Types of conductors inside Romex cable

[jeff48356]

Are the individual conductors inside a piece of 14/2 or 12/2 Romex cable THHN or THWN type? What about those inside of an 8-3 or 6-3 Romex?

 

[Ponchik]

THHN

 

[A/A Fuel GTX]

The conductors are not marked but the general consensus is that they are THHN.

 

[K8MHZ]

Are the individual conductors inside a piece of 14/2 or 12/2 Romex cable THHN or THWN type? What about those inside of an 8-3 or 6-3 Romex?

If they are not marked as individual conductors, it makes no difference as far as the code goes.

For just curiousity, check the Southwire web site for Romex specs. Essex may have different specs if you are using Romex as a generic term.

 

[augie47]

Southwire describes their construction as follows:
The construction is manufactured using annealed (soft) copper conductors?compressed
stranding for the stranded conductors; a 90?C rated thermoplastic polyvinyl chloride (PVC)insulation and a nylon jacket for the individual conductors; and a PVC jacket surrounding the overall construction
Basically the insulation meet the required criteria for the listing. It is neither THHN or THWN and as such is not listed as an individual conductor to be installed in a raceway, etc.

 

[Ponchik]

? Southwire?s Romex? SIMpull? Type NM-B cable is manufactured as 2, 3, or 4 conductor cable, with a ground wire ? Copper conductors are annealed (soft) copper ? Stranded conductors are compressed stranded ? Conductor insulation is 90?C-rated polyvinyl chloride (PVC), nylon jacketed ? The cable jacket is color-coded for quick size identification; White - 14 AWG, Yellow - 12 AWG, Orange - 10 AWG, and Black - 8 AWG and 6 AWG ? Unique SIM (SlikQuik? Infused Membrane) Jacket? construction allows for 50% reduction in pulling force resulting in easier installation, easier stripping, reduced burn-thru, and tear resistance

 

[fmtjfw]

Old old romex (NM, not NM-B) used TW wire and the conductors were often marked, but the cable was not rated for wet locations.

 

[mopowr steve]

Hey Augie, just for sake of gettin everybody in a uproar could you also tell us what the specs are for THHN insulation and THWN insulation, do they in fact specify 90* thermoplastic polyvinyl chloride with nylon jacket type insulation?
And if so, the conductors in NM-B cable are in fact the same even though the cable is not listed for use in wet location.
Next question, has anyone seen failures of NM-B exposed to wet or damp locations with a higher failure rate than any THWN conductors exposed to the same?

 

[GoldDigger]

I do not think that the UL specs for those wire types say anything directly about requiring a nylon over jacket. That is there for mechanical protection and to meet durability criteria rather than as insulation per se. It is but one way to skin a THHN cat.
In earlier threads the consensus seemed to be that the conductors in NM-B may well meet the THHN or THHN-2 specification but if they are not marked as such they cannot be stripped out of the NM sheath and used that way.
Different manufacturers may use different formulations and specify and/or mark the inside conductors differently.

 

[A/A Fuel GTX]

Hey Augie, just for sake of gettin everybody in a uproar could you also tell us what the specs are for THHN insulation and THWN insulation, do they in fact specify 90* thermoplastic polyvinyl chloride with nylon jacket type insulation?
And if so, the conductors in NM-B cable are in fact the same even though the cable is not listed for use in wet location.
Next question, has anyone seen failures of NM-B exposed to wet or damp locations with a higher failure rate than any THWN conductors exposed to the same?

The major issue with NM-B in damp/wet locations is the paper insulation under the outer jacket that wicks water like a sponge.

 

[big john]

From the UL listing, the conductors are basically either unlabeled THHN or TW depending on whether there's a nylon sheath:

6.1 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 25.18) 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)...

 

[fmtjfw]

I do not think that the UL specs for those wire types say anything directly about requiring a nylon over jacket. That is there for mechanical protection and to meet durability criteria rather than as insulation per se. It is but one way to skin a THHN cat.
In earlier threads the consensus seemed to be that the conductors in NM-B may well meet the THHN or THHN-2 specification but if they are not marked as such they cannot be stripped out of the NM sheath and used that way.
Different manufacturers may use different formulations and specify and/or mark the inside conductors differently.

The N in TxxN means nylon jacket.