Can innerduct be used to separate control cables from power and instrumentation cables? 1

[bdn2004]

I'm looking over a vendor's requirement to run a control cable to a piece of equipment. They are calling for the control cable to be separated physically from the power and instrumention cabling. It doesn't say by how much. I've seen innerduct used with fiber optic cabling inside conduits. Is another use of innerduct for the purpose I describe?

We have lots of cable tray installed that has a lot of spare space. We certainly don't want to have to spend the extra $$ to install cable tray barriers for one control cable. I thought of running the cable in an innerduct strapped to the inside bottom of the instrument tray...ok idea?

 

[dpc]

You don't provide the voltage levels involved, so it's hard to say. From an NEC perspective, mixing voltage levels up to 1000 V is not a code violations as long as all circuits are insulated for the highest voltage present. The exception would some type of power-limited control circuit. The vendor's concern is probably more related to electrical noise and interference rather than safety. Use of an innerduct (by itself) isn't going to reduce interference much.

 

[DRWeig]

As dpc said, if it's for electrical noise you need to consider shielding your cable or enclosing in metal innerduct.

The other good reason for separation is safety. You need to separate power-limited, class 2, or class 3 circuits from circuits under 600V by 50 mm. That's in the NEC, UL508, and UL508a.



Best to you,

Goober Dave

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[DRWeig]

I forgot to mention - solid plastic non-conductive innerduct may not fullfill the separation. The purpose is to prevent getting the high voltage into the low-voltage circuits, which could cause fire or personal safety downstream.

If you're looking at a private company's specification, you should ask them if they would accept it.

Best to you,

Goober Dave

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[bdn2004]

This is control wiring to a remote motor starter control panel from a vendor supplied PLC. The voltage is 48VDC.
We are using 12/C #14, 600V cable. There are 4 power loads (motors, heater) that require 480V that run to it too along the same route. It's all digital signals.
These motors are critical to the operation. The cable routes in new and existing cable trays between the first and second floor.

My question was about putting this into existing cable tray that is practically empty. Screwing in physical barriers would be costly. The new trays will have barriers in them.
If you've seen how cable tray ends up looking over the years - stuffed....it would make me feel better if this had a 2" innerduct or conduit around it to ensure the required separation.

 

[dpc]

You could run shielded cable and/or install in metal flex conduit in the tray. Or install C-L-X armored cable or similar.

 

[dbaird]

Have you looked at Exposed Run Cable? Cables that are listed ITC-ER or PLTC-ER are acceptable for use in hazardous locations as defined by NEC 725 and NEC 727. The ER stands for Exposed Run and indicates these cables may be run outside of cable tray or conduit as long as they are mechanically protected with struts, angles or channels every 1.8m (6’). To earn the ER designation cables must pass the UL1569 Crush and Impact Tests, which are the exact same tests used for metal clad cable, ensuring the cables strong.

David Baird
Sr Controls Designer
EET degree.

http://www.afctool.com