Instrument Cable in an Electrical Transit

Is it possible to put an instrument cable through an electrical cable transit? Given the electrical cable is only rated below 1kV, is this procedure acceptable by NEC?

An instrument cable, by definition, is also an electrical cable.

The concept you're most likely referring to is signal level separation. It's NOT advisable to mix instrument cables (typically less than 50 or 25 VDC) with cables above these levels--especially if the higher voltage cables have AC in them and if the currents are high and change frequently (motors starting and stopping; loads suddenly increasing or decreasing).

Properly shielded instrument cable has been run for short distances in "cable transits" (what's a cable transit? I know about cable conduits; cable trays; cable vaults. But I've never heard of a cable transit? Is it something in commercial buildings in walls?). Running an instrument cable a "long" distance with other higher level electrical cables is not recommended.

Most instrument manufacturers will have some kind of specification about how the instrument cables used to connect to their equipment should be separated from other electrical cables. The worst mixing would be in a metal conduit (pipe), slightly less worse is cable trays (metal cable trays, often with sheet metal covers).

But, the big thing to avoid is mixing instrument cables with other cables that have high currents--especially AC currents--in them. And, if the currents change abruptly that's also bad.

The problem with running instrument cables with higher voltage electrical cables is that electrical noise can be induced in the instrument cables, and NO ONE like to hear there's electrical noise in the system. Ever! It's just not fun to troubleshoot, or to fix.

Many instrument cables are run short distances under false floors in control rooms for short distances (a few feet, or sometimes a little longer), and inside control panels also. But, if the signal in the instrument cable is very low level (say, 12 VDC, or 24 VDC @ 4-20 mA) or similar) and there are high-voltage AC cables nearby it's always best to provide as much separation as possible--especially in metal conduits or cable trays.

I don't think NEC has any "rules" about this, but, again, most instrument manufacturers have their recommendations.

Best of luck! (I'd still like to know what a cable transit it, what it's made of, and how long of a distance you are talking about, and how much physical separation you could provide between the instrument cable and the other electrical cables.)
I agree with CSA its not a good idea. However, instrument cables are often run on an electrical tray with a metal barrier in between. If the cables are just lighting or low power motors, it's probably ok.

If you must transmit a number of instrument signals along a high Voltage cable tray, try looking for a fiber optic transceiver.

Heinz Janiec

I agree with the above statements, but even for short cables you should use shielded cable. Maybe you can use even none preconfectioned Ethernet cable like CAT 5 or 6 and always ground the shield at the mist sensitive side of the used devices.