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How do I connect old 2-conductor circuits into modern 3-conductor wiring (with third wire ground)?
I'm moving an electrical junction box that was installed by an electrician. Generally I assume an electrician does things right, but I'm suspicious about something he did in this box I'm moving.
The box has modern 3-conductor (NMB 12-2 Romex, which is 2-wire plus a third wire bare dedicated ground) run to it from the circuit breaker. The box junctions this with an old circuit that is two conductor with no ground.
The way the electrician did this was to tie the white (neutral) wire in the old 2-conductor cable to both the white (neutral) and bare (ground) wires in the new 3-conductor. Obviously, black (hot) was tied to black.
Now, I would have thought to dead-end the third wire (bare ground) to the (metal) box, and to just connect black to black and white to white. I thought you weren't supposed to connect dedicated third-wire ground with the neutral return wire, even though they're both grounded eventually. What should be done in this situation?
You need to take the ground wire off the neutral wire connection in the junction box. The big problem is, you now have parallel wires carrying the neutral current back to the panel. Anyone disconnecting that ground wire in the panel could get electrocuted, not knowing it is carrying current. The ground wire should never carry current except to clear a ground fault (short circuit). You are correct to dead end the ground wire at the junction box. The rest of the circuit will simply be a two wire circuit with no ground, as it is now. Good catch.
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