Bob ) said...

I've seen it done a lot, so I don't think there's anything in the code about
it. Maybe another poster knows. I've also seen where the same duplex
receptacle is on two circuits. I don't know if it's code, but most duplex
receptacles have a tab you can break off between the top and bottom. If
you're going to be pulling about 15 amps on a 20 amp breaker, you might want
to split that load also.

That is called a "split" outlet, but it is not powered by TWO circuits,
it is powered by a ONE double pole circuit. The circuit would use 14/3
(for 15 A) or 12/3 (for 20 A) cable providing a neutral that is common
to both halves of the outlet, while the other two conductors (red and
black) each connect to a different line from the double-pole breaker.

The original poster asked about having two outlets in the same ganged
box and powering them from separate circuits. I prefer to avoid this,
but occasionally it is not possible, especially in retro work. I have a
light switch location that originally had a single switch that I have
since added a second switch that happens to be on a different circut.

It is common practice in commercial installations to clearly label any
box where power comes from more than one source with that information
(eg: "CAUTION: this box powered from multiple locations - breaker 14 and
17").

In residential installations where this has had to occur, I have never
had a problem with inspectors, and none have ever required labelling, but
I prefer to put a label (usually on the inside of the cover plate), just
in case any future work is not done by myself.

Regardless, whenever you have to work in an electrical box, make sure
ALL conductors have their power cut off (not just the conductors you
plan to work on!).

--
Calvin Henry-Cotnam
"Never ascribe to malice what can equally be explained by incompetence."
- Napoleon
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