I have existing 1/2" emt conduit servicing 20 amp receptacles connected to a single pole 20 amp breaker. So there are 3 12G wires, 1 black, 1 white and 1 green in the existing conduit.
I'd like to add a single 240V 20 amp receptacle in a separate box at the end of this conduit run, by running black and red 12g wires back to a separate 20 amp double pole breaker. These wires will pass through unbroken through each box. Can I just mark the 2nd black wire with say, brown tape to keep it identified? Or does the 2nd black wire need to be a different color, say brown? Thanks!