Three-conductor cable for whole house

I inspected a home that had three-conductor cables throughout all of the electrical system. Usually I see two-conductor cables for 120 outlets and three-conductor cables are just used for the dryer, stove, and water heater. Does anyone see anything wrong with three-conductor cables being used for all electric needs in the home? The home was built in 2006.

I usually see them for 240V appliances, kitchen split plus and sometimes workshop but that should not be a problem. The missing tie-bars are though.

MWBC’s are perfectly acceptable, newer versions of the NEC require that the single pole CB’s have a handle tie or that a multi-pole CB is used.

And the famous two wires under a lug.

And your point is? You have stated quite a few times that this is not an issue in Ohio. Are you changing sides now?

I stated a fact. Never said right or wrong. That is up to each inspector to decide how they report it, if they report it.

Just incase I ever run into this??? I don’t understand the reasoning! Or how it even works since the red and black wire will end up at the same point even though they are on two separate breakers, can someone explain this to me! Are the wires going to a junction box and then ran different directions from there with 12/2 wire?

It’s a cheaper way of wiring, because they can run two 120V circuits from a single cable with 4 wires using a multiwire branch circuit, instead of running 2 separate cables with 3 wires each.

There are some unique characteristics to it. The red and black wires each serve a different set of devices or outlets, however they share the same grounded (white) conductor and equipment ground. Each of the ungrounded conductors (red and black) must be on separate phases. On a 120/240V system, they must have 240V potential between them to prevent overloading of the shared white conductor (with 240V potential between the ungrounded conductors, the grounded conductor will carry the difference in amperage rather than the sum of the two). Because the grounded conductor serves both breakers, it’s unsafe to work on either circuit unless both are deenergized, which is why the two breakers are supposed to share a handle tie.


Nice description chuck. :sunglasses:

With the advent of AFCI circuit breakers and the handle tie rule (which I hate) MWBC’s in homes are a dying breed. If not for those two things I would still use them.


It early!
What is a MWBC ?
Multi wire branch circuits?

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What year did the NEC implement the handle tie rule?

Thanks for making this make sense to me, so then in Matthews photo the system should be reported on as a safety issue because of the breakers not tied together according to Robert. Also the breaker alignment would have to have the red and black wire breakers side by side to have handle ties which would also make the power supplied rooms side by side to each other because the 3/G wire would start out at the one spot and then feed 2 separate areas from there, sounds confusing but I believe I got it.

It gets more confusing when the multiwire circuit occurs among half size breakers. In the picture below the two ungrounded conductors must still be on two separate phases. So the red ungrounded conductor must share a grounded conductor with a black ungrounded conductor in an entirely separate (adjacent) breaker slot. This home was built in 94, before the handle tie rule, although I’m not sure exactly what year the rule changed?Cornshock001

210.4(B) first appeared in the 2008 NEC which covered all MWBC’s. There were two similar rules in earlier editions of the NEC which required simultaneous disconnect for multiple circuits one the same yoke (such as a duplex receptacle) and for office furniture partitions.

Thanks for the response. I would of thought is was earlier than that. 1999 NEC says:

210.4(b) Dwelling Units. In dwelling units, a multiwire branch
circuit supplying more than one device or equipment on the
same yoke shall be provided with a means to disconnect
simultaneously all ungrounded conductors at the panelboard
where the branch circuit originated.

That language persisted through 2005. 2008 says:

(B) Disconnecting Means. Each multiwire branch circuit
shall be provided with a means that will simultaneously
disconnect all ungrounded conductors at the point where
the branch circuit originates.

Although the language changed they seem to say the same thing. “disconnect simultaneously” or “simultaneously disconnect” Don’t have anything before 1999.

Money. Money. Money.

They’re similar but not the same. The pre-2008 language applied only when it fed two circuits on one yoke, like a duplex receptacle. 2008 expanded that to include all MWBC’s.

Thanks again, a good example of what happens if you don’t read all the words. To compound the confusion I found the following illustration in an NFPA publication (pre-2008). Proper illustration, just lacking the words “same yoke’”

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You save a few bucks on the cable & installation, but what happens to the connected equipment should you lose neutral :smiley: Would not have it in my house, not worth the risk, don’t like 'em.

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So I assume the slim breakers are always on the same phase, then?