Bill writes:
Scott Lurndal wrote:

There is no such thing a "12-3 THHN".


Someone else wrote "pull 12-3 w/ground THHN". Is that more acceptable
(I understood what he was trying to tell me--2 hots, a common and a ground)?


When wire is referred to with a hyphen (e.g. 12-3), that means that there are
three AWG12 conductors encased in an outer jacket. Typically, such cables
are type "NM" (non-metallic sheathed) or "UF" (underground feeder). w/G adds
a non-jacketed conductor in the outer jacket that is designated the grounding
conductor. Most XX-3 w/g cables include red, black, white and unjacketed
conductors.

THHN is a wire "type" code used for single conductors that are routed typically
through some form of chase (electrometallic tubing (EMT) or nonmetallic tubing,
wiremold raceway, etc.).

THHN may not be used without an enclosing raceway of some form (note that if
your light fixtures are mounted end-to-end and there is a nipple or length of
EMT connecting them, then the fixtures themselves become a raceway and THHN is allowed
from the head fixture through the rest in the row).

scott