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PastorKramer 11-19-2012 04:33 PM

Common Neutral in Jct Box???
Several years ago I added a 2nd story w/ separate subpanel (my own home). Used all 3/4" flex metal conduit in 2nd story (I was a contractor & had several 100' given to me by one of my suppliers closing up shop & I had 1000s of feet of THHN, etc. on hand). Used a gutted 200A panel in attic as a large jct box (is about 8 - 10' from subpanel in 2nd floor living space). ALL boxes (main, sub & jct) are bonded/grounded.

Sub has isolated neutral bus bar. Ran same sized THHN neutral (main to sub) from sub to attic jct box and attached it to an isolated neutral bus bar in jct box. ALL circuit neutrals terminate on that jct box isolated neutral buss bar. I was sure that the inspector (15+ years ago said that was fine/approved)

Bottomline, never had "final" on structure... (health/financial issues) and now under a "new administration", I'm told that I have to run all the circuit neutrals back to the sub panel! I can't find a copy of my old code book now... and all the previous inspectors that I regularly used while in business are long since gone... The "new" inspector initially raised concerns that my neutral from the sub to the jct box might not be large enough... but then later called back/left msg saying that a common neutral was not allowed by code.

I'm puzzled, my electrical work (res & comm) was always considered "code plus" by previous inspectors -- never had any significant problems -- AND always asked them before doing the work IF I had a concern (unusual situation). Did I totally miss something in the code? As I said, it's the same size neutral from the main to the sub to the jct box... so don't understand the inspector initially telling me that I need a heavier feed to the jct box then what feeds the sub????? ... and now he says a common neutral buss bar is NOT ALLOWED. Period. ????? AGAIN, has the code changed (I think it was 1993) OR was it never allowed and the first inspectors (and myself) were in error? Thanks!

jbfan 11-19-2012 04:41 PM

All grounded conductors need to be inside the same conduit or cable as the hot wire.
You do have a violation.

Techy 11-19-2012 06:17 PM

This is actually a recent change, neutrals are no longer allowed to be used for more than one branch circuit, multiwire branch circuit, or feeder. NEC 2011 200.4

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 un-grounded feeder conductors unless specifically permitted
elsewhere in this Code.

Other permissions, do not apply to your case.

215.4 (A)

215.4 Feeders with Common Neutral Conductor.

(A) Feeders with Common Neutral. Up to three sets of
3-wire feeders or two sets of 4-wire or 5-wire feeders shall
be permitted to utilize a common neutral.
(B) In Metal Raceway or Enclosure. Where installed in a
metal raceway or other metal enclosure, all conductors of
all feeders using a common neutral conductor shall be en-
closed within the same raceway or other enclosure as re-
quired in 300.20.


225.7 (B)

225.7 Lighting Equipment Installed Outdoors.

(A) General. For the supply of lighting equipment in-
stalled outdoors, the branch circuits shall comply with Ar-
ticle 210 and 225.7(B) through (D).
(B) Common Neutral. The ampacity of the neutral conduc-
tor shall not be less than the maximum net calculated load
current between the neutral conductor and all unground
conductors connected to any one phase of the circuit.

PastorKramer 11-19-2012 10:40 PM

fyi, the inspector was fine with the ground buss bar in the attic jct box -- no "ground" problem / not the issue of this question

He said even tho the neutral bar is isolated (not connected to the metal panel jct box), I now need to run / extend all the nuetral conductors (now connected to the buss bar) thru the jct box and down to the subpanel -- essentially I'll have to add additional conduit or raceway and wire nut about 10' on to every neutral to be able to reach the subpanel.

Techy 11-20-2012 06:47 AM

hots and neutrals must be together in the same raceway 300.3 (b)

300.3 Conductors.

(B) Conductors of the Same Circuit. All conductors of
the same circuit and, where used, the grounded conductor
and all equipment grounding conductors and bonding con-
ductors shall be contained within the same raceway, auxil-
iary gutter, cable tray, cablebus assembly, trench, cable, or
cord, unless otherwise permitted in accordance with
300.3(B)(1) through (B)(4).

(1) Paralleled Installations. Conductors shall be permit-
ted to be run in parallel in accordance with the provisions
of 310.10(H). The requirement to run all circuit conductors
within the same raceway, auxiliary gutter, cable tray, trench,
cable, or cord shall apply separately to each portion of the
paralleled installation, and the equipment grounding conduc-
tors shall comply with the provisions of 250.122. Parallel runs
in cable tray shall comply with the provisions of 392.20(C).
Exception: Conductors installed in nonmetallic raceways
run underground shall be permitted to be arranged as iso-
lated phase installations. The raceways shall be installed in
close proximity, and the conductors shall comply with the
provisions of 300.20(B).
(2) Grounding and Bonding Conductors. Equipment
grounding conductors shall be permitted to be installed
outside a raceway or cable assembly where in accor-
dance with the provisions of 250.130(C) for certain ex-
isting installations or in accordance with 250.134(B),
Exception No. 2, for dc circuits. Equipment bonding
conductors shall be permitted to be installed on the out-
side of raceways in accordance with 250.102(E).
(3) Nonferrous Wiring Methods. Conductors in wiring
methods with a nonmetallic or other nonmagnetic sheath,
where run in different raceways, auxiliary gutters, cable
trays, trenches, cables, or cords, shall comply with the pro-
visions of 300.20(B). Conductors in single-conductor Type
MI cable with a nonmagnetic sheath shall comply with the
provisions of 332.31. Conductors of single-conductor Type
MC cable with a nonmagnetic sheath shall comply with the
provisions of 330.31, 330.116, and 300.20(B).

(4) Enclosures. Where an auxiliary gutter runs between a
column-width panelboard and a pull box, and the pull box
includes neutral terminations, the neutral conductors of cir
cuits supplied from the panelboard shall be permitted to
originate in the pull box.

AllanJ 11-20-2012 07:10 AM

As a general rule, when the hot conductor passes through a junction box on the way to the breaker panel, or different sub branches come together to become one branch circuit whose hot conductor continues on to its panel breaker, the neutral for that branch circuit must be separate, accompanying the hot conductor to the same panel and landing on the neutral bus in that panel.

Exceptions permitting one fatter neutral to be shared by multiple branch circuits have already been mentioned above and for the most part these exceptions are not encountered often.

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