MIxed voltages in a single conduit

We have an application where, due to severe space constraints, we are going to have to mix voltages in a single 32mm conduit. The cables are:

1. 24Vdc, 4 wire stepper motor supply (limited to 4A by controller)

2. 110Vac drive motor supply (rated at 19A max)

3. Screened 24Vdc control cabling (for limit switch)

I understand this is far from ideal, but is it acceptable?

Will twisting the stepper motor supply help (i.e. have the A & B poles as two separate pairs).

All wiring will have same rated insulation.

Again, I understand this is not optimal, but are there any insurmountable reasons this cannot be done?

  • It is not best practice, and I;d avoid if possible but, so long as the cable is all rated for the 110V, and the risk of some catastrophic failure where the 100V ends up on one of the other circuits can be managed (either by fuses blowing or gear blowing up in a contained nonlethal sort of  way is usually OK) it should be manageable. After all if all the cables were part of the wiring loom inside one machine you would not blink. So much for the safety side.
    There may be problems if say motor surges cause the thing reading the limit switch circuit to think it has operated when it hasn't or similar, but that is an EMC thing that will depend how far they run parallel and how rounded are the driving waveforms.- how much of that is under your control to add filters and surge suppression components if you find they are needed ?
    Twisted or better still screened cables are your friend for this and a carefully thought out approach to how the screens are connected.

  • Cheers,

    The limit cabling is fully screened, twisted pair so hopefully will be OK.

    I'm 100% with you that it's not "best practice" but space and time are equally in short supply so I'm just trying to do the best with what we have.

    I'll be grounding the screen on an instrument ground at the control panel end and leaving it disconnected at the limit end.

    Many thanks for your help