Does Intrinsically safe circuit need to be run in cable tray or conduit?

[molebleeze]

We have been using shielded ITC blue cable for intrinsically safe circuit.
It is running in cable tray for major long run.
However, when jumping off the cable tray, do those IS cables need to be run in conduit to get to the IS instruments? Is free-run cable allowed per code?

Thanks...

 

[robertjo24]

I cannot speak to the code, as I don’t know it verbatim, nor for your area… But, the generally accepted proper way to run cabling from a cable tray to instrumentation would be to install the cable in conduit. I don’t think anyone allows direct burring of cable, or a dangling free run, particularly in an industrial environment. Everyone has their own internal standard as to what type of conduit it should be, and if buried if it should be encased in concrete (and if so, what color). At a minimum, it should be galvanized rigid conduit, sized sufficiently to allow no more than 40% fill. For one cable, I would run a ¾”.

From the instrument to the conduit, there would be an approved flexible coupling. At the conduit, the coupling would connect through a typical junction bot or fitting (LB), then through a seal, then to the conduit.

At the cable tray end, the conduit would extend to the cable tray, positioned sufficiently to support the cable transition from the conduit to the tray.

The idea is to protect from any hazardous fluids (gasses or liquids) traveling from a classified (hazardous) area to an unclassified area through the conduit.

 

[controlnovice]

Check out NEC70, Section 504.20:

If you already have it in Cable Tray with other cables, it needs to be separated by 50mm (2in) (or a partition), unless they are in a grounded metal sheath..then they can be in same tray.

When leaving the tray, follow Section 300 for protecting the wire with conduit. I think your type of cable will require a conduit or channel for protection. When using either, follow the labeling guidelines in Section 504 (blue labels on the conduit)...



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This is normally the space where people post something insightful.

 

[molebleeze]

@robertjo24
@controlnovice

Does the last mile run to the instrument have to be in rigid metal conduit? I am thinking using EMT or even strut to reduce the cost. Will that be acceptable?

 

[itsmoked]

If it's intrinsically safe I don't believe it needs to be rigid conduit. That's more the purvey of Exp wiring. I don't think you need conduit at all. I believe you could staple cable to wall if you wanted.

What you do have to do is keep the intrinsically safe cabling safely isolated from any wires carrying any non-protected circuits. If that requires conduit then that's what's needed. Secondly, you need to always keep the incendiary space physically isolated from the safe space. Usually this is done with conduit that separates the two spaces being filled at some point with a hardening chemical filling.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[InstEngr]

When used with mechanical seals on each end, conduit does allow electrical circuits to meet the area classification. However, the second purpose of conduit is merely for physical protection. Obviously with an IS circuit, a conduit with EYS type seal is not required but the cables may still need physical protection. With an IS circuit, when leaving a cable tray, I either route the wires in conduit or in a metal raceway to the final instrument or JB. If going to a JB, you may want to use a conduit regardless, to make entry into the JB simpler.

If you do jump from a cable tray to conduit, make sure the end of the conduit is not sharp or it will wear through the cable. They make plastic end caps that prevent the cable from rubbing against the metal.