Single Conductor Cable in Tray in Division 2 Locations

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osiris42

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Denver, CO
Long time listener, first time post-er.

An electrical contractor has raised a question regarding the suitability of single conductor (300kCMIL) in cable tray within a Class I, Division 2 location.

We initially ran the single conductor instead of multiconductor as the 3/C is often difficult to manage in these sizes and rare to find in a 300kCMIL size (the equipment lugs could not handle 350kCMIL, and could not be changed out). Article 392 indicates that single conductor cable over 1/0 AWG is suitable for installation in tray as long as labeled as suitable for use with tray, but section 501.10 indicates that only types PLTC, PLTC-ER, ITC, ITC-ER, MC, MV or TC bay be installed in division 2 hazardous locations.

The 1/C cable is "CT" rated (Suitable for use in Cable Tray), but I don't think it is possible to have a TC rating for a single conductor cable since article 336 defines TC rated cable as "A factory assembly of two or more insulated conductors..."

I always took CT as the same as TC, but by the letter of the code, I can now see they are not really the same.

I have been doing these types of installations for many years, and so have many of my colleagues and this is the first time this has come up. Has anyone come across this before?

Thanks in advance for any sage like wisdom here...
 

Dennis Alwon

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Location
Chapel Hill, NC
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Retired Electrical Contractor
I think many people have trouble with the CT- cable tray- meaning the tray itself and TC- tray cable- meaning the cable made to be installed in the cable tray (CT)
 

rbalex

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Location
Mission Viejo, CA
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Professional Electrical Engineer
Ya gotta love English ambiguity and unintended consequences in the NEC. Single conductors marked "for use in cable trays" or "CT use" and "sunlight resistant" (if necessary), installed per Article 392 and stress relieved at the terminations are suitable for Class I, Division 2. There is no sound technical reason to believe otherwise.

It was much clearer before CMP7 and CMP8 started uncoordinated monkeying with Articles 336 and 392 respectively (shame on the TCC) and CMP14 thought they needed to list each specific wiring method in trays rather than simply saying in 501.10(B) "wiring methods permitted per Article 392" or its previous equivalent [Article 318 before 2002]. The "uncoordinated monkeying" started more that 15 years ago and virtually every attempt to "clarify" issues have only muddied the waters more.

One might also review it under Section 500.8(A) as an engineering evaluation. Anyone that doesn't recognize this as suitable isn't sufficiently "trained" [Section 90(C)] to be working with classified locations.
 
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osiris42

Member
Location
Denver, CO
Thank you for the responses. As you stated, I see no technical justification for the exclusion of single-conductor cables in Division 2 areas, but without anything to back that up, it comes down to a code call by the AHJ.

It's always interesting how something can be common practice and yet against the letter of the code. I guess it just takes someone looking at it with fresh eyes to see the gaps.
 

rbalex

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Mission Viejo, CA
Occupation
Professional Electrical Engineer
... As you stated, I see no technical justification for the exclusion of single-conductor cables in Division 2 areas, but without anything to back that up, it comes down to a code call by the AHJ...
That's why I told you to review Section 500.8(A) - specifically, 500.8(A)(3). If you don't have the confidence to make that engineering judgment, you are an example of trying to make the Code a "design specification or instruction manual". [Section 90.1(C)]

I was on CMP14 when the original text of Section 500.8(A) was developed - primarily for just this kind of issue. For two Code cycles, the IAEI demanded that all classified location equipment be listed or labeled for classified locations (even Division 2) because inspectors didn't necessarily know what they were looking at. They settled for identified, assuming that it meant listed or labeled; it doesn't. However, CMP1 and the TCC wouldn't permit that clarification in Art 100 definition. Eventually they added the FPN/IN to the definition of identified to "clarify" the issue as a response to CMP14 defining suitable with respect to classified locations.

EDIT ADD: It actually isn't against the letter of the Code [Section 500.8(A)(3)] or even the "spirit" or "intent" of the Code. Engineers should be willing to accept the responsibility of their designs.
 
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osiris42

Member
Location
Denver, CO
I fully understand the need to take responsibility for designs, and am wiling to do that every time I stamp a drawing. However, in this particular case the AHJ was the owner's inspector and he wouldn't sign on off on it regardless of the technical justifications. Sometimes it's not up to just the engineer, the AHJ has to accept it as well, and in this case they wouldn't.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
OTOH, there are a lot of places in the code where there are specific requirements that are well beyond what is required for a safe installation and you have to abide by them as well. This kind of thing is mucked up enough that I can understand why an inspector might take the view that unless the wiring method is included in the article you can't use it.

There seems to be an out here for an AHJ that is willing to accept engineering judgement. However, i would point out that the inspector is not the AHJ and thus has no authority in general to accept anything beyond what is in the code unless the actual AHJ says he can and as far as I know, none of them delegate that authority to any inspector.
 
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