multi wire circuit

[John Dirks Jr]

I suspect this one might not pose a problem but I wanted to run it by the gang to get opinions.

As you can see, two hots from a 14/3 are on the same breaker (same phase). The breaker is listed for two conductors so no issue with double tap. Since both hot conductors are fed by the same 15amp breaker, the shared neutral for this multi wire circuit should not ever be overloaded since the combined currents of both hots would trip the breaker at anything above 15amps. Thus, the neutral would not be subjected to an overload. Am I thinking this through correctly? The label on the panel listed both hots as serving the living room. The way I see it, that really no different than having a single hot serving the entire living room.

I can't see a problem with this arrangement. Can any of you?

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[rkenney]

What makes you think a neutral is shared?

If it were, you need to consider what gauge wire is required for a 30 amp circuit (10). This is the wire gauge required for that neutral. The currents are additive because they share the same bus bar (1/2 phase).

So the current in both circuits 'hot' wire could be just under trip threshold for the breaker (say 14 A each) then the total current in a shared neutral is 28 Amps.

Ultimately it depends on how many devices are on each 'leg' of that breaker circuit. Beyond the scope of a home inspection.

[John Dirks Jr]

What makes you think a neutral is shared?

If it were, you need to consider what gauge wire is required for a 30 amp circuit (10). This is the wire gauge required for that neutral. The currents are additive because they share the same bus bar (1/2 phase).

So the current in both circuits 'hot' wire could be just under trip threshold for the breaker (say 14 A each) then the total current in a shared neutral is 28 Amps.

The two hots are using a single neutral. I traced it and verified it.

Now, think of it like this. In order for there to be 28 amps coming back on the neutral, there would have to be 28 amps flowing through that breaker (both hots are on the same breaker). Tell me how 28 amps is going to flow through that 15 amp breaker. It won't. The breaker will trip before the neutral is overloaded. It caught me at first but after I thought about it, I cant see a problem.

[inspector57]

You are correct in your thinking, the neutral will only "see" the amount of the combined amperage, in this case the limiting factor is the one 15 amp breaker.

If it were on different breakers on the same phase then you could see 30 amps on the neutral.

[Marc]

...The two hots are using a single neutral. I traced it and verified it...

In that case, the only issue I see is that the two breakers serving the MW circuit do not have a common handle.

Did you confirm that the two hots are on separate poles? They should be.

I'm not understanding Bob K, not that I need to.

Marc

[John Kogel]

John, you are correct, if the red and black both use the one neutral, the current on the neutral will never exceed 15 amps.

But it is an amateur installation, so you could be justified in calling it out for a closer look.

I can't figure out a reason for what he did there.

[Carson2006]

Mr. Dirks, this is not a multi-wire branch circuit. The two ungrounded (hots) have no voltage between them. While it's an odd connection, depending upon how the circuit is installed, there is nothing wrong with it and nothing unsafe; as far as the picture goes. Two wires from the same hot leg on a listed two wire termination circuit breaker is no different than connecting (wire-nutting) a wire in a splice/junction box. IMHO it is nothing you should call out. Additionally, in a true multi-wire branch circuit (shared neutral) the neutral current will actually be lower than that of separate branch circuit neutrals and not the sum of the currents from each branch circuit. Therefore the neutral doesn't have to be larger than the branch circuit "hots".

[John Dirks Jr]

For the record, the report was delivered before I started this thread. I did not write it up. Initially, when I first removed the cover I thought it was an issue. But when I realized it was the same breaker, I backed off.

In any case, I would rather issue an addendum than a correction to a report. In this case, I didn't have too.

[Jim Katen]

It's not a multi-wire circuit, but I have little doubt that the installer intended for it to be one. It's also possible that it was one and got rearranged by an amateur.

If I were inspecting the house, I'd suggest having an electrician re-wire it to restore the multi-wire circuit.

[Garet]

Goofy electrical issues (...and this is one of them) are the work of someone who didn't understand the systems they were working. Given the hidden nature of electrical systems, that means there are likely other issues you're not seeing. It's time for Sparky to pay a visit.