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Can a junction box be shared by wiring originated from two separate panels?

Can a junction box be shared by wiring originated from two separate panels?

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Old 04-12-18, 11:33 AM
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Can a junction box be shared by wiring originated from two separate panels?

share a common device box or junction box under the USA NEC?

The situation is this. The house was built in 1955. Whoever did the original electrical work love to use those double sided metal boxes. I mean a 4X4 metal box with open ends on BOTH sides, they are 3.5" deep with mounting tabs for mud rings on both sides (NO, these are not extension rings, they are truly dual facing boxes). He put them in everywhere he could so if I have one receptacle in a room, the adjacent room will have a receptacle in the same spot facing the opposite side. Everything is in EMT conduits.

So the two apartments have a common kitchen wall. I found that he used one of these double sided boxes in this kitchen wall for the range hood. So basically I have the range hoods from both apartments hard wired from this junction box.
Now the strange thing is, when I opened up the junction box, I learned that both hoods were powered by the same circuit. In other words, there is wiring in there from apartment A, but it's powering the range hoods for both apartment. I guess apartment B didn't pay for their electrical use of their hood for some time.

Even stranger, there are two conduits feeding this box, one from apartment A (obviously), the other one is empty, no conductor inside, and it leads to the panel for apartment B.

So obviously there has been modifications that happened over the years.

My question is, can I run a pair of new conductors from the panel to this double sided box, and wire this range hood for apartment B? If I do so, I will have conductors in the box from two distinct panels, is this allowed?
 
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Old 04-12-18, 11:43 AM
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Is this the only box that feeds both apartments ?

Having multiple circuits there is ok but from panels in different units could present a problem.
 
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Old 04-12-18, 12:19 PM
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Yes this is the only box that feeds both apartments.

the other dual facing boxes are all inside individual apartments, like one receptacle inside bedroom 1 and one in bedroom 2.

I would like to avoid having apartment A paying the electrical usage of apartment B's range hood, and I think the range hood (or possibly over the range microwave in the future) are supposed to be dedicated anyways.

but the easiest way to solve this is to pull new conductors from the panel of B to this box. The conduit is already there. But I have never seen or heard of two circuits from different panels coming into one junction box. I suspect there may be issues so I want to get educated on this.
 
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Old 04-12-18, 12:52 PM
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Two circuits from two panels is ok but two panels from two different tenants is the issue. I'm not sure on this one. Will have to look further.
 
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Old 04-12-18, 02:48 PM
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I can't quote a specific code, but it sure feels wrong to me. There just seems to be too much potential for accidental backfeed, not to mention significant confusion when that box needs to be made safe/locked out. As PJ said there could also be a potential tenant law problem.

It seems like it wouldn't be too big of a job to replace the 3.5" deep square box with two 1.5" deep boxes back-to-back.
 
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Old 04-13-18, 08:51 AM
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It feels wrong to me either, but sure would like to know a definitive answer.

The confusion point you raised is a good one, if I shut off the main breaker to apartment A, never would I expect hot wire from another apartment inside the box.

It will be close to impossible to remove the existing box, because I only have access to the box from one side. The other side is fully concealed behind a wood finished range hood cover.

From this side I can see the box was nailed in with probably 3" screws onto the wood studs from each end. From working on other boxes the nails were driven past the stud and they hammered flat the nail on the other side of the stud. Even if I can release the box on apartment A's side, I cannot get to the nails close to the stud face on apartment B's side. Plus it has one inch thick cement rock around the metal mud rings, so I will need to cut a larger opening to remove the mud rings on both sides to even get to the nail heads, or try to slide in a sawzall blade to cut the nails. Plus I am not sure the knock out hole positions on these old double sided boxes alivn with new KO holes on standard 4X4 boxes.

My better bet is to just cut a 4X4 hole adjacent to the existing box and mount a new box, and try and reconfigure the existing conduit (which is vacant) from apartment B to run to the new box. Then put a blank cover on the old box.
 
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Old 04-13-18, 01:03 PM
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I don't see why NEC-wise it would be an issue. Both circuits are from the same service entry, so you're not concerned about larger than normal voltage differentials.

I can't imagine tenant law would be an issue if they are actually wired to the correct tenant's panel/meter.

I agree, it's probably a bit complicated for shutting off power in a given junction box, but that's not a specific NEC issue. (Maybe more of an OSHA issue, but unlikely to be raised as an issue).


Granted, I don't have specific references to quote... more my own thoughts/interpretations.
 
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Old 04-13-18, 01:43 PM
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Not sure about code but I would leave a note in box telling that both circuits need to cut off to work i n box.
 
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