Gas/Vaportight Continuous Sheath vs Jacket -Boundary Seal b/w Div. 2 and unclassified

[ClayH]

I had a bit of an argument the other day on the interpretation of the following and was wanting to get others feedback.

I am referencing NFPA 70 - 2014 edition. 501.15 (E)(4) in reference to cable seals in a Class I Division 2 location. NEC allows for type TC-ER cable to be utilized in a CID2 location. The section reference above states that if cable does not have a gas/vapor tight continuous sheath, it shall be sealed at the unclassified boundary in a way that minimizes the passage of gases or vapors.

The question is the terminology that is used defines sheath. Sheath generally relates to a form of armor or welded sheath of a cable, which you will see for MC-HL (Gas/vapor-tight continuous metallic sheath). Or can sheath also be for the outer jacket of a non-armored cable.

Example being, an unarmored TC-ER cable can being utilized in a CID2 location, which is acceptable per NEC. The data sheet of the TC-ER cable defines that it has a gas/vapor tight jacket. (Difference in terminology) Would this cable comply with the requirement of 501.15 (E)(4) for "gas/vapor tight continuous sheath", thus would not require a seal at the boundary b/w CID2 and unclassified location. For arguing sake, there would still be a seal around the cable exterior, but not for the core of the conductor(s).

 

[rbalex]

The problem arises because various terms are UL related, some are NEMA related, and others are NEC related and there is nothing to compel the various entities to be consistent with each other.

Within the NEMA cable world, a “jacket” offers mechanical protection and a “sheath” only holds the conductors in a multiconductor arraignment together. SO – a jacket will usually also be a “sheath”.

The UL Whitebook says in Category Code QPOR:

Regarding cable seals outlined in Article 501 of the NEC, Type TC cable has a sheath which is considered to be gas/vapor tight but the cable has not been investigated for transmission of gases or vapors through its core.

Basically, Section 501.15(E)(2) is useless. Section 501.15(E)(3) covers Type TC in its various forms. No boundary seal is necessary but, depending on the NEC Edition, you may need to parse Section 501.15(E)(1) carefully to arrive at that conclusion. The 2014 Edition is particularly muddled.

 

[ClayH]

Thank you, very helpful.