Can you run multiple 3-phase motor power circuits in the same multiconductor cable?

[bdn2004]

We have 4 small motors located about 100' away from their motor starters. They are fans on a heat exchanger. The conduit to them runs outside underground to a junction box and into cable tray inside to the control panel. We have a roll of 12/C #10 and we can include a ground wire in the conduit...that seems like it would work ok....just never seen such an installation. I've always seen cables one cable per one motor. Is this a bad design idea?

 

[dpc]

It's not an NEC violation. But the ampacity of the #10 must be de-rated.

 

[rcw retired EE]

If one motor circuit wire fails, all four motors will have to shut down to make the replacement. If that is not a problem, using a single 12/C- #10awg cable might work. Derate the wire correctly for ambient temperature and more than 3 current carrying wires in a conduit.

 

[jraef]

Caveat: do NOT do this if they are on VFDs, or ever will be some day!

"Will work for (the memory of) salami"

 

[waross]

Not allowed under the Canadian Electrical Code:
4-040 Uses of portable power cable (see Appendix B)
......
(3) Portable power cable shall not be used
(a) as a substitute for the fixed wiring of structures and shall not be
(i) permanently secured to any structural member;
(ii) run through holes in walls, ceilings, or floors of permanent structures; or
(iii) run through doorways, windows, or similar openings of permanent structures; or
Also, under the CEC, the cable must be listed in table 19 as suitable for use in raceways.
There may be similar provisions in the NEC.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Padlock01]

Hi Bdn2400
I would say that its not the norm to do this in RSA, are you on a "tight budget" the most drives I have put in one cable is two and they were 525volt vibrating motors on the same vibrator, anyway just make sure that the four drives have seperate thermal overloads.

 

[bdn2004]

Waross,

This isn't portable or flexible cords, it's 600V tray rated cable to be permanently installed. We have many partial rolls of speciality cables left over from at least ten years of projects we would like to put to use if we can. Actually I made a mistake on this post...it's 7/C #10 we have, and now I'm planning to use 2 runs of it. 2 motors will run at the same time. One set of motors is redundant.

Saving $500 dollars on wire might not sound like much, but after a Contractor charges his markup, charges us shipping and handling it's easily a $1000 savings that can be shown on our project. Every bit helps. We're always on a tight budget...

 

[waross]

I don't see a real problem. Conductors approved for raceways are strong enough to withstand pulling in without damage. I am sure tray cable is strong enough to be pulled. But not all inspectors spent much time in the real world before becoming the AHJ. I have run into inspectors who would demand to see the cable listed as suitable for installation in raceways.
I would consider using the cable as you intend, but I would run it by the AHJ first. Spending the $1000 and the labor to remove and install doesn't look good on a resume.
Watch your conduit fill for single cables and two cables in a raceway. Under our code the percentage fill is different for one, two or three cables in a raceway.

Bill
--------------------
"Why not the best?"
Jimmy Carter