Shared Neutral problem? & Can ground be shared?

Old 02-14-04, 12:09 PM
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Question Shared Neutral problem? & Can ground be shared?

I'm replacing some old wiring in my house and have happened upon a few scenarios where I need some advice.

Shared Neutral
In a couple of places I have found that 2 different circuits (of the same Amp) share a neutral in an unusual way to me.

In one case, circuit 1 splits into two branches that I'll call 1a & 1b. Only the hot wire for circuit 1b continues to a junction box that is shared with circuit 2. At that point, circuit 1b shares a neutral with circuit 2. So basically circuit 1 has one path for the hot wire back to the circuit breaker, but two different paths for the neutral depending on whether you are on 1a or 1b.

In another case, circuits 3 & 4 share a neutral initially. They split at a junction box that also contains circuits 5 & 6. At this point, circuit 5 shares the neutral from circuit 3, but circuit 4 is connected to the neutral from circuit 6. (I may have not articulated this one correctly, but you get the idea.)

Is this acceptable? At a minimum is certainly makes it harder to figure out the circuits.

Shared Ground
The house has conduit (EMT) and was originally grounded thru each box. As I'm replacing wire there will be a few areas where it will be difficult to run a new ground wire. In these instances, can I share a ground wire between 2 circuits of the same Amp? In one case, the circuit that I want to do this is a branch circuit off of an existing circuit that will share a ground wire with a different circuit w/ground wire.

Ok, I have one more question. An electrician installed a new circuit for my new central A/C. In one area with not much room to work, the wire (NM-B 10/2) is not secured and lies on the copper hot water pipe coming out of my water heater. Will the heat from the pipe cause any damage to the wire? Should I be concerned about this?

Old 02-14-04, 05:44 PM
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Shared neutrals are very safe under the right condiions, and very dangerous under the wrong conditions. Do you have reasons to believe that this might be improper? If so, we can pursue this. Start by telling us what brand your panel is (e.g., SquareD) and then identify all of the circuits you mentioned with the actual circuit numbers (i.e., the number embossed into the panel cover).

It is okay to share a grounding conductor between two circuits.

The sheathing on modern cable can handle heat up to 90 degrees C. The water from your water heater is less than this, probably not more than 60 degrees C. Nevertheless, I'd move the cable so that it is not in direct contact with the pipe.
Old 02-14-04, 07:16 PM
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The circuit must use the neutral (or grounded conductor) that is together with the hot conductor. The current shouldn't be traveling back to the panel in a different cable/conduit.
It will functionally work but not a good idea for conductor/cable heating.

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