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Hi All,

I am commercial electrician. However, I have went back into the field after several of being out of construction all together.

I need a little help, is it still permitted to share the neutrals on a 3 phase service or is the code now to pull a separate neutral for each circuit?
 

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Small Potatoes
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5,460 Posts
Hi All,

I am commercial electrician. However, I have went back into the field after several of being out of construction all together.

I need a little help, is it still permitted to share the neutrals on a 3 phase service or is the code now to pull a separate neutral for each circuit?
200.4 Neutral Conductors. Neutral conductors shall not be used for more than one branch circuit, for more than one multiwire branch circuit, or for more than one set of ungrounded feeder conductors unless specifically permitted elsewhere in this Code. (2011 NEC)
 

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Salty Member
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31,081 Posts
Yes you can still do that with some additional rules.

The NEC calls it a MultiWire Branch Circuit. (On the forum we call it a MWBC)

1) You have to use a handle tie across the single pole breakers or you can use a multi-pole breaker.

2) If the MWBC circuit enters the panel by a raceway with other circuits you have to group the MWBC so you can tell which neutral is being used with which hots.

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.

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.

(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.



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

(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.
240.15 Ungrounded Conductors.

(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 Circuit. 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-toneutral
loads.
 

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I'm not clear on the question... Are you asking about tapping off the service or are we talking about breakers? If we're talking about the service it depends are we talking about a main distribution panel... Cause it has extra lugs for that purpose but as far as three phase if you're sharing a neutral the wires need to be be on a two, three, ect.. Breaker
 

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Salty Member
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31,081 Posts
I'm not clear on the question... Are you asking about tapping off the service or are we talking about breakers? If we're talking about the service it depends are we talking about a main distribution panel... Cause it has extra lugs for that purpose but as far as three phase if you're sharing a neutral the wires need to be be on a two, three, ect.. Breaker
What the heck are you talking about?:blink:


And you don't have to use a two or three pole breaker, you can use single poles with handle ties.

I posted the rules ...
 

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Yes you can but the chances of the supply house having them in stock depending on what kind of breakers you're talking about is slim so you have to outweigh the thing and as far as I know you can't breaker tie 277/480... I could be wrong and if I am could someone direct me to that... Cause I've never seen and was told on a job by an inspector that it's not aloud... But then again he thought the 120 panel was 277.
 

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I'm not clear on the question... Are you asking about tapping off the service or are we talking about breakers? If we're talking about the service it depends are we talking about a main distribution panel... Cause it has extra lugs for that purpose but as far as three phase if you're sharing a neutral the wires need to be be on a two, three, ect.. Breaker
Yes you can but the chances of the supply house having them in stock depending on what kind of breakers you're talking about is slim so you have to outweigh the thing and as far as I know you can't breaker tie 277/480... I could be wrong and if I am could someone direct me to that... Cause I've never seen and was told on a job by an inspector that it's not aloud... But then again he thought the 120 panel was 277.
nec article 210.4 b looked it up in the book today while waiting for an inspector.
As MTW would say:

:rolleyes::rolleyes::rolleyes::rolleyes::rolleyes:
 
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