I'm rewiring my garage from in my opinion is an odd setup.
In my house panel (200A split phase) there is a 20A breaker there is a junction somewhere ( I haven't traced it out yet which branches this circuit to two. The net result is a 3 way switch for the garage lighting and an always hot circuit. I haven't quite figured out how this is done with three wires. Both circuits are run over 3 conductor overhead wiring to the garage. At the service drop, the cable is connected to two 12/2 cables. The neutral is shared, grounds are tied together and just left hanging there at the drop.
Not liking this setup at all I worked backward and wired up all the new stuff in the garage to a small secondary panel. The next step is to connect to the existing wiring, but I'm trying to figure out what the previous guy did. The voltages to the wires coming in are strange. I'm pretty certain this is partially because they are not grounded. This brings me to my first question.
I've done lots of work inside homes but never from building to building. Since overhead cable doesn't have a ground, and neutrals and grounds are generally on the same bus within the breaker panel, this this mean I should have a grounding rod at both ends of this cable?
The other question I'm sure I can figure out. I haven't closely examined the previous guys work other than at the service drop. Since the voltages are so strange it's difficult to tell what is going on. If someone has a quick answer, I would appreciate it. Like I said the garage lighting can be controlled from my kitchen and a switch in the garage. How did they wire a three way switch in addition to a always hot switch on three wires.
Best Answer
The sub panel will need the ground to be separated from the neutral. The only place they are joined is inside the main breaker panel. This prevents open neutrals between the main and sub panel from sending current over the ground, and possibly electrocuting someone if a better path to ground can be found.
For the 3 way switch, I'm guessing you need to trace more wires, or you have a smart switch of some kind. You'll need to check the switches first, and then start tracing the cables on each end to see where they go. I'm guessing a second line is running just for the 3 way switch that you haven't found.