Romex cable

[WW]

What is the difference between NM and NMB romex cable? Code here now will not allow NM to be used. WW

[dpb]

Plain NM w/o any following designation is the old, original "Romex (tm)" that used fiber insulation and hence was dry-only application. NM-C followed w/ the plastic. NM is, for the most part, unavailable.

AFAIK, the "B" designation is for building application and is the nomenclature for the color-coded sheathing of white/yellow/etc. designed to aid in ensuring proper conductor size is used in appropriate circuits and making for easier/quicker verification during inspection.

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[RBM]

[Nate Nagel]

I'm pretty sure the main diff between NM and NM-B is the higher temp rating of the insulation used. 90C vs. 60C IIRC. (remember back in the day taking down light fixtures and having to keep heat shrink handy to cover up the wire ends where they crumbled when you flexed them?)

nate

[RBM]

[WW]

[gfretwell]

Nope, The "B" means it uses a 90c conductor, not really THHN but a similar construction. I doubt anyone here has ever seen NM-c. That is a NM cable listed for damp locations. If you look on any wire manufacturer's web page I have looked at NM-c ends up referring you to UF (a wet location cable). I suspect there is not enough of a market to make it generally available in the US. I have heard you can get NM-c in Canada but I don't know that for sure. A recent code change may make NM-c more common..