My question concerns the insulation surrounding the individual conductors on romex nm cable. I understand that romex cannot go into pvc underground, but THHN can. Therefore the insulation on these two types of wire cannot be the same. I am being told that romex is in fact THHN, Thanks for any input.
romex insulation
- Thread starter WBgreen
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Actually THHN can not either, but THWN can and since it is usually dual rated, THHN/THWN this conductor can.
The key is that the conductors inside the jacket of NM are not identified/marked per article 310.11 and this means they can not be used in any other way than what is allowed per article 334.
Roger
The key is that the conductors inside the jacket of NM are not identified/marked per article 310.11 and this means they can not be used in any other way than what is allowed per article 334.
Roger
romex in p.v.c.
romex in p.v.c.
This seems to be one of those grey areas. Article 334.10 b.1 lists type nm cable permitted in damp and corrosive locations. On Romex packaging from Southwire they classify romex as being n.m.b. No where that i see in the code book of 2002 does it list n.m.b. The insulation is not stamped on the individual wires but certainly appears identical to thhn/thhw except for the plastic that cracks in cold weather anyway. Did I miss the boat on this one or is romex not classified as non-metallic cable? Can you tell me what insulation it is. Also I would have thought the big reason for not allowing romex underground in P.V.C. is for 240 Volt installations because of an unshielded ground .
romex in p.v.c.
This seems to be one of those grey areas. Article 334.10 b.1 lists type nm cable permitted in damp and corrosive locations. On Romex packaging from Southwire they classify romex as being n.m.b. No where that i see in the code book of 2002 does it list n.m.b. The insulation is not stamped on the individual wires but certainly appears identical to thhn/thhw except for the plastic that cracks in cold weather anyway. Did I miss the boat on this one or is romex not classified as non-metallic cable? Can you tell me what insulation it is. Also I would have thought the big reason for not allowing romex underground in P.V.C. is for 240 Volt installations because of an unshielded ground .
jhc1xh said:
Underground installations are wet locations even if the conductors are in a raceway.
jhc1xh said:
334.112 The insulated power conductors shall be one of the types listed in Table 310.13 that are suitable for branch circuit wiring or one that is identified for use in these cables. Conductor insulation shall be rated at 90?C (194?F).
But, it is not marked per 310.11 so it is not THHN/THWN and we have to go with 334.80.
334.80 Ampacity
The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The ampacity shall be in accordance with the 60?C (140?F) conductor temperature rating. The 90?C (194?F) rating shall be permitted to be used for ampacity derating purposes, provided the final derated ampacity does not exceed that for a 60?C (140?F) rated conductor. The ampacity of Types NM, NMC, and NMS cable installed in cable tray shall be determined in accordance with 392.11.
jhc1xh said:
No, you are right it is NM.
See abovejhc1xh said:
Has nothing to do with it.jhc1xh said:
BTW, welcome to the forum.
Roger
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- Location
- Logan, Utah
jhc1xh said:
Just to add to the great information that Roger has posted. NM-B is type NM cable, the suffix B denotes that the conductors within the cable are rated at 90 degrees. Take a look at the fpn to 334.112.
Chris
(P.S. welcome to the forum.
)
M. D.
Senior Member
Here is a link to an article worth reading ,..considering all the water problems so many are facing ,.. I also agree with all Roger has stated ,..and welcome
http://www.ul.com/tca/ec/october05.pdf
http://www.ul.com/tca/ec/october05.pdf
glene77is
Senior Member
- Location
- Memphis, TN
It all boils down to a previous thread from last year.
After several pages of NEC code cites,
one of the engineers said that the PAPER liner inside the jacket
conducted water back into the equipment, and drips.
Accordingly,
the physics rules,
and the NEC describes methods to avoid problems.
Take your pick,
but, do not put NM in a wet location.
After several pages of NEC code cites,
one of the engineers said that the PAPER liner inside the jacket
conducted water back into the equipment, and drips.
Accordingly,
the physics rules,
and the NEC describes methods to avoid problems.
Take your pick,
but, do not put NM in a wet location.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Okay so who is going to find out what the jacket of nm cable is rated. I talked to a salesman last year who insists it is 90C. I have inspectors here saying it is 75C, hence they are only allowing 3 cables through a hole where there isthermal insulation(art.334.80). I have called southwire again to no avail. I want documented proof and cannot seem to find it. Any help would be appreciated.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
RUWired said:
I appreciate the effort but where does it say the temp. rating of the jacket? I don't see that info.
APPLICATIONS
Southwire's Romex SIMpull ? Type NM-B (nonmetallic-sheathed cable) may be used for both exposed and concealed work
in normally dry locations at temperatures not to exceed 90?C (with ampacity limited to that for 60?C conductors) as specified in
the National Electrical Code 1in normally dry locations at temperatures not to exceed 90?C (with ampacity limited to that for 60?C conductors) as specified in
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
RUWired said:
I was thinking they were talking about the inside conductors but you may be correct-- I will present that info thanks.
Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
Dennis
In the PDF, in the paragraph titled CONSTRUCTION, the forth sentence.
"
In the PDF, in the paragraph titled CONSTRUCTION, the forth sentence.
"
Conductor insulation is 90?C-rated polyvinyl chloride (PVC), nylon jacketed."
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Pierre C Belarge said:
I know the conductor insulation is 90C, it's the nm covering I was concerned about. I believe the statement ruwired provided verifies that the entire assembly is 90C. Do you agree?
dcspector
Senior Member
- Location
- Burke, Virginia
roger said:
Roger I agree with that and "Glene77is" posted a possible theory and or intent. Which I have heard many times from others.
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