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Thread: cable in conduit cable end seals

  1. #21
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    anybody else have thoughts on this?

  2. #22
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    Quote Originally Posted by Wire-Smith View Post
    why don't you try reading the code book?
    I’d advise you to do the same. According to you anything the AHJ happens to like - tape, cold shrink etc could be “approved” - the seal
    Has to block gases from entering the internal part of the cable -


    Sent from my iPhone using Tapatalk

  3. #23
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    Quote Originally Posted by Wire-Smith View Post
    anybody else have thoughts on this?
    Sure, but I thought I'd let you two take it outside and duke it out.

    It's important to recognize an Exception does not necessarily wipe out the main text entirely. From Section 501.15(D)(2) main text:

    Cables Capable of Transmitting Gases or Vapors.
    Cables with a gas/vaportight continuous sheath capable of
    transmitting gases or vapors through the cable core, installed
    in conduit, shall be sealed in the Class 1, Division 1
    location after the jacket and any other coverings have been
    removed so that the sealing compound can surround each
    individual insulated conductor
    or optical fiber tube and the
    outer jacket
    .
    Here we see the method of sealing must surround both the conductors AND the outer jacket.

    From the Exception:

    Exception: Multiconductor cables with a gas/vaportight
    continuous sheath capable of transmitting gases or vapors
    through the cable core shall be permitted to be considered
    as a single conductor by sealing the cable in the conduit

    within 450 mm (18 in.) of the enclosure and the cable end
    within the enclosure
    by an approved means to minimize the
    entrance of gases or vapors and prevent the propagation of
    flame into the cable core, or by other approved methods. It
    shall not be required to remove the shielding material or
    separate the twisted pairs of shielded cables and twisted
    pair cables.
    This is primarily for the benefit of boundary seals to permit them to be treated as a single conductor at the boundary without needing to remove the jacket; however, the same benefit may be achieved at the enclosure IF the outer jacket is included within the overall internal sealing method within the enclosure. In other words, the conductors AND the outer jacket must still be within the same sealing method inside the enclosure. The additional note about shielded. twisted pairs is just an addendum.

    In the rare case (which I avoid like the plague) where I have had to use multiconductor cable in conduit, I have used a shrinkon sleeve with an internal melting mastic.

    As an interesting side note, read the last sentence of Section 501.15(E)(1) for Division 2 applications.

    Next question: How do you know you have, "A cable with a gas/vaportight continuous sheath".
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  4. #24
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    Quote Originally Posted by rbalex View Post
    Sure, but I thought I'd let you two take it outside and duke it out.

    It's important to recognize an Exception does not necessarily wipe out the main text entirely. From Section 501.15(D)(2) main text:

    Here we see the method of sealing must surround both the conductors AND the outer jacket.

    From the Exception:

    This is primarily for the benefit of boundary seals to permit them to be treated as a single conductor at the boundary without needing to remove the jacket; however, the same benefit may be achieved at the enclosure IF the outer jacket is included within the overall internal sealing method within the enclosure. In other words, the conductors AND the outer jacket must still be within the same sealing method inside the enclosure. The additional note about shielded. twisted pairs is just an addendum.

    In the rare case (which I avoid like the plague) where I have had to use multiconductor cable in conduit, I have used a shrinkon sleeve with an internal melting mastic.

    As an interesting side note, read the last sentence of Section 501.15(E)(1) for Division 2 applications.

    Next question: How do you know you have, "A cable with a gas/vaportight continuous sheath".
    Bob
    The OP is routing multiconductor (most likely type TC) cable within conduit - from our previous discussions, UL White Book, QPOR, pg 351 states:
    "Regarding cable seals outlined in Article 501 of the NEC, Type TC cables has a sheath which is considered to be gas/vaportight but the cable has not been investigated for transmission of gases or vapors through its core". The cable would therefore fall under 501.15(E)(1) which refers you back to 501.15(D)(1) thru 501.15(D)(3) - which includes 501.15(C)(1) - and this is where the true definition of "approved means' is described as a 'compound'.I also recall, MI cable - which is rarely used for power applications - is considered to be the only true gas/vapor blocked cable available.



  5. #25
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    Previous discussion and guidance from rbalex.

    http://forums.mikeholt.com/showthrea...01.15+%2Bnhee2

    I have not interpreted the approved means in 501.15(D)(1) exception to require TCMX or chico, but that interpretation was influenced by the thread above.

  6. #26
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    Quote Originally Posted by nhee2 View Post
    Previous discussion and guidance from rbalex.

    http://forums.mikeholt.com/showthrea...01.15+%2Bnhee2

    I have not interpreted the approved means in 501.15(D)(1) exception to require TCMX or chico, but that interpretation was influenced by the thread above.
    So I can see 'approved means' has a myriad of interpretations. I still believe the best (and safest) way to seal a TC cable end within a conduit is to use a compound with a "melting point of not less than 200 degrees F", surrounding all individual conductors so as to prevent passage of vapor via the cable intricacies. I believe this is what the NEC advocates.

