tc cable div 2 sealing requirements

[bozo]

My question is: are cable seals required on a multiconductor TC cable terminated at a terminal box (sheet metal) in a Class I Div. 2 area with the other end terminating in an unclassified area. My interpretation of 501.15(E)(1) is that a seal would be required in the Div. 2 area with the terminal box being the best location. However, the wording in 501.15(E)(1) as well as the title (Terminations) has me a little confused. The second sentence ("Multiconductor cables with a gas/vaportight continuous sheath capable of transmitting gases or vapors through the cable core shall be sealed in a listed fitting in the Division 2 location after removing the jacket and any other coverings so that the sealing compound surrounds each individual insulated conductor in such a manner as to minimize the passage of gases and vapors.") appears to address the issue of cable sealing for a boundary change, which is my question, but the fact that this appears in an article section entitled "Terminations" has me a little confused and wondering if my interpretation is correct. Any help would be appreciated.

 

[rbalex]

The first sentence in 501.15(E)(1) tells you when cables are required to be sealed ("Cables entering enclosures that are required to be explosionproof ...); the rest of the Section describes how they are required to be sealed, if necessary. In other words, if the enclosure isn't required to be sealed, the rest of the Section doesn't apply. "

BTW the UL Whitebook will tell you that Type TC and various other cable types have a "gas/vaportight continuous sheath,"but it won't tell you whether they are capable of transmitting gases or vapors through the core. ATM, for all practical purposes Section 501.15(E)(2) is useless.

 

[bozo]

The first sentence in 501.15(E)(1) tells you when cables are required to be sealed ("Cables entering enclosures that are required to be explosionproof ...); the rest of the Section describes how they are required to be sealed, if necessary. In other words, if the enclosure isn't required to be sealed, the rest of the Section doesn't apply. "

BTW the UL Whitebook will tell you that Type TC and various other cable types have a "gas/vaportight continuous sheath,"but it won't tell you whether they are capable of transmitting gases or vapors through the core. ATM, for all practical purposes Section 501.15(E)(2) is useless.

Thanks for the reply. If the multiconductor sentence is just elaboration on how they are required to be sealed, then why does it say "in the Division 2 location", which is describing where the seal it to be located? This phrase would seem to be completely unnecessary and in fact misleading (to me), since the first sentence clearly states "at the point of entrance". The Commentary Table 501.1 in the handbook seems to reinforce my likely mistaken belief that the multiconductor statement is a separate issue from the enclosure sealing issue because it lists them as separates items.

Thanks again.

 

[rbalex]

... If the multiconductor sentence is just elaboration on how they are required to be sealed, then why does it say "in the Division 2 location", which is describing where the seal it to be located? ...

It simply means the cable seal must be on the classified, rather than unclassified end.

.. This phrase would seem to be completely unnecessary and in fact misleading (to me), since the first sentence clearly states "at the point of entrance". The Commentary Table 501.1 in the handbook seems to reinforce my likely mistaken belief that the multiconductor statement is a separate issue from the enclosure sealing issue because it lists them as separates items...

The wording may be unnecessary, it may be ambiguous, but the Section is talking about seals to maintain the enclosure integrity. If the enclosure doesn't need to be explosionproof, sealing the cable has no more benefit than sealing a raceway under the same conditions.

 

[bozo]

It simply means the cable seal must be on the classified, rather than unclassified end.

Thanks for the reply. If, as you mention, they are specifying at which end of the cable to place the seal, it sounds like they are addressing a boundary change issue, not a seal requirement at an enclosure, which as stated in the first sentence of the article, has to be at the point of entrance to the enclosure. I'm afraid it makes no sense (to me) to say "in the Division 2 location" if you're talking about seals at enclosures in Div. 2 locations. I've never heard of a seal required at an enclosure being allowed to be at the other end of the conduit or cable, so why would they put that phrase in unless they are talking about sealing for a boundary change?

Thanks again. Not trying to be argumentative, but the wording in this article really seems misleading.

 

[bozo]

If the enclosure doesn't need to be explosionproof, sealing the cable has no more benefit than sealing a raceway under the same conditions.

Possibly, unless however you are sealing to prevent migration of gases through the cable core into an unclassified area.

 

[bozo]

Here is additional info that I believe rather conclusively indicates that the code requires cable seals for multiconductor cables with a gas/vaportight continous sheath capable of transmitting vapors through the core at any div. 2 area termination (not just at explosionproof enclosures). After further scrutinizing the rest of 501.15(E), I noticed that in 501.15(E)(2) the code is saying that cables with a gas/vaportight continuous sheath and do not transmit gases or vapors through the core are not required to be sealed, except at a required explosionproof enclosure. However, the cable length has to be great enough for the cable to limit the gas or vapor flow through the core to the same flow rate permitted for seal fittings. In other words, the cable has to perform the same function as a seal in terms of allowing passage of gases or vapors.
Then, if you look at 501.15(E)(3) Cables Capable of Transmitting Gases or Vapors, which is the same category as our multiconductor, it states that these cables have to comply with 501.15(E)(1) Terminations but otherwise do not require a seal except if connected to process equipment or devices that may cause a pressure in excess of 6 in. of water (the seal performance limit). (This condition is addressed in 501.17 Process Sealing.)
So, if you take the stance that 501.15(E)(1) is saying cable seals are only required at explosionproof enclosures and the sentence about multiconductors being sealed in the div. 2 area is only telling how to seal at the explosionproof enclosure, hence no seal is required at any other termination, then apparently the code is saying:
1) A cable that cannot transmit gases through the core has to perform the same function as a seal to limit the passage of gases or vapors;
2) A cable that can transmit gases through the core, nope, no seal required, we don't really care if gases or vapors are transmitted from a Div. 2 area to an unclassified one.
As Spock would likely say, this seems highly illogical.

