Multi-wire branch circuit

[Gregdoo]

Replaced the 1960s main panel (old Fed. Pacific) and have MWBC in conduit on most circuits. Have breaker handle ties on the shared circuits.

I'm upgrading some circuits and adding to some. Two questions for those of you that have worked with these shared-common circuits.

1) Can I have a 20 amp and a 15 amp circuit sharing the same 12 gauge neutral? (The 15 amp circuit has a 14 gauge hot) This is how it was originally wired, but I'm not sure if it is still kosher.


2) Similarly, can I have a GFCI -protected circuit and a non-GFCI circuit sharing the same neutral (with breaker ties)?

Thanks in advance for the info!

 

[ishiboo]

Replaced the 1960s main panel (old Fed. Pacific) and have MWBC in conduit on most circuits. Have breaker handle ties on the shared circuits.

I'm upgrading some circuits and adding to some. Two questions for those of you that have worked with these shared-common circuits.

1) Can I have a 20 amp and a 15 amp circuit sharing the same 12 gauge neutral? (The 15 amp circuit has a 14 gauge hot) This is how it was originally wired, but I'm not sure if it is still kosher.


2) Similarly, can I have a GFCI -protected circuit and a non-GFCI circuit sharing the same neutral (with breaker ties)?

Thanks in advance for the info!

1) Safety-wise yes, the neutral would have to be sufficient to carry the highest current... 12ga is fine for 20 amps. You could not have a 14ga neutral with one 20a leg. Not sure about code, but no safety issues in doing so.

2) Yes and no. You can have point GFCIs at outlets, but I dot believe you can have a GFCI feeding downstream receptacles.

 

[Charles (in GA)]

One GFCI breaker will not work, it will trip. The neutral passes thru it, and it will see the neutral current being different from the hot due to the other hot and trip. You will have to use individual GFCI receptacles on each outlet position you need GFCI protection on.

Charles

 

[Norcal]

A single pole GFCI circuit breaker will not work on a multi-wire circuit, well it will until a load is placed on the other leg of the multi-wire circuit & it senses a imbalance in the shared neutral. There is no issue w/ GFCI receptacles downstream of a multi-wire as long as one does not share a neutral w/ another circuit.

 

[Charles (in GA)]

This is all the NEC 2011 has to say about Multi-Wire Branch Circuits, that I have found.

If any of the other code gurus find anything I have missed, let me know, and I'll edit this post to include the information.

Also note, the reference to "identified handle tie" means that you must use the handle tie designed by the manufacturer of the circuit breaker for the purpose of connecting the handles to provide a common trip of both circuit breakers...... YOU CANNOT USE A NAIL DROPPED THRU THE HOLES IN THE HANDLES.

Definitions

ARTICLE 100 - Definitions

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.

General reference to MWBC

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: 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.

(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.

Informational Note: See 240.15(B) for information on the
use of single-pole circuit breakers as the disconnecting
means.

(C) Line-to-Neutral Loads. Multiwire branch circuits
shall supply only line-to-neutral loads.

Exception No. 1: A multiwire branch circuit that supplies
only one utilization equipment.
Exception No. 2: Where all ungrounded conductors of the
multiwire branch circuit are opened simultaneously by the
branch-circuit overcurrent device.

Informational Note: See 300.13(B) for continuity of
grounded conductor on multiwire circuits.

(D) Grouping. The ungrounded and grounded circuit conductors
of each multiwire branch circuit shall be grouped
by cable ties or similar means in at least one location within
the panelboard or other point of origination.

Exception: The requirement for grouping shall not apply if
the circuit enters from a cable or raceway unique to the
circuit that makes the grouping obvious.

With reference to circuit protection devices

240.15 Ungrounded Conductors.
(A) Overcurrent Device Required. A fuse or an overcurrent
trip unit of a circuit breaker shall be connected in
series with each ungrounded conductor. A combination of a
current transformer and overcurrent relay shall be considered
equivalent to an overcurrent trip unit.

Informational Note: For motor circuits, see Parts III, IV, V,
and XI of Article 430.

(B) Circuit Breaker as Overcurrent Device. Circuit breakers
shall open all ungrounded conductors of the circuit both
manually and automatically unless otherwise permitted in
240.15(B)(1), (B)(2), (B)(3), and (B)(4).

