NM Cable (Romex wire)

[chris1971]

Just curious, when did the insulation on the conductors of NM become 90 degree C and THHN?

 

[Cavie]

Just curious, when did the insulation on the conductors of NM become 90 degree C and THHN?

It hasen't. You must use the 60 degree coloum

 

[chris1971]

I understand that. But the individual conductors are THHN. When did the individual conductors become THHN. I see older romex with thicker insulation on the individual conductors. Just curious.

 

[M. D.]

 

[bradleyelectric]

I believe it was '86. Don't overlook the fact that when it became NM-B a lot of the insulation was thick. A certain insulation manufacturer developed a 90* insulation and as is the way it happens with the code making panel it was accepted that a 90* insulation would be more safe. The other manufacturers increased the thickness of there insulation to meet this requirement.

 

[chris1971]

So basically romex installed from 1986 on is rated at 90 degree C? It would be safe to install a dimmer with this type of wiring? The dimmer states the wiring must be rated fo 90 degree C.

 

[480sparky]

1984, not 1986. There was no Code issued in '86.

I understand that. But the individual conductors are THHN. When did the individual conductors become THHN. I see older romex with thicker insulation on the individual conductors. Just curious.

The conductors in NM are simply required to be a 90?C insulation, not necessarily THHN. Truth is, you can't even prove they are or aren't THHN as they are not marked.

So basically romex installed from 1986 on is rated at 90 degree C? It would be safe to install a dimmer with this type of wiring? The dimmer states the wiring must be rated fo 90 degree C.

One would think, but that would be an assumption, at least for knowing the installation dates to the late 80s.

 

[Volta]

I understand that. But the individual conductors are THHN. When did the individual conductors become THHN. I see older romex with thicker insulation on the individual conductors. Just curious.

They are rated at 90 d C. They are not officially THHN, however. They may have similar construction, but are not rated as a recognized wire when some portion is not still within the sheath.

 

[LarryFine]

Well said.

 

[nakulak]

 

[480sparky]

 

[infinity]

The oldest NEC code book that I have is 1987 and it states:

336-26. Conductors. The insulated conductors shall be one of the types listed in Table 310-13 which is suitable for branch-circuit wiring or one which is identified for use in these cables.
Conductors shall be rated at 90 degrees C. The ampacity of NM and NMC cable shall be that of 60 degrees C and shall comply with 310-15.

 

[M. D.]

Igot the sense that my first post did not read properly ,. just incase here is the link

Use of Type NM-B Cable for Wiring of Residential Lighting Fixtures

 

[hardworkingstiff]

I can't prove it (and my mind is not as good as it once was) but I though I saw NM-B in the 70's, not emphactic about it, just that's what my gut says.

 

[hardworkingstiff]

duh again

duh again

In the mid-1980?s, the outer jacked of this cable changed from an impregnated, braided covering to polyvinyl chloride (PVC), and the internal conductor insulation went from a 60[FONT=WP MathA,WP MathA]E[/FONT]C to a 90[FONT=WP MathA,WP MathA]E[/FONT]C rating. This newer cable is typically referred to as Type NM-B.

http://www.eijatc.org/includes/newsletterFiles/spring06.pdf

 

[480sparky]

The oldest NEC code book that I have is 1987 and it states:

1981:

336-2 Construction. Conductors of Types NM and NMC shall be one of the types listed in Table 310-13 which is suitable for branch-circuit wiring or one which is identified for use in these cables. The ampacity of Types NM and NMC cable shall be that of 60?C (140?F) conductors in Table 310-16.

1984: (Red highlight is mine)

336-2 Construction. Conductors of Types NM and NMC shall be one of the types listed in Table 310-13 which is suitable for branch-circuit wiring or one which is identified for use in these cables. Conductors shall be rated at 90?FC (190?F). The ampacity of Types NM and NMC cable shall be that of 60?C (140?F) conductors in Table 310-16.

It is strange that my '84 does not have the vertical bar along the margin indicating the change.

 

[LarryFine]

It is strange that my '84 does not have the vertical bar along the margin indicating the change.

You could always add one.

 

[Len]

90c

90c

you can install dimmer with romex.
Romex is rated for 90c but you have to use 60c column for ampacity...
Only over 100amps and larger than #4 can you use 75C rating.....