I am selling some surplus cable on Craigslist.
One guy asked me if it was NMB, as NM doesn't meet code.
Well, yeah, it is NMB; but why wouldn't NM meet code? It is only good up to
60 degrees, but all small circuits have to be 60 degrees anyhow, so why
would it matter?
I don't know whether code requires NMB for all circuits now, but it's
typically required within 12" of light fixtures. I've seen plenty of
regular NM cables above light fixtures where the insulation has gotten hot
and crumbled away, leaving bare wires. Scary.
As far as I know, the only difference between NM and NMB is the higher
temperature rating on NMB insulation. The conductor is the same size, so I
don't think it would make any difference, except around lights. You could
always put a junction box in the attic with a short run of NMB to connect
to the main NM line.
I probably wouldn't use NM if I were wiring a new house, but it would
probably work fine for wiring in a garage, shed, or minor repair projects.
The NEC now requires the insulation on NM wire to be 90 degrees. I think
the major rationale for a 90 degree rating is Romex is installed in
building insulation. (If you had old stock, it is up to the "authority
having jurisdiction" whether it could be used.)
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