Typically, a multi-wire circuit run has two hots on separate legs, a shared neutral and a shared ground. There are very specific rules (NEC 210.4) about these types of circuits to ensure that the neutral does not become overloaded (if the hots are accidentally place on the same phase) among other considerations.

Given that many locations now require arc-fault circuit breakers, which require dedicated neutrals anyway, running two circuits in one piece of Romex would take five conductors, and only the ground would be shared.

In this case, is the run still considered a multi-wire circuit for NEC purposes?

For example:

Do both hots have to be on separate legs since there are dedicated neutrals? Do they need to be on a two-pole breaker with a single pull so both hots are powered on at the same time?

If they are not considered multi-wire, are there any other specific rules that apply to these?

(NEC 2014 is relevant in my jurisdiction).

up vote 9 down vote accepted

In this case, is the run still considered a multi-wire circuit for NEC purposes?

Short answer: No

Here is the relevant Code definition:

Branch Circuit, Multiwire. A branch circuit that consists of two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system.

Since you would have two hots and two neutrals they are now separate branch circuits. They do not have to be on a two pole breaker or have a handle tie since they do not share a neutral. They do not have to be on opposing hot legs, they can both be on the black (left) or red (right) feeder bus.

Good luck and stay safe!

  • Can you add the Article and section number for the code definition? I'm not finding it by searching for the text. – Nick Oct 2 '17 at 11:32
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    Article 100. Most definitions are in Article 100 unless they are specific to that Article then they are found at the dot2 locations of the Article e.g. 517.2 – ArchonOSX Oct 2 '17 at 11:36

They do not need to be on opposite poles, as that would not change the amount of current flowing on the fully separated neutrals.

There is no earthly reason to require common-trip or common maintenance shutoff (the latter being the requirement for an MWBC).

You're simply talking about a wiring method.

How would you run two separate (non-MWBC) circuits in the conduit wiring method? Run black and white for circuit 1, and red and white-red for circuit 2. Steel EMT pipe is your shared ground. Very routine.

Change the steel jacket to plastic with a ground wire, and nothing changes electrically. It's still two separate circuits.

No more than four

However, EMT and Romex have the same fill rules. No more than four circuits in a confined channel.** You've probably seen this rule expressed as "no more than four" Romex cables tightly together, on the same bundle, clip or staple.

Here's the gotcha. Your two complete circuits in your /2/2 cable count as two. This was the advantage to Multi-Wire Branch Circuits: they only count as one circuit, so you could get 4 MWBCs or 8 useful "circuits" in the same channel, conduit or raceway. Now you are down to two /2/2 cables and 4 useful circuits.

**There's a lot of complicated wire-counting involved, but when you're working in single-phase power (including split-phase), it always works out that a single circuit is 2 of the conductors which are "counted". Neutral wires in 120-240 and in MWBCs do not count.

  • The "No more than four" rule of thumb (not NEC rule to my knowledge) is because of the required wire ampacity derating for parallel conductors in Table 310.15(B)(3)(a) drops the useful voltage for 90 degree conductors below that required for the highest rated circuit breaker for 14-gauge and 12-gauge circuits. You could run more than 4 circuits with 90 degree conductors in parallel with 12-gauge wire (up to 10 circuits), but then you're limited to a 15-amp circuit breaker for each of those 12-gauge wires--basically a waste of money for thicker wire, but still allowed by the NEC. – statueuphemism Oct 2 '17 at 15:51
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    @statueuphemism yeah, I started going into those gory details, but soon realized it would add a lot of unnecessary bulk and accomplish nothing. "No more than four" isn't stated literally in code, but it is positively derived from Code, much of which you have outlined. Call it a rule of thumb if you like, but I'm unaware of there being any wiggle room. I'd sure like to know. – Harper Oct 2 '17 at 16:26
  • I called it a rule of thumb because you're allowed to run more circuits in parallel, but it almost never makes financial sense to do so because of the requirement to derate the wire and adding some space between cables/raceways is usually more cost-effective. We agree though, there is no wiggle room that you would have to derate the breaker at more than 4 circuits closely run in parallel. – statueuphemism Oct 2 '17 at 16:33
  • Yeah, I've contemplated upsizing and taking the derate, but it's not fun going out and buying abnormal sizes of wire (I like my multicolors) and you soon run into the other conduit fill issue, only so many #10s allowed or pullable. – Harper Oct 2 '17 at 16:42
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    @Ed I don't think we are talking about receptacles. – Harper Oct 2 '17 at 20:09

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