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Multiwire Circuit ... what would you do?


StevenT
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During a recent inspection of a panel, I noticed two multicircuit conductors that shared a neutral in a common conduit, connected to two separated single pole breakers. As they were not next to each, I checked to see that they were not on the same bus.

I understand that multicircuit conductors that supply devices that do not have a common yoke or strap do not have to connect to breakers that are tied together, so I attempted to trace it's destination in order to determine such.

Of course, the panel was not properly marked, extremely crowded, and the basement was a maze of bx and emt, exposed, hidden, and abandoned.

I found a box where the circuits split to separate locations. I felt satisfied that the installation was acceptable.

I feel that the required actions that I had to take were borderline of being exhaustive, especially since portions of the run were hidden and buried in ceilings.

My question is; At what point should I simply have put it off to have the system checked by a "qualified electrician"?

Now that it's done, I'm glad that I didn't make that call. Besides the added expense to my client, I think I would have been embarrassed when the electrician would have said..."there's nothing wrong with it"

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I would punt. Never go beyond your abilities. If you do not know or do not understand an installtion then explain that this goes beyond your training to evaulate the system. Explain the technical issues and that this a unique product ot non-standard installation. Let them know there is a possibilty that nothing is wrong but for thier safety you recommend a professional opinion. I believe people will respect you for your honesty and turn a bad situation into a sales oppurtunity.

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Originally posted by StevenT

During a recent inspection of a panel, I noticed two multicircuit conductors that shared a neutral in a common conduit, connected to two separated single pole breakers. As they were not next to each, I checked to see that they were not on the same bus.

So far, so good.

I understand that multicircuit conductors that supply devices that do not have a common yoke or strap do not have to connect to breakers that are tied together, so I attempted to trace it's destination in order to determine such.

Of course, the panel was not properly marked, extremely crowded, and the basement was a maze of bx and emt, exposed, hidden, and abandoned.

I found a box where the circuits split to separate locations. I felt satisfied that the installation was acceptable.

I don't understand. You should have been able to tell if the two parts of the circuit were fed from different poles just from what was going on inside the panel. Or was there more than one MW circuit in the conduit?

I feel that the required actions that I had to take were borderline of being exhaustive, especially since portions of the run were hidden and buried in ceilings.

My question is; At what point should I simply have put it off to have the system checked by a "qualified electrician"?

Now that it's done, I'm glad that I didn't make that call. Besides the added expense to my client, I think I would have been embarrassed when the electrician would have said..."there's nothing wrong with it"

Only you can make that call. You seem to have a very good understanding of MW circuits. I think you did the right thing.

If the interior of the enclosure is a tangled mess, I carefully grasp one of the wires and gently wiggle it up & down. Usually, I can then see the other end moving beyond the tangle. This helps me to determine if the MW circuit is properly fed. I like to be sure of this. However, there's always the danger that, as I wiggle the wire, there'll be a fizz, spark, arc or boom. It's a calculated risk. Each inspector has to make the decision for himself or herself.

Just to be clear. MW circuits aren't non-standard. In commercial wiring, they're the norm. Occasionally, in my area, we have houses with a half dozen, or more, MW circuits.

- Jim Katen, Oregon

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I have wired plenty of shared neutral circuits but always on a commercial or industrial job. They are great circuits. However, I am not a fan of running shared neutrals in residential homes, never have and never will. Give me metal conduit and separate conductors and I am happy.

Although this is my opinion on shared neutrals, it is not the law and I see it done in residential once in awhile.

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Originally posted by BlackJack

Is it not true, that without a handle tie, it is non-standard and a safety problem?

No. The only time you need a handle tie is when both of the circuits supply devices on the same yoke. For instance, in residential wiring, electricians will sometimes run a MW circuit to a duplex outlet to power a dishwasher and a disposal. In that case, because both halves of the duplex are connected to the same yoke, there should be a handle tie between the breakers.

Read all about it in section 210.4.

Look inside a commercial panel and chances are you'll see dozens of MW circuits wired to un-tied breakers.

- Jim Katen, Oregon

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Locating where the circuits originated was not a problem (grasp and wiggle), locating where they terminated was a different story. I would have felt better had they originated at breakers that were tied together (that would have been easy).

Although I have been involved in many different aspects of construction, and know "a little bit about alot of things", I am relatively new as a home inspector. I see that my limited knowledge can be dangerous, and I must learn "alot about alot of things".

The most important lesson I learned was to "confirm what I think I see" and "think I know".

Looking back on what transpired, I am relieved that I invested the extra 20 minutes to trace the circuits and another 10 minutes confirming how multiple conductor circuits can and cannot be wired. Rather than taking a "quick" look and incorrectly calling in an uneeded "expert".

I feel that there are many different reputations that I can build as a H.I., and I realize that occaisionally, I will make that mistake, I prefer it be when dealing with unfamiar "oddball" systems or rare techniques. I do not feel that multiple conductor circuits is one.

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