  7. #27
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    Dale001289 and nhee2 - good work you two. The critical point is the multiconductor cable (in conduit) jacket is sealed in the same "mass" as the conductors at the cable's end. It actually applies even when the multiconductor cable isn't in a conduit - it's just easier to accomplish.

    It may also be relevant to know that I use Section 500.8(A)(3) when I'm forced to seal such a cable. I also spend a bit of time with the local AHJ in advance to assure acceptance. I never had a problem.

    In addition, while shielded/twisted pairs have their own general exception, the truth is, many multiconductor cables of any Type construction may "gas block" sufficiently on their own in as little as 10 feet. But neither UL nor the manufacturers are willing to state just what that minimum length may be for any given cable construction/installation. There are just too many variables. SO - I just say forget Sections 501.15(D)(3) and E(2) since they only apply to Type MI and it has its own specific installation rules anyway [Section 501.10(A)(1)(b)]. Section 501.15(E)(2) does have some value since it describes the acceptable "leak rate". (IMO that should be in somewhere in Section 501.15(C), but that's just my opinion.)
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  8. #28
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    Quote Originally Posted by rbalex View Post
    Dale001289 and nhee2 - good work you two. The critical point is the multiconductor cable (in conduit) jacket is sealed in the same "mass" as the conductors at the cable's end. It actually applies even when the multiconductor cable isn't in a conduit - it's just easier to accomplish.

    It may also be relevant to know that I use Section 500.8(A)(3) when I'm forced to seal such a cable. I also spend a bit of time with the local AHJ in advance to assure acceptance. I never had a problem.

    In addition, while shielded/twisted pairs have their own general exception, the truth is, many multiconductor cables of any Type construction may "gas block" sufficiently on their own in as little as 10 feet. But neither UL nor the manufacturers are willing to state just what that minimum length may be for any given cable construction/installation. There are just too many variables. SO - I just say forget Sections 501.15(D)(3) and E(2) since they only apply to Type MI and it has its own specific installation rules anyway [Section 501.10(A)(1)(b)]. Section 501.15(E)(2) does have some value since it describes the acceptable "leak rate". (IMO that should be in somewhere in Section 501.15(C), but that's just my opinion.)

    Thanks for this invaluable input. 500.8(A)(3) may be the best route to take on cable seals.

  9. #29
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    Quote Originally Posted by rbalex View Post
    The critical point is the multiconductor cable (in conduit) jacket is sealed in the same "mass" as the conductors at the cable's end. It actually applies even when the multiconductor cable isn't in a conduit - it's just easier to accomplish.

    I'm confused by this statement - what are you considering the 'mass'? Mass of sealant?

    For an explosion-proof transmitter with a twisted shielded pair - I interpret this can be an EY type seal fitting with cable and chico (no stripping of insulation), with cable continuing through < 18" of conduit/fittings to the transmitter. Cable jacket stripped at transmitter, and heat shrink the cable ends with adhesive backed heat shrink (assuming the AHJ 'approves'). Is this consistent with what you are saying?
    Last edited by rbalex; 05-30-18 at 04:07 PM. Reason: Clean up quotation

  10. #30
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    Quote Originally Posted by nhee2 View Post


    I'm confused by this statement - what are you considering the 'mass'? Mass of sealant?

    For an explosion-proof transmitter with a twisted shielded pair - I interpret this can be an EY type seal fitting with cable and chico (no stripping of insulation), with cable continuing through < 18" of conduit/fittings to the transmitter. Cable jacket stripped at transmitter, and heat shrink the cable ends with adhesive backed heat shrink (assuming the AHJ 'approves'). Is this consistent with what you are saying?
    Sorry I confused you. I still couldn't find the illustration I mentioned four years ago. I've attached two pictures I hope will help.

    Click image for larger version. 

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    On the left side is "standard" Type TC. The red block represents the enclosure seal and the blue represents what the sealing material required "within" the enclosure must surround.
    Similarly, the right side is a multi-pair, type instrument cable. I have used violet to indicate there may also be an individual jacket for each pair.

    The reality is, triads and quads should also be included, and shielding and twisting aren't absolutely necessary either, but the CMP didn't want to write up every conceivable construction possible for instrument cables.

    For a cable only application, a TMCX will provide both the red and blue seal. For a cable in conduit application, an EYS or similar could also achieve both, but it's STILL A REAL PAIN and I avoided it whenever possible.

    BTW, the insulation never needs to be removed, only the jacket and/or sheath. In fact, the cement type sealing material is slightly conductive.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

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