In article , Tara Lynn wrote:
I'm in the process of buying a house and the lower level is an
unfinished basement. There is NM cable drooping unsupported
under the joists to single bulb light fixtures. Naturally I want
to get this fixed as soon as possible. I've been told to just
staple the wire to the bottom of the joists, but I believe this
violates NEC 334.15(C). Even if it didn't, it would look awful
and possibly cause problems someday when I finish the basement.

Correct, that *is* a code violation. However, the code does explicitly permit
NM cable to be stapled to running boards that cross the joists. So wherever
you need to cross joists, nail a 1x4 to the joists and staple the cable to the
1x4. When the cable runs parallel to a joist, code permits (requires, in fact)
that it be fastened to the face of the joist.

So the solution is to drill holes in the joists and rewire.
However, there is a hot air duct (uninsulated) that runs parallel
to and between the joists that the wiring has to cross.

How should this be handled? Does NM cable have to protected from
the potentially hot duct? Should it be run in a conduit? How
should I route the cable around the duct?

A 1x4 across the joists solves *all* of those issues.