Cables in Conduit in Class I Div I

[CLASS_ONE]

Hello,

we are building a machine for a class I div I location. There is a cabinet witch is purged and pressurized (Type-X) inside this location and a second cabinet outside.

In the purged cabinet there are the most controlling systems (PC, Oscilloscope, ...) with a window for the monitor and a class I div I keyboard outside. I want to use a bus system (Profibus) to control the external cabinet outside. This Profibus cable is shielded and contain two conductors for the data.

I have to use conduits with sealings to go from inside the hazardous area to outside, that's clear. I have read the NEC (2005) in special 501.15(D)(2), and for me it's not clear, do this apply or not. The entrance is inside the purged cabinet and the exit is outside the hazardous area and the cable is inside the canduit with sealings, but the cable isn't classified gas/vaportight.

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a second point: from the purged cabinet i have some cables witch are going to the machine. This machine is located in the hazardous location. I use there classified stuff, but i have some shielded cables, thermocouple wires, ... not allways single conductors. How should this stuff be connected to have no problems with the NEC?

Can someone give me some hints.

I'm looking forward to your replies. Thanks a lot in advance.

 

[rbalex]

I’m not a graphic artist so please accept the image I put together as "diagrammatic"

View attachment 1160

On the left is the “basic” rule where one sealing “mass” covers both outer jacket and individual conductors. The Exception is on the right. We should distinguish between “listed” and “approved” here. The conduit seal must specifically be listed per 501.15(C)(1). In the Exception, the cable seal must be "approved." The distinction is that there are no specifically “listed” cable seals for this particular application so the AHJ must make a judgment call. Personally, I recommend a mastic filled shrink-on kit. Several manufacturers make them.

It should also be clarified that once the cable is sealed at the terminations as also required by 501.15(D)(1), the Exception then permits the cable to be treated as a single conductor throughout the rest of its run.

As for the shielded cables, the Exception covers them too. Nothing is required that may damage their integrity.

 

[CLASS_ONE]

Hello Bob,

thank you for your reply. You've created a very good drawing - thanks a lot.


I have additional questions for this item.
1) What do you mean with "AHJ"? I don't know this abbreviation.
2) In 501.15(D)(1) there is a note for a MC-HL cable, i don't have one of this. I use standard UL listed/approved cables. Do the exception only refer to the MC-HL cable types or to all (listed, approved) cables?

Regards

 

[CLASS_ONE]

Hello again,

first think - then ask ...

AHJ stands for "Authority Having Jurisdiction". First question is solved, but the second is still active... ;-)

 

[rbalex]

I haven?t quite liked the wording of 501.15(D)(1) since MC-HL was introduced, but I have never been able to get Code Making Panel 14 (CMP14) to change it. The first two sentences, ?Cable shall be sealed at all terminations.? and ?The sealing fitting shall comply with 501.15(C)? are general. They have been part of the basic rule a long time.

Part of the third sentence is also general and been around for a long time: ??after removing the jacket and any other covering so that the sealing compound surrounds each individual insulated conductor in such a manner as to minimize the passage of gases and vapors.?

The introduction of MC-HL as a Division 1 wiring method happened in 1996. I was the original proposer through API. The proposal got wordsmithed both in the API working group and the CMP14. Truthfully, I was so pleased with myself I didn?t quite realize it didn?t quite say what I intended primarily because we were focused on cable-only wiring methods at the time.

In any case, the 501.15(D)(1) Exception is also general and the concept is similarly reflected in the 501.15(D)(2) Exception.