Romex derating /romex wire type

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danickstr

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Hey guys. I know romex is nm-b but what temperature wire type is the actual conductor. Is it thh type for high heat? I know it doesn’t have a nylon jacket so it isn’t thhn. I think it derates at 90 degrees but wanted some expert input. Thanks.
 
Yes the conductors are rated for 90° C but the cable can only be used at its 60° C ampacity. The 90° C rating is OK for derating purposes. Take a look at 334.80.
 
It probably isn't exactly kosher to take the wires out of the jacket and use them as pigtails, however I bet every house in existence that has any wire extension or pigtails to switches and receptacles is by Romex that's been stripped down.
 
JFletcher said:
It probably isn't exactly kosher to take the wires out of the jacket and use them as pigtails, however I bet every house in existence that has any wire extension or pigtails to switches and receptacles is by Romex that's been stripped down.
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What's the problem with doing that, is it any different than attaching directly to the NM conductors in the box?
 
JFletcher said:
It probably isn't exactly kosher to take the wires out of the jacket and use them as pigtails, however I bet every house in existence that has any wire extension or pigtails to switches and receptacles is by Romex that's been stripped down.
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electrofelon said:
Although a real nitpicky and ridiculous thing, Theoretically I do agree with JF. NM inners are not article 310 conductors.
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Do you have a specific code section?
 
electrofelon said:
NM inners are not article 310 conductors.
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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
 
wwhitney said:
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
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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 :))
 
electrofelon said:
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.
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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.
 
electrofelon said:
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.
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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.
 
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