restriction against it. It seems to me that the AC drive would be inducing weird AC currents in the DC conductors and that could adversely impact the DC motors. Comments?

 

[PeterKsiazek]

This is a bad idea, and not something I would allow. Especially if a VFD is used as there will be all sorts of crazy harmonics.

 

[itsmoked]

It would be better to run them separately but unless you have some sadly misplaced control wiring in the same conduit you probably can get away with it.

If the DC drives are PWM controlled now, more hash in the pipe isn't going to cause an issue.

Remember that all the wires in a conduit have to have at least the insulation needed for highest voltage in the conduit.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[rbulsara]

Code requirements are only for safety against fire and personal injury. Code does not care if the system works or not. It is designer and contractor's responsiblity to make the system work per the contract or intention.

 

[JimCook]

I advised against it for the reasons all of you mention. I never recommend running motor leads from multiple drives, DC or AC, in the same pipe. But that's the way they originally installed the DC drives and it has worked for fifteen years or so without incident. But parts for these drives are getting hard to come by and they want to change these over, one by one, to AC drives.

Thanks for your comments!