My only logical conclusion is that 501.15(E)(1) is explaining the seal requirement at terminations for two different conditions: 1) Explosionproof Enclosures, and 2) All terminations of a multiconductor with gas/vaportight continous sheath capable of transmitting vapors through the core.

However, I do find it puzzling that not in any of the previously mentioned code sections does it mention the condition of the other end of the cable terminating in an unclassified area. Unless this condition is present, I would assume there would be no requirement for any sealing (except to complete explosionproof integrity of an enclosure, of course). Hopefully, the wording will be improved in future code cycles to at least minimize confusion. If my interpretation is correct, I am pretty sure that there are many cables not sealed that should be.

 

[nollij]

This thread very handily covers exactly what you are talking about:

http://forums.mikeholt.com/showthread.php?t=128228&highlight=


But, in summary:

Here is the section from the book that I mentioned in the 4th post:
"Even cables that have a core capable of transmitting gases or vapors in excess of the amount permitted for conduit seals are unlikely to transmit gases and vapors through the core unless there is a pressure differential between the end of the cable in the Division 2 location and the end of the cable in the nonhazardous location so as to force the gases and vapors through the core. The National Electrical Code recognizes this by indicating that a cable with a gas/vapor-tight jacket that is capable of transmitting gases or vapors through the cable core is not required to be sealed unless either it requires a seal because the cable enters an explosionproof enclosure, or the enclosure in the hazardous location is pressurized in such a manner as to subject the cable to a pressure in excess of 6 inches of water (1493 pascals, 0.2166 psi). In this respect, cables are not treated the same as insulated conductors in conduit."

Also, manufacturer's engineer reply to my request concerning 501.15(E)(2):
"The gas/vapor transmission rate or capability is also a mystery requirement. All multi-conductor cables are manufactured and assembled using various types of filler packing of the core, grounding conductors, binder tapes and lay-up of the core conductors. These cables are bent to varying degrees during installation and are trained in their final position assuming various bent configurations. All of this discussion points to the conclusion that all cables pass gas(excuse the pun). UL has not developed or requires any type of internal gas transmission rate tests. Manufacturer has not conducted any type of tests where we can say one test of one representative cable assembly represents all other assemblies."

 

[bozo]

If you interpret 501.15(E)(1) to say that Multiconductor cables with a gas/vaportight continuous sheath capable of transmitting gases or vapors through the cable core do not require sealing in the div. 2 area unless they terminate at a required explosionproof enclosure, then please explain the following:
1) In the third sentence of 501.15(E)(1) why does it say "in the div. 2 location"? If this is just explanatory info on how to seal at the explosionproof enclosure, this phrase is completely unnecessary and misleading because the first sentence states the seal has to be at the enclosure (which we already know is in a div. 2 area).
2) The existence of Exception No. 1: Cables passing from an enclosure or room that is unclassified as a result of Type Z pressurization into a Class I, Division 2 location shall not require a seal at the boundary. If a seal isn't required on the multiconductor anyway, why would they bother to put in an exception not requiring a seal under that condition. Makes absolutely no sense to me.
3) The requirement in 501.15(E)(2) that cables that do not transmit gases or vapors through their core still have to be long enough to limit the gas or vapor flow to the rate permitted for seal fittings. Why would this be important if a seal isn't even required on cables that are capable of transmitting gases or vapors through the core?
4) In the first Handbook expanatory note following 501.15(E)(2), (page 741 of 2011 Handbook) it states "If there is any concern that the cable run is capable of transmitting gases or vapors through the core, a sealing fitting should be installed." Why state this after they have supposedly definitively said no seal is required.
5) Here is a quote from IEEE 1242 Guide for Specifying and Selecting Cable for Petrochemical Plants: "Other Cables: Unlike Type MI cable, other types of cables do not block the passage of flammable or combustible gases, vapors, or liquids. Therefore, conduits and seals must be used on cables to prevent the passage of such gases, vapors and liquids."

 

[bozo]

Here is an additional question I have for those that interpret 501.15(E)(1) to say that Multiconductor cables with a gas/vaportight continuous sheath capable of transmitting gases or vapors through the cable core do not require sealing in the div. 2 area only if they terminate at a required explosionproof enclosure: What is the reason for the exception to 501.15(E)(3) "Cables with an unbroken gas/vaportight continuous sheath shall be permitted to pass through a Class I, Division 2 location without seals." Why would they need an any exception if no seal is required to start with?

