current carrying neutral

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hhsting

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I have an on going argument with local inspector regarding neutral is current carrying. I am feeding 11 circuits, 120V, single phase: 1 phase 1 neutral from 120/208V three phase 4 wire panelboard in one conduit with one common EGC. I am counting 11 current carrying conductors all phase.

NEC 2014 Article 310.15(B)(5)(a): neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted when applying the provisions of 310.15(B)(3)(a).

In my case I have neutral conductor that carries unbalanced current from other conductors. However, inspector seems to disagree says current carrying conductors I have are 22 neutral is counted as current carrying but did not say why even though asked multiple times.

I have read from previous post charts that indicate inspector maybe correct but 310.15(B)(5)(a) specifically says neutral is not counted when carrying unbalanced current from other circuits.

Is inspector correct? If so then under what argument is he correct?
 
Clarify for me please. 11 phase conductors and how many neutral conductors ?
 
you would have 22 current carrying conductors. You are not sharing any neutrals/
all the current flowing thru one of your phase conductors flows back thru its neutral.
(requiring a .45 multiplier).
 
First of all, the only time different hot (ungrounded) conductors can share a neutral is when the neutral serves a single MWBC with a disconnect device (like breaker) which opens all hot conductors at once. (Either a common trip breaker or independent poles with a handle tie(s).
Your 11 circuits, if fed from a full four wire three phase panel (three hots and a neutral) can be combined, at best, into three three phase MWBCs ("full boats") and two circuits left over. The two remaining could be an MWBC with the neutral counted as current carrying, and so you would have a total of 12 conductors for the three full MWBCs and three conductors for the single partial MWBC. Of the four neutrals involved, only one ( from the partial MWBC) would be counted as current carrying under NEC rules.
If you are trying to run 11 hots and only one shared neutral, that is an NEC violation independent of derating (adjustment and correction) issues.

PS: What Augie said.

If you have a two wire circuit, the issue of imbalance in a multiwire circuit does not even apply.
 
GoldDigger said:
First of all, the only time different hot (ungrounded) conductors can share a neutral is when the neutral serves a single MWBC with a disconnect device (like breaker) which opens all hot conductors at once. (Either a common trip breaker or independent poles with a handle tie(s).
Your 11 circuits, if fed from a full four wire three phase panel (three hots and a neutral) can be combined, at best, into three three phase MWBCs ("full boats") and two circuits left over. The two remaining could be an MWBC with the neutral counted as current carrying, and so you would have a total of 12 conductors for the three full MWBCs and three conductors for the single partial MWBC. Of the four neutrals involved, only one ( from the partial MWBC) would be counted as current carrying under NEC rules.
If you are trying to run 11 hots and only one shared neutral, that is an NEC violation independent of derating (adjustment and correction) issues.

PS: What Augie said.

If you have a two wire circuit, the issue of imbalance in a multiwire circuit does not even apply.
Click to expand...
How does the last 2 phase and neutral partial MWBC is counted as 3 current carraying? Neutral is unbalanced from lets say Phase A and Phase B currents.

And on full MWBC neutral if all loads same would be balanced so counted as current carrying?
 
hhsting said:
How does the last 2 phase and neutral partial MWBC is counted as 3 current carraying? Neutral is unbalanced from lets say Phase A and Phase B currents.

And on full MWBC neutral if all loads same would be balanced so counted as current carrying?
Click to expand...

Basically, for the neutral to not count as a CCC, it has to be a "full" MWBC. In other words, on a three phase wye system, you need all three hots. You dont get a discount for a MWBC with only two hots.
 
The inspector is right. A neutral must be shared with conductors of all hot legs of multiwire system to qualify under 310.15(5)(a).* (It must also pass muster under (c).) A circuit consisting of two conductors has two current carrying conductors.

*exception: high leg delta doesn't need the high leg
 
This may help:

Neutral Conductors:
Here's some examples of when to count and not count the neutral as a current
carrying conductor or CCC:

3Ø- 208Y/120 or 480Y/277 volt system-different circuit types:
A) 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
B) 3 wire circuit w/ 2 ungrounded, 1 neutral = 3 CCC's
C) 4 wire circuit w/ 3 ungrounded, 1 neutral = 3 CCC's*

Notes:
A) A normal 2 wire circuit has equal current flowing in each of the circuit
conductors so they both count as CCC's.
B) In this circuit the neutral current will be nearly equal to the current in the
ungrounded conductors so the neutral counts as a CCC
C) In this circuit the neutral will only carry the imbalance of the current between
the three ungrounded conductors so it is not counted as a CCC, with an exception,
*if the current is more than 50% nonlinear (see below for NEC article 100
definition) then the neutral would count as a CCC.


1Ø- 120/240 volt system-different circuit types:
D) 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
E) 3 wire circuit w/ 2 ungrounded, 1 neutral = 2 CCC's


Notes:
D) A normal 2 wire circuit has equal current flowing in each of the circuit
conductors so they both count as CCC's.
E) In this circuit the neutral will only carry the imbalance between the two
ungrounded conductors so the neutral is not counted as a CCC.
Nonlinear Load. A load where the wave shape of the steady-state current does
not follow the wave shape of the applied voltage.
Informational Note: Electronic equipment, electronic/electric-discharge lighting,
adjustable-speed drive systems, and similar equipment may be nonlinear loads.
Click to expand...
 
hhsting said:
How does the last 2 phase and neutral partial MWBC is counted as 3 current carraying? Neutral is unbalanced from lets say Phase A and Phase B currents.

And on full MWBC neutral if all loads same would be balanced so counted as current carrying?
Click to expand...
1. Because it is not a full MWBC the only-if-unbalanced rule does not apply. In fact since L1-N and L2-N are 120 degrees out of phase (call it 0 degrees and 120 degrees.), if they are balanced the neutral current will be exactly the same magnitude as the L1 and L2 current, but at 240 degrees.
2. For a full three phase MWBC the vector sum of the line currents is zero, so no current on the neutral. To get neutral current you have to reduce one line current, and the resistive heating stays more or less the same.
 
hhsting said:
NEC 2014 Article 310.15(B)(5)(a): neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted when applying the provisions of 310.15(B)(3)(a).

In my case I have neutral conductor that carries unbalanced current from other conductor{s}.
Click to expand...

In a two wire circuit the neutral carries the unbalanced current from another conductor (singular).
 
What everyone has told you is true.

But, let me put his out there for you guys,
He pulls all "full boats" lands the last one, not needed, on a duplex off some place (side of panel) now he has reduced neut. like the rest of the mwbc?
 
hhsting said:
How does the last 2 phase and neutral partial MWBC is counted as 3 current carraying? Neutral is unbalanced from lets say Phase A and Phase B currents.
Click to expand...
Pick some random values for A and B and then use the following formula (only use A and B) to see the current on the neutral.
(A^2 + B^2 + C ^2)-(A*B+B*C+A*C)

hhsting said:
And on full MWBC neutral if all loads same would be balanced so counted as current carrying?
Click to expand...
Now use the formula again with all three phase conductors.

If there is a local VoTech that might have an electrical program it might be worth looking into.

Roger
 
sameguy said:
What everyone has told you is true.

But, let me put his out there for you guys,
He pulls all "full boats" lands the last one, not needed, on a duplex off some place (side of panel) now he has reduced neut. like the rest of the mwbc?
Click to expand...


What do you mean by reduced neutral?
 
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