cableswiring
Planning to use Legrand Wiremold 700 Series Metal Surface Raceway.
Couple questions:
There is nothing in Code that says that a metal box can't be part of the fault current path -- this is done all the time in systems that use AC, MCI-A, or metal conduit. (Personally, I'd use a self-grounding receptacle to save the ground clip and pigtail for neatness' sake, even though it doesn't get scored against box fill.)
If you are curious, btw, look up NEC section 250.148.
So I cut the diagram out of the PDF instructions
The reason for the red and yellow is that this is really two switches. The yellow is for your light and the red is for your fan. There's two for each, should you want to 3-way both.
The catch here is not the 3-way setup, but how you will get two hots to the box. You need one hot for the light, one for the switch and your neutral. Assuming you do, you'll take the yellow wires and attach them to the white and red that the previous 3-way used.
Best Answer
It can take its ground either from the underlying box or from a pigtail
From the installation instructions Legrand provides on their website for the 500/700 series products, I don't see any reference to an explicit grounding screw being driven, so it appears that it picks up its grounding from the underlying box being grounded. If that's not possible, the bump at the top-left that doesn't have a mounting hole in the cover corresponding to it should be tapped to accept a 10-32 grounding screw and corresponding pigtail.
...but always uses individual wires
Surface raceways are designed to be used with individual THHN wires, just like their conduit brethren. Furthermore, you have to obey the fill chart provided by the raceway manufacturer; if what you plan to run isn't a combination that's on the fill chart, you can't run it, as the irregular shapes of surface raceways mean that normal conduit fill calcs can't be used and the provisions of NEC 386.21 and the first paragraph of 386.22 apply instead: