2 SABC's as a multiwire circuit

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It just occurred to me, even though I've done dozens of these..
If the two kitchen SABC's are set up as a MWBC, obviously the home run can be done with a single 12/3, but after that, the circuit splits into two separate runs of 12/2.
What about the NEC provision that all conductors belonging to the same circuit must be within the same conduit or cable assembly? Doesn't splitting of the single multiwire circuit into two cables or conduits at the end the home run violate that rule??
 
IMHO no, because all of the conductors of each single SABC derived from an MWBC home run are present wherever that SABC goes.

Wait..
Do you mean that the 12/3 goes through all the receptacle boxes? if that's the case, then you're right.

However, I've seen it (and installed it a few times myself, at my boss's behest) where at the end of the home run the 12/3 splits into two 12/2's, running to two different sets of countertop receptacles.
Sure, those two runs have the common neutral, but each run of 12/2 is missing the other one's hot conductor within the cable assembly.
Is that a violation?
We passed the inspection every time, but that doesn't mean much..
Or, is a multiwire branch circuit is treated as TWO separate circuits??
I am soooooo confused :happysad:
Especially considering that I've done this many, many times..
 

kwired

Electron manager
Location
NE Nebraska
Once you split, you no longer have a multiwire circuit. Even if you run the second ungrounded conductor to an outlet but cap it off, you are still only using it as a two wire circuit at that point.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Wait..
Do you mean that the 12/3 goes through all the receptacle boxes? if that's the case, then you're right.

However, I've seen it (and installed it a few times myself, at my boss's behest) where at the end of the home run the 12/3 splits into two 12/2's, running to two different sets of countertop receptacles.
Sure, those two runs have the common neutral, but each run of 12/2 is missing the other one's hot conductor within the cable assembly.
Is that a violation?
We passed the inspection every time, but that doesn't mean much..
Or, is a multiwire branch circuit is treated as TWO separate circuits??
I am soooooo confused :happysad:
Especially considering that I've done this many, many times..

You are working to hard at this. Look at the SE to your home. It is a multi wire circuit. Two hot and a neutral. Do you worry about splitting the circuits off at each breaker?
The MWBC as you describe used to be treated as TWO separate circuits but now it must have handle ties at the breakers so if one breaker is turned off, both go off. You may still split the circuit at a junction box as you always have done.
 

kwired

Electron manager
Location
NE Nebraska
Ultimately all the 120 volt loads connected to this circuit only use two of the three wires of the circuit, you don't have to extend the third wire to where it is not being used. The rule that all circuit conductors be in same raceway or cable means all conductors carrying same current to same load need to be in same raceway or cable. This is so that magnetic effects of the current in those conductors will have a canceling effect on one another, which 1, reduces electromagnetic fields in the area, and 2, has an overall lowering of impedance of those conductors. The effects may not be so obvious with most general use types of circuits, but they are still there.
 
You are working to hard at this. Look at the SE to your home. It is a multi wire circuit. Two hot and a neutral. Do you worry about splitting the circuits off at each breaker?
The MWBC as you describe used to be treated as TWO separate circuits but now it must have handle ties at the breakers so if one breaker is turned off, both go off. You may still split the circuit at a junction box as you always have done.

Thanks, guys. I'm relieved, really.

Yep, I learned the need for the handle tie pretty quick.
That was, for once, a good recent addition to the NEC.
A time or two, while working in an old panel, I got zapped by a neutral that I've just disconnected from the busbar, because it carried a current from the other half of the MWBC. No handle tie was to be found on those breakers.

Then again, even for the circuits that weren't meant to be MWBC's, I've come across 'stolen neutrals', used by a completely different circuit. One can only hope that the hot conductors for those two circuits are on different phases...
My recent crazy "old work" find was the jacket of the AC cable used for the neutral.. Lots of crazy folks out there, never know what surprises you'll find. That's why I love our trade.
That, or maybe because I'm new to it :)
 
Ultimately all the 120 volt loads connected to this circuit only use two of the three wires of the circuit, you don't have to extend the third wire to where it is not being used. The rule that all circuit conductors be in same raceway or cable means all conductors carrying same current to same load need to be in same raceway or cable. This is so that magnetic effects of the current in those conductors will have a canceling effect on one another, which 1, reduces electromagnetic fields in the area, and 2, has an overall lowering of impedance of those conductors. The effects may not be so obvious with most general use types of circuits, but they are still there.

That's the explanation I can understand, thanks much, kwired
 

Ponchik

Senior Member
Location
CA
Occupation
Electronologist
We're still on 2011, so unless I'm seriously mistaken 210.12 does not include kitchens in the 2011 cycle.

For the 2011 NEC, One of the MWBC must supply the dining room receptacles, hence one of the circuits is required to have AFCI protection.
 
Then you will end up with three SABC and one of those has to be AFCI protected.

So far, the absolute majority of the times, at least on the jobs that I've been on, we've done two SABC's as a multiwire circuit on a regular two-pole breaker using 12/3, and a separate dining room circuit using 12/2 protected by an AFCI.

My original question had to do with whether it is OK to split an MWBC into two 12/2's at the end of the 12/3 homerun, and I got my answer, but like you said, this question will become moot after our locale moves to the 2014.

Unless they adopt 2017 when that comes out, and skip the 2014 altogether. Same result though -- no SABC multiwire circuits.
 

kwired

Electron manager
Location
NE Nebraska
So far, the absolute majority of the times, at least on the jobs that I've been on, we've done two SABC's as a multiwire circuit on a regular two-pole breaker using 12/3, and a separate dining room circuit using 12/2 protected by an AFCI.

My original question had to do with whether it is OK to split an MWBC into two 12/2's at the end of the 12/3 homerun, and I got my answer, but like you said, this question will become moot after our locale moves to the 2014.

Unless they adopt 2017 when that comes out, and skip the 2014 altogether. Same result though -- no SABC multiwire circuits.

Double pole AFCI would allow this, but may not be cost effective method, and may not be available from all manufacturers at this point anyway.
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
So far, the absolute majority of the times, at least on the jobs that I've been on, we've done two SABC's as a multiwire circuit on a regular two-pole breaker using 12/3, and a separate dining room circuit using 12/2 protected by an AFCI.

My original question had to do with whether it is OK to split an MWBC into two 12/2's at the end of the 12/3 homerun, and I got my answer, but like you said, this question will become moot after our locale moves to the 2014.

Unless they adopt 2017 when that comes out, and skip the 2014 altogether. Same result though -- no SABC multiwire circuits.

Question, why do you run a separate circuit for the dinning room? Code lets you tap off the kitchen counter circuit.
 
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