Unbalanced Current on Neutral

[MD12297]

Hello, When calculating the # of current carrying conductors for table 310.15 (B)(3)(a) I was looking at the exemption of 310.15 (B) (5) (a) Neutral conductor that carries only the unbalanced current from other conductors on the same circuits shall not be required to be counted....

So my question is, can someone give me an example of a balanced load vs unbalanced load? Something easy to understand in an every day example ?

If I ran 4 