I have a stud cavity through which I need to run some signal wiring that's sensitive to ingress noise. An industry-standard recommendation is to run the wiring in properly bonded metal conduit (raceway, per the NEC, right?).
There are plenty of 110V metal junction boxes in the same stud cavity. However, I can't mix signal and control wiring in the same junction box (or compartment of the junction box) with 110V wiring. Nor can I put it in the same raceway, right?
Supposing that I run new RMC and metal junction boxes for the signal wiring, how should I bond the boxes (or at least one box if the RMC provides electrical continuity to the other)? Do I use a bonding jumper from the signal wire box to one of the 110V boxes?
The signal wires are going to be electrically isolated from the boxes (i.e. they pass through brush plates and aren't terminated at the boxes).
Best Answer
You probably don't need to go full RMC; cheaper EMT and plain stamped handy-boxes will do. Both types of conduit are acceptable as grounding paths for 200A++ of fault current, your milliamps of signal noise will be handled with ease. I never run ground wires inside EMT.
If you have a section of Conduit isolated from mains grounding, grounding it is simplicity itself. There should be a hole in the back of the box tapped #10-32. You simply put a 10-32 screw in there, shepherd's hook a 12AWG solid pigtail to it, and wirenut that to your grounding wire, any color you like as long as it's green, yellow/green or bare.
Then you exit the wire through a cable clamp or grommet, which fits in a standard knockout.
Then you run the wire in-wall to whichever ground point you deem appropriate. If you'd like guidance on that, look at the NEC rules for retrofitting ground.