Motor Power and Control Wires in Common Conduit
Motor Power and Control Wires in Common Conduit
(OP)
I am presently designing a power and control wire routing via conduits from the associated LV MCC starter unit to the pump motor/local PB in the field. The power and control wires are routed into an adequately sized conduit where they split up once it reaches the pump/PB station through a GUAT conduit body.
I got a directive from my superior that the power and control wires should be routed in separate conduits. I asked him what is the basis and informed that it is an engineering practice.
I don’t see any reason why it should not be in common conduit since the power and control wires are 600VAC insulated and are coming from a common MCC starter.
Is this a code violation or not a good engineering practice?
I got a directive from my superior that the power and control wires should be routed in separate conduits. I asked him what is the basis and informed that it is an engineering practice.
I don’t see any reason why it should not be in common conduit since the power and control wires are 600VAC insulated and are coming from a common MCC starter.
Is this a code violation or not a good engineering practice?






RE: Motor Power and Control Wires in Common Conduit
RE: Motor Power and Control Wires in Common Conduit
Ausgen is right on the mark with the induced voltage on low level signals such as 24Vdc. Normally the low level signal cables are rated at 300V where your power cable is 600V making you segregate them. Some contractors run all 600V cable thinking they will not violate code and run into interference problems with the 4-20mA signal cables. So eventhough you may pass the code it is not good practice to mix power and signal cables.
I reccommend reading through NEC sections 310.15(B)(2)(a) and 392.11. Your supervisor may be trying to steer clear of the possibility of having to derate the power cables by Table 310.15(B)(2)(a) as well.
RE: Motor Power and Control Wires in Common Conduit
RE: Motor Power and Control Wires in Common Conduit
Any comments on this one?
RE: Motor Power and Control Wires in Common Conduit
I don't have a big issue with it in this case and this has been commonly done for decades. I would not say it is a bad engineering practice, at least at this point in time.
However, some organizations have strict rules about separating 120 V and 480 V circuits. So when in Rome....
Also, with increased concerns over electrical safety and arc-flash, some industries are moving away from 120 V ac control and going with 24 V dc for everything, including motor control circuits.
RE: Motor Power and Control Wires in Common Conduit
Gary B
RE: Motor Power and Control Wires in Common Conduit
RE: Motor Power and Control Wires in Common Conduit
RE: Motor Power and Control Wires in Common Conduit
RE: Motor Power and Control Wires in Common Conduit
RE: Motor Power and Control Wires in Common Conduit
But if no VFDs then you can mix like other said as long as the insulation is rated for the highest voltage.
If you have DC wires then these need to be seperated into seperate conduit, I do not believe you could get the proper result of a reliable control system if this is not the case.
I was involved in a project where we had bad electricians who ran the 480vac that had vfds with the 120vac.
Visiually we had estop indicating lights that would turn on when vfd motor would ramp and down. Also problems with radom firing of devices.
later we had to go in and put MOV on the io since we had noise bleed over from the 480vac vfd wiring.
some experiences can painful.
RE: Motor Power and Control Wires in Common Conduit
RE: Motor Power and Control Wires in Common Conduit
RE: Motor Power and Control Wires in Common Conduit
That is probably a NEC violation as to the size of the EGC. In general with power conductors sized #10 and smaller the rules in 250.122 will require that the EGC be the same size as the power conductors.
RE: Motor Power and Control Wires in Common Conduit
RE: Motor Power and Control Wires in Common Conduit
I missed the reference to the CEC. The NEC would require a #10 if the breaker is an thermal magnetic breaker, but permit a #14 EGC if the motor is fed from a listed combination starter that uses a magnetic only device for the ground fault and short circuit protection of the motor conductors.
RE: Motor Power and Control Wires in Common Conduit
After reading these posts I am wondering why specifically you do not want to run 120V controls with 480V power feeders controlled by a vfd? Can someone explain how a vfd would change the situation of running these together?
RE: Motor Power and Control Wires in Common Conduit
There's your answer.
Keith Cress
kcress - http://www.flaminsystems.com