I have two 1/2" EMT conduits that run from one end of the house to the other end, over a distance of about 50 feet. The two conduits run more or less in tandem close to each other until it gets to the rear of the house where they enter the same junction box, then one exits to the laundry room and the other turns to a attached shed. In each conduit are two 20A circuits, four conductors, two hot and two neutral. Looking at the junction box in the rear, and looking at the panel in the front of the house... conduit 1: circuits 8A, 8B conduit 2: circuits 12A, 12B If I move circuit 8B to 6B, and 12B to 10B, both of these circuits would be on opposite legs, I can put in handle ties to the breakers, so now 6B and 8A can share one neutral, 10B and 12A can share one neutral. I would end up freeing up one neutral conductor in each of the two conduits. In the rear where the two conduits enter the same junction box, can I take the extra unused neutral conductor, one from each conduit, and use it as a pair for a new circuit? Or is there some code that says conductors for the same circuit must be housed in the same raceway?

I would like to replace some two prong outlets with 3 prong outlets. The outlet boxes are metal and I was planing on using them as a path for the ground wire. When I tested the outlet the readings are hot to neutral 119v, neutral to box .4v and hot to box 24v. I realize I cannot use the box for ground but can anyone tell me what this might mean?