I am concerned that the original post is getting a bit hi-jacked, so I will divide my responses into two posts. I can't resist a good piecework bashing, so it will follow. Perhaps the moderators will move the original post into a new thread; if so, this post should follow the grays/whites topic.
Sarge said:
so started to think (which is normally dangerous for me) if I used "high voltage" MC as my travelers and "low voltage" MC for my commans it might make it easier.
I don't know of the color configurations of the cable you're contemplating, so I can't really comment on this. I don't know how you can make it easier that way.
Perhaps simply looping your common around the travellers a few times would be an easier solution.
Sarge said:
the only problem I can forsee is that the "high voltage" MC has a GREY grounded and the "low voltage" has a WHITE grounded and I am not sure that the two can be mixed.
Trevor said:
It depends on what voltage systems you have within the building.
I somewhat agree with Trevor's response; see 200.6(D)(1) & (2). If there are two systems (120/208 and 277/480) in the same
raceway, enclosure or what have you, then one must be white and the other must be gray.
The idea of two systems in the same building, but not sharing a raceway, and having two colors for the same system in the same raceway is confusing as all get out, but would still be legal, IMO.