(1) Multiwire Branch Circuits. Individual single-pole circuit
breakers, with identified handle ties, shall be permitted
as the protection for each ungrounded conductor of multiwire
branch circuits that serve only single-phase line-to neutral
loads.

... snip ....

With reference to wiring practices, both mechanical and electrical specific to MWBC

300.13 Mechanical and Electrical Continuity — Conductors.
(A) General. Conductors in raceways shall be continuous
between outlets, boxes, devices, and so forth. There shall be
no splice or tap within a raceway unless permitted by 300.15;
368.56(A); 376.56; 378.56; 384.56; 386.56; 388.56; or 390.7.
(B) Device Removal. In multiwire branch circuits, the
continuity of a grounded conductor shall not depend on
device connections such as lampholders, receptacles, and
so forth, where the removal of such devices would interrupt
the continuity.

 

[ishiboo]

300.13B interpreted means that you must pigtail both the ground and neutral instead of connecting them directly to the installed receptacles then, correct?

 

[Adrien]

300.13B interpreted means that you must pigtail both the ground and neutral instead of connecting them directly to the installed receptacles then, correct?

Correct.

Adrien

 

[Gregdoo]

210.4 D - Grouping.....not sure I understand what is being asked for here, can someone please explain?

Thanks for the other info. It sounds like I'm allowed to share my 12ga. neutral with both the 15 amp (14 ga.) and 20 amp (12 ga.) circuits.

Also sounds like my hope to use a 20 amp GFCI breaker in conjunction with a 15 amp regular breaker with shared neutral will not work and I would need to either run a separate neutral for that circuit or use GFI receptacles individually at those places needing protection.

Thanks for sharing your expertise and extracting the pertinent codes.

 

[ishiboo]

210.4 D - Grouping.....not sure I understand what is being asked for here, can someone please explain?

Thanks for the other info. It sounds like I'm allowed to share my 12ga. neutral with both the 15 amp (14 ga.) and 20 amp (12 ga.) circuits.

Also sounds like my hope to use a 20 amp GFCI breaker in conjunction with a 15 amp regular breaker with shared neutral will not work and I would need to either run a separate neutral for that circuit or use GFI receptacles individually at those places needing protection.

Thanks for sharing your expertise and extracting the pertinent codes.

It simply means that all wires of the circuit (the two hots, neutral and ground) need to be wire tied at some point in the panel... probably near where they enter. It's so you can clearly identify that all 4 wires are part of the same MWBC circuit.

In newer installs than yours, I think this would be unnecessary if you ran x/3 NM into the panel with the sheath visible, though it wouldn't hurt to wire tie.

 

[kingspec]

Hello,
I'm new to this forum and I noticed I'm in a thread that has had no activity for a couple of years. Guess I'll see if anyone sees this before starting a new thread because my question is related to this threads' subject.

I've wired several circuits in my basement using 12-3w/g in the following manner, and would like to know if it will meet code:

For example, I ran a 20 amp circuit to a bedroom, and added an additional 12 gauge neutral (white) wire, wire-tied to the Romex every foot. At the first box in this bedroom, I wire-nutted the red wire, the additional white, and ground to a new 12-2w/g going to the next bedroom. Each room is on a separate 20a breaker, next to each other in the box, so as to be on different phases.

Anyone see a problem, either from any safety standpoint--or inspection issue?

Additionally, I also wire-tied an additional 12ga conductor every foot to a 12/2w/g romex and used it in a 3-way lighting circuit. Kosher? Or not?

Thanks for any responses.

Kingspec

 

[Charles (in GA)]

Others will chime in but there is too much wrong with this. You cannot run the individual wire along with but outside the jacketed wire.

Charles

 

[frankush]

I'm not in an area where romex is allowed, but I totally agree with Charles on this one. Romex is approved as a multiwire "assembly". (for lack of a better term) Individual circuit wires are not meant to be pulled through walls. I doubt you could pass an inspection using that wiring method.

 

[wyliesdiesels]

This wont pass inspection because individual wires need to be in conduit!

 

[DesertSparky57]

What you've done is free air wiring. Your method of adding more conductors is very very far from kosher.

When you were crawling along the wire with zip ties, you should have been pulling a new NM run instead. I'm not trying to belittle you, but your method is wrong on many levels.