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Thread: Romex derating /romex wire type

  1. #11
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    Quote Originally Posted by infinity View Post
    Do you have a specific code section?
    Isn't because they don't have wire markings?

  2. #12
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    Quote Originally Posted by Coppersmith View Post
    Isn't because they don't have wire markings?
    Yeah that is one, but its also more than that. NM inners are not article 310 conductors.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  3. #13
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    Quote Originally Posted by electrofelon View Post
    NM inners are not article 310 conductors.
    I checked a bunch of data sheets on NM cable from different manufacturers. Most just say the conductors have PVC insulation; one says they have PVC insulation of the thickness required for THHN conductors; and CME Cable's datasheet says "Single conductors are dual rated THHN/THWN, meeting 90 °C Dry, 75 °C Wet." ( http://www.cmewire.com/catalog/sec01-bwx/bwx-09-nmb.pdf )

    So with CME Cable's product, would you still have an objection?

    Cheers, Wayne

  4. #14
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    Quote Originally Posted by wwhitney View Post
    I checked a bunch of data sheets on NM cable from different manufacturers. Most just say the conductors have PVC insulation; one says they have PVC insulation of the thickness required for THHN conductors; and CME Cable's datasheet says "Single conductors are dual rated THHN/THWN, meeting 90 °C Dry, 75 °C Wet." ( http://www.cmewire.com/catalog/sec01-bwx/bwx-09-nmb.pdf )

    So with CME Cable's product, would you still have an objection?

    Cheers, Wayne
    That CME datasheet is the first and only spec I have seen that says the inners are THWN. If so , I dont have a problem with it, although they still may not meet the marking requirements. (Note Actually, I dont have a problem with it even if the manufacturer doesnt state they are THHN - I did say it was a nit picky silly technicality )
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  5. #15
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    One could even argue that stripping NM in boxes isn't compliant, not to mention in panels.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  6. #16
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    Quote Originally Posted by electrofelon View Post
    Its a bit of a mystery whats inside ramen. No one really knows what type of conductors the inners are. But yes I agree with Rob, 334 tells us what the temperature rating is.
    No mystery.....UL 719 is clear....it is THHN/THWN-2 (more THHN) equivalent. No markings are required on the conductors because it is not permitted to be stripped out for use in raceways. However, the implying it can't be stripped out at termination is foolish. The standard permits the markings on the sheathing so at termination they can be exposed for final termination.

  7. #17
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    Quote Originally Posted by MasterTheNEC View Post
    No mystery.....UL 719 is clear....it is THHN/THWN-2 (more THHN) equivalent.
    Are you sure? I would like to see the language if you can post that sentance. UL719 is copyrighted and costs like $500 so I have never seen the wording. The sections I have seen , do not state such.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  8. #18
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    Quote Originally Posted by electrofelon View Post
    Are you sure? I would like to see the language if you can post that sentance. UL719 is copyrighted and costs like $500 so I have never seen the wording. The sections I have seen , do not state such.
    LOL..umm...Im sure as I am kinda intimate with UL 719.

    But since I am usually fibbing....lol....here you go.


    4.3.3 An 8 AWG or larger circuit conductor and a 6 AWG or larger grounding conductor shall be stranded.
    Conductors shall comply with the requirements in the "Conductors" Section of the Standard for
    Thermoplastic-Insulated Wires and Cables, UL 83 except as modified in this section.


    4.3.4 A joint in a solid conductor or in one of the individual wires of a stranded conductor shall be made
    in a workmanlike manner and shall not increase the diameter of the solid conductor, the individual wire
    strand, or the overall stranded conductor. A joint shall not be made in a stranded conductor as a whole
    but shall be made by separately joining each individual wire. A joint shall be made only before coverings,
    if any, are applied to an insulated conductor. The insulation applied to such joints shall be equivalent to
    that removed and, if of PVC, shall have insulation-resistance (K = 4000 at 15.6°C or 60.0°F) and
    dielectric-withstand characteristics complying with the requirements for the thermoplastic-insulated wire.


    4.4 Insulation


    4.4.1 Both before and after assembly into finished cable, the insulation employed on the circuit
    conductors shall comply with (a) or (b):


    a) THHN Construction – Jacketed insulation for a Type NM or NMC cable shall have a nylon or
    similar jacket and shall comply with the thickness and other applicable requirements for Type
    THHN thermoplastic-insulated wire without (see 6.2.4) any surface marking of 'THHN", "-B", or
    any ampacity or temperature rating.


    b) TW Construction – Insulation without a nylon jacket shall comply with the thickness
    requirements for a Type TW thermoplastic-insulated wire. The insulation material shall comply
    with (1) or (2):


    1) For TYPE NM or Type NMC Cable – The insulation material shall be a dry-locations
    PVC that complies with the requirements for Type THHN insulation without any surface
    marking of the ampacity or temperature rating (the surface marking "-B" is optional on
    the insulation). The tensile strength and elongation are to comply with the “Physical
    properties of PVC insulation from Type TFN and TFFN fixture wires" Table in UL 1581.
    The deformation test is to be conducted at 121.0 ±1.0°C (249.8±1.8°F) with a decrease
    of not more than 50 percent in the thickness of the PVC insulation.


    2) For TYPE NM only – Type NM is eligible to use a thermoplastic insulating material
    other than PVC. The performance and ratings of the material as insulation shall be
    determined by investigation and shall be:


    i) Electrically comparable to the PVC insulation in Type THHN wire, and


    ii) Mechanically comparable to the nylon or similarly jacketed PVC insulation of
    Type THHN wire, and


    iii) In accordance with “Physical properties of insulation of thermoplastic other
    than PVC from Type NM cables” Table in UL 1581.

  9. #19
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    Thanks for posting that. I am still not seeing that is necessarily THHN. There is an awful lot or wording there: "comparable to" "complies with" when they could have just said "conductors shall be THHN"
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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