While working a bathroom remodel I encountered an odd issue. The lights are on a 3-way setup with one switch at each end of a walk-through bathroom. Housing the switch at one end is single-gang box also being used as a junction for two other circuits --one feeding the GFCI receptacles in the bathroom, and a completely separate pass-through circuit to the hall. Needless to say, the box is overcrowded. The 3-way circuit and the GFCI circuit are powered using a single 4-wire cable that enters from the breaker panel, with one hot for the lights and one hot for the GFCI. Both circuits share the remaining single neutral and ground wires. All the neutral and ground wires in the home are connected to the same bus bar. This 4-wire cable enters with a second 4-wire cable that powers the hall circuit. Because the entire box shares the ground wire of the first cable, this second cable has two wires not being used. After much frustration, I eventually figured the voltage found in these unused wires was a phenomenon of magnetic induction (which I assume everybody agrees).
The phantom voltage on these two wires is as follows:
Wire A to ground is 68v
Wire B to ground is 47v
My question is regarding the phantom voltage of 115 between wires A and B, which matches the mains, except no current. [EDIT: I should have pointed out 68+47=115] Is this coincidence, and what useful information can this tell me? My gut is saying it has to do with opposing phases of the 220v mains but pffft, I don't know. Please pardon my wayward terminology, I'm not a formally trained electrician but I've read through this forum and it appears some of you will know what's happening here.
Thank you in advance, Handyman in Oregon who hates when he can't figure stuff out.