Multiwire Branch Ciruits

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Ondarc

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Just a quick question, any input is welcome and very much appreciated. When and how is it legal according to the 2017 NEC to use 12/3 NM-B cable for multiple receptacle or lighting circuits in a residential setting?
Thanks.
 
Ondarc said:
Just a quick question, any input is welcome and very much appreciated. When and how is it legal according to the 2017 NEC to use 12/3 NM-B cable for multiple receptacle or lighting circuits in a residential setting?
Thanks.
Click to expand...

Perfectly legit. However you would not want to. Ask yourself how are you going to AFCI the circuits? 2 pole AFCI are expensive. Some manufactures allow single pole to be used and they will need to be handle Tied.

I would not it just complicates things.
 
Sierrasparky said:
Perfectly legit. However you would not want to. Ask yourself how are you going to AFCI the circuits? 2 pole AFCI are expensive. Some manufactures allow single pole to be used and they will need to be handle Tied.

I would not it just complicates things.
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But can you not use 12/3 on tied single pole breakers?

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Anytime you wish to do so, as long as you meet some requirements.

210.4 Multiwire Branch Circuits.
(A) General. Branch circuits recognized by this article shall
be permitted as multiwire circuits. A multiwire circuit shall be
permitted to be considered as multiple circuits. All conductors
of a multiwire branch circuit shall originate from the same
panelboard or similar distribution equipment.
Informational Note No. 1: A 3-phase, 4-wire, wye-connected
power system used to supply power to nonlinear loads may
necessitate that the power system design allow for the possibility
of high harmonic currents on the neutral conductor.
Informational Note No. 2: See 300.13(B) for continuity of
grounded conductors on multiwire circuits.
(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.
 
Only where disconnecting means uses 2-pole breaker, or handle ties across single poles, 210.4(B)

Not allowed where devices can interrupt neutral continuity (without pigtails), 300.13(B)

Not allowed for stand-alone power systems (Off Grid Solar Arrays, Batteries, or Generators), 710.15(C)

See all restrictions by searching the 2017 NPFA-70 PDF for keyword "multiwire"
 
HappElectrician said:
But can you not use 12/3 on tied single pole breakers?

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Yes you can use 12/3 or 14/3 as long as the breakers have a handle tie and of course are not on the same phase. I did not state the obvious as we are all supposed to know that you cannot have both circuits on the same phase.

packersparky said:
Anytime you wish to do so, as long as you meet some requirements.

210.4 Multiwire Branch Circuits.
(A) General. Branch circuits recognized by this article shall
be permitted as multiwire circuits. A multiwire circuit shall be
permitted to be considered as multiple circuits. All conductors
of a multiwire branch circuit shall originate from the same
panelboard or similar distribution equipment.
Informational Note No. 1: A 3-phase, 4-wire, wye-connected
power system used to supply power to nonlinear loads may
necessitate that the power system design allow for the possibility
of high harmonic currents on the neutral conductor.
Informational Note No. 2: See 300.13(B) for continuity of
grounded conductors on multiwire circuits.
(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.
Click to expand...


Thanks

ramsy said:
Not allowed for stand-alone power systems (Off Grid Solar Arrays, Batteries, or Generators), 710.15(C)

See all restrictions by searching the 2017 NPFA-70 PDF for keyword "multiwire"
Click to expand...

I don't see where stand alone power system is relevant to this topic?
 
Sierrasparky said:
Yes you can use 12/3 or 14/3 as long as the breakers have a handle tie and of course are not on the same phase. I did not state the obvious as we are all supposed to know that you cannot have both circuits on the same phase.




Thanks



I don't see where stand alone power system is relevant to this topic?
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Maybe the residence in question is off-grid? :angel:
 
Sierrasparky said:
Yes you can use 12/3 or 14/3 as long as the breakers have a handle tie and of course are not on the same phase. I did not state the obvious as we are all supposed to know that you cannot have both circuits on the same phase.




Thanks



I don't see where stand alone power system is relevant to this topic?
Click to expand...
Thx. I'm new here, and learning. ;)

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A word of advice--- "Don't use a multiwire branch circuit in a residence"..... It can cause more problems than it's worth. Before the afci were required the multiwire branch circuit was fairly common but you don't see it done anymore
 
Ondarc said:
Just a quick question, any input is welcome and very much appreciated. When and how is it legal according to the 2017 NEC to use 12/3 NM-B cable for multiple receptacle or lighting circuits in a residential setting?
Thanks.
Click to expand...

You might also want to consider using either 12/2/2 or 14/2/2 NM for this type of installation. You have two separate circuits but only one cable/homerun.
 
Ondarc said:
Just a quick question, any input is welcome and very much appreciated. When and how is it legal according to the 2017 NEC to use 12/3 NM-B cable for multiple receptacle or lighting circuits in a residential setting?
Thanks.
Click to expand...

You might also want to consider using either 12/2/2 or 14/2/2 NM for this type of installation. You have two separate circuits but only one cable/homerun.
 
1793 said:
That is another benefit. I use these cables quite a bit on remodels and room additions.
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Do you see that big of a labor or material savings? That stuff is about 45% more in cost.
I see the use for heat fans and such that have multiple switch legs.
 
GoldDigger said:
Maybe the residence in question is off-grid? :angel:
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Residences in Florida and several US territories went off grid, after recent hurricanes.

710.15(C) prohibits MWBC's for "Stand-Alone Systems" preferred in off-grid areas.

WARNING:
SINGLE 120-VOLT SUPPLY. DO NOT CONNECT MULTI‐
WIRE BRANCH CIRCUITS!
The warning sign(s) or label(s) shall comply with 110.21(B).
​
 
ramsy said:
Residences in Florida and several US territories went off grid, after recent hurricanes.

710.15(C) prohibits MWBC's for "Stand-Alone Systems" preferred in off-grid areas.

WARNING:
SINGLE 120-VOLT SUPPLY. DO NOT CONNECT MULTI‐
WIRE BRANCH CIRCUITS!
The warning sign(s) or label(s) shall comply with 110.21(B).
​
Click to expand...

I don't think the OP being in New York is concerned about off grid applications. I could be mistaken.
 
flatlander said:
I don't think the OP being in New York is concerned about off grid applications. I could be mistaken.
Click to expand...

Whats A-Matter You, Why You Looka So Sad, It's A-Not So Bad, just because this topic is relevant to Residential "Stand-Alone Systems" that are installed everywhere, not just Off-Grid areas.
 
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With the op being from NYC your only allowed to uses NM in residential buildings 3 stories or less

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