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Old 05-13-2010, 01:45 PM   #1
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Nm-b & nm-c ?


What is the difference between NM-B and NM-C cable? Is NM-C still manufactured?

Thank you.
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Old 05-13-2010, 03:01 PM   #2
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For NM-B

"
Inner conductors are type THHN, rated 90 degrees Celsius, 600 volts. Solid strands. Outer jacket is PVC rated at 75 degrees Celsius. Amapcity of the product is limited to that for 60 degrees Celsius
"

This is about as clear as mud. It does imply that the heat flows from inside to outside but that's not news.

NM-C may be corrosion resistant.

Last edited by Yoyizit; 05-13-2010 at 04:01 PM.
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Old 05-13-2010, 05:07 PM   #3
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The types are actually NM-B and NMC-B, where the -B suffix designates that the conductors have 90C insulation.

The difference between NM and NMC seems to be that NMC is additionally rated for moist, damp, and corrosive locations.

From UL 719, Nonmetallic-sheathed cables. http://ulstandardsinfonet.ul.com/scopes/0719.html
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Old 05-13-2010, 08:21 PM   #4
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Quote:
Originally Posted by McSteve View Post
The types are actually NM-B and NMC-B, where the -B suffix designates that the conductors have 90C insulation.

The difference between NM and NMC seems to be that NMC is additionally rated for moist, damp, and corrosive locations.

From UL 719, Nonmetallic-sheathed cables. http://ulstandardsinfonet.ul.com/scopes/0719.html
Do you know if the outer jacket is colored the same as NM-B? i.e. 14 is white, 12 is yellow and 10 is orange.

Thank you,
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Old 05-13-2010, 09:00 PM   #5
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NMC was meant for damp locations. It had a sheath similar to UF cable where the cable jacket surrounded the conductors. It is wasn't meant to be buried in the ground, nor is it sunlight resistant. I haven't seen any NMC that is any newer than maybe the '60s-70s, but it's still in the codebook.

If something like it is needed today, UF-B is used. UF cable can be buried directly in the ground and is approved for wet locations. It can also be used anywhere NM-B can be used, although I don't know why you would want to. (hard to strip)

NM-B is your modern normal indoor wire, what most people call "Romex" Which was /is a brand name. Yes it is made in different colors, so the inspector can see you used 12 awg to wire the kitchen and bath (for example) instead of reading the sheath.
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