 

[bozo]

Here are some more rambling thoughts on the subject.
1) In a Div. 1 area multiconductor Type MC-HL cables are required to be sealed at all terminations, including at enclosures that do NOT require conduit seals, such as terminal boxes (except for conduits 2" & greater). This indicates to me that there is serious concern about the transmission of gases or vapors out of the Div. 1 area. It seems counter-intuitive for them to then say that in a div. 2 area there is absolutely no need to seal in order to prevent the transmission of gases or vapors, and in addition, list exceptions that are completely irrelevant, unnecessary and misleading if seals are not required to begin with. But let's assume for a minute that this is what they have done. Since this position seems quite illogical, why would they not explain their logic or thinking in at least an explanatory note of the Handbook?

 

[bozo]

Here's another stab at trying to prove my point (that multiconductor cables capable of transmitting gases or vapors through their core must be sealed at all terminations in a Div. 2 area when the other cable end terminates in an unclassified area). Those that disagree appear to be basing their interpretation on the verbage in the third sentence of 501.15(E)(1). This sentence, they claim, is simply clarifying HOW to seal a multiconductor at a required explosionproof enclosure and this is the only time a multi is required to be sealed in a Div. 2 location [except for maybe the somewhat improbable situation addressed in 501.15(E)(3)]. In summary, they are saying that multiconductors do not require sealing due to an area classification boundary change.

In 501.15 Informational Note No. 1 it quite clearly identifies the two purposes of conduit and cable seals: "Seals are provided in conduit and cable systems to minimize the passage of gases and vapors AND prevent the passage of flames from one portion of the electrical installation to another through the conduit." Therefore, it seems quite obvious that seals at required explosionproof enclosures are there to prevent the passage of flames (contain an explosion), and seals necessary for an area class boundary change are there to prevent the passage of gases and vapors.

OK, then please explain the the following verbage in the third sentence of 501.15(E)(1): "in such a manner as to minimize the passage of gases and vapors". This seems clearly to designate that the seal is functioning for a boundary change, otherwise it should have said "in such a manner as to prevent the passage of flames".

To summarize, this third sentence of 501.15(E)(1) has two phrases ("in the Division 2 location" and "in such a manner as to minimize the passage of gases and vapors") which make no sense if you are interpreting this sentence to only be clarifying how to seal at the explosionproof enclosure. However, they make perfect sense if you interpret this sentence to be an additional condition where cables are required to be sealed.

In addition, all the previously mentioned (in other posts) exceptions and expanatory note now make sense instead of being head scratchers.

 

[bozo]

For what this is worth, I submitted this question to an NFPA staff member for his (informal) interpretation, and after searching the ROPs to see if there are any upcoming changes that would impact this issue (there aren't), he agreed with my interpretation: 501.15(E)(1) is requiring seals for multiconductors (with a gas/vaportight continuous sheath capable of transmitting gases or vapors through the cable core) at ALL terminations in a Division 2 location (of course with the exception described in "Exception No. 1") in addition to the requirement for sealing all cables entering a required explosionproof enclosure.

 

[BPoindexter]

Mike,

I believe your assessment to be correct. I have worked in C1D1 and C1D2 facilities for the past 20 years and that is how we and the AHJ's have always interpreted it. If the cable is capable of transmitting gases and crosses a boundary into a different classified location, in this case unclassified, then it is required to be sealed regardless of the enclosure type. Typically we use MC-HL and use TMCX connectors at the C1D2 location to accomplish this. For TC cable we use a gas blocking kit. For instrument cables that have a sheath inside the MC in addition to using a TMCX we bring the sheath through the TMCX intact and then install a gas blocking kit on the sheath inside the enclosure. Typically we use NEMA 4X for C1D2 where explosionproof is not required i.e. no arcing/sparking/heat generating devices.

 

[bozo]

Mike,

I believe your assessment to be correct. I have worked in C1D1 and C1D2 facilities for the past 20 years and that is how we and the AHJ's have always interpreted it. If the cable is capable of transmitting gases and crosses a boundary into a different classified location, in this case unclassified, then it is required to be sealed regardless of the enclosure type.

Thanks for the reply. I can't help but wonder if we're part of the majority or minority.

 

[bozo]

If I were to play devils advocate for a moment and represent the interpretation that multiconductors are not required to be sealed for a boundary change, I would say, wait a minute, if 501.15(E)(1) is requiring seals at all terminations in a division 2 location then please explain 501.15(E)(3) which states cables capable of transmitting gases or vapors are not required to be sealed except as required in 501.15(E)(1) and if all of these cables are required to be sealed anyway the wording "unless the cable is attached to process equipment ..." is meaningless. I'm afraid the only way I can interpret this section to make any sense and still agree with my interpretation is to say there is one subset of these types of cables not mentioned in 501.15(E)(1). That subset would be single conductors cables. So my interpretation is that this section is essentially saying that single conductor cables do not require sealing unless the cable is attached to process equipment ...