Multi wire branch circuit NM cable

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Jpflex said:
But couldn’t this be done incorrect by taking a multi-wire nm cable such as 12-3 with ground and wire the line leads to depot are breakers on the same phase and share a neutral.
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Yes it could but there a difference between what you're calling a "multi-wire nm cable such as 12-3 with ground" and a true MWBC.
 
infinity said:
Yes it could but there a difference between what you're calling a "multi-wire nm cable such as 12-3 with ground" and a true MWBC.
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I thought 12-3 nm cable was used for multi wire branch circuits or travelers for 3 way switches?
 
Jpflex said:
I thought 12-3 nm cable was used for multi wire branch circuits or travelers for 3 way switches?
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It certainly can be as well as other 3 wire cables...It all depends on how it's terminated.
A 3 wire cable is simply that.... it can be used for a MWBC, travler circuit, 240/120 circuit, 3 phase circuit, etc.
 
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Jpflex said:
So lines per circuit would have to be on different phases such as A and B for current not to be doubled on neutral?
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Look at any 120/240 feed from the power company's transformer. Three wires, two hots and one neutral. The neutral is not bigger than the phase conductors. (y)

Of course the power company knows they did not put both phase conductors on the same phase!;)

Back in the old days I would run MWBC with 12/3 NM in lots of cases. Of course I never envisioned someone screwing with the breaker locations later and not noticing the two phase wires going into the same NM cable!:eek:
 
Jpflex said:
Then what does a true mwbc cable look like?
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There is no such animal as a specific "MWBC" cable.
MWBCs are conductors of any type (cables, individual conductors, ect) connected in a manner than makes the circuit a MWBC>
 
Sberry said:
Got to be careful on some older gensets and welding machines. They have 120 outlets and they have 240 and that is not the same as a 120/240. They are not made to hook up to premise power.
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My Lincoln SA-200 Pipeliner is great at releasing the magic smoke from stuff when people don't listen to me
 
Jpflex said:
Then what does a true mwbc cable look like?
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A MWBC wiring will have a single neutral accompanied by more than one ungrounded conductor. In a cable assembly it could be any #/3 or #/4 (ie 12/3 or 12/4)
A 12 or 14/2/2 would not constitute a cable needed or used in a MWBC condition as it has 2 neutrals and 2 ungrounded conductors. This cable was designed to accommodate the simplified single pull for 2 circuits (similar use reasoning as a 12/3 in this case) and useful with an AFCI as most mfg will not work on a MWBC's common neutral.
 
don_resqcapt19 said:
There is no requirement that a multiwire branch circuit be on a 2 pole breaker. Single pole breakers with handle ties are fine and very common on multiwire branch circuits.
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Handle ties are fine per 210.4(B). UNLESS there are both 120V and 240V loads on the MWBC (unusual, I know), then it must be a 2-pole common trip breaker per 210.4(C) Exception #2.
 
BarryO said:
Yes but those are covered by Exception #1 (supplies only one utilization equipment). I remember back in the day there were some ranges with convenience 120V receptacles on them; do they still exist?
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No but there is the situation that's possible where you utilize the range circuit tap rule with a nuetral requiring oven and a non nuetral requiring straight 240 cooktop.
 
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