24VDC beside 14000VAC


Thread Starter


Because of tray work, it would be easier to run my PLC 24VDC signals on the same tray that carries 14kV (~2700Amps).

Is there a code reference that I can look? or a web page? I could not find it in the Canadian Electrical code book.

Isn't there a rule that parallel is OK but perpendicular is not?

Thanks for your help

Bob Peterson

NEC requires that all conductors in a cable tray or raceway have the insulation ratings higher then the maximum voltage in the tray or raceway.
You would need to use cable suitable for 14kV for your 24VDC if you chose to do this. I think it also prohibits you specifically from doing what you want to do here. An extremely dangerous condition could result if the insulation on one of your 14kV lines was damaged and you had low voltage wiring in it. The insulation could (and probaby would) fail on your low voltage wiring
potentially causing a VERY high voltage spike into your control system.

The NEC (NFPA 70) only covers low voltage equipment (low voltage being upto 600 V). Other codes cover equipment above 600 V. They probably prohibit what you want to do.

I think you need to consult with someone competant in the area of electrical design.

Bob Peterson

Jeremy Pollard

Normally anything over 300 V you need to keep unsheilded cable 3feet min. 1 foot from 120V -300V. I wold not run it in the same tray but use shielded cable of some sort and hang it 3 ft below the tray

Normally If I remember correctly, when you cross lines of different voltages, you should do it at right angles due to inductance. There will be a lot of inductive field surrounding the 14KV line. Wise to respect it.

Cheers from:

Jeremy Pollard, CET
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Michael Griffin

Mr. Peterson is quite correct here, and the same consideration applies under the Canadian Electrical Code. All conductors within a panel or raceway must be rated for the highest voltage present unless they are physically separated by an insulating barrier which will prevent them from coming in contact.

I would say that your 24VDC control wires need to be as far away from the 14000V lines as possible, and definitely not in the same cable tray or even close to the cable tray.

I think that you will also find that it will not be "easy" to run them together, even leaving the insulation problem aside. I don't believe that an ordinary industrial electrician is licensed to work near 14000V (and most would refuse to go near it), so you would have to get high voltage specialists if you have control cable problems. Furthermore, I suspect that the only thing your control system would see in the 24VDC wires would be induced voltage from the 14000 volt 2700 amp lines.

Michael Griffin
London, Ont. Canada

Curt Wuollet

Even if it's legal, it sounds like a bad idea on strictly technical grounds. Especially if the HV isn't steady state. Even if you shield to prevent
electrostatic (potential) coupling, At 2700 amps you will have significant magnetic coupling which is difficult to shield. I'd prefer not to get close enough to drop it in the same tray. That's an enormous amount of power. Very difficult to keep the physical relationship constant enough to even predict results. Consider what .1% coupling would do.


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I don't want to sound insulting, but, if you have to ask this question, PLEASE !!!
Do not get near these High Voltage cables for any reason.
Leave alone the HV, At 2700 amps the amount of magnetic field disturbing the PLC 24 signal is for sure. And with HV the chances are any leakage from the HV line will penetrate your control system.
One small creep and you loose the PLC and if you were working we loose you also. Please do not do it.
It is esy and cheaper to run HV and 24 v dc trays separtely. Also make sure any groung fault on the HV will not damage your PLC. Try to use isolators to all signals that go outside the panel if the HV termination is also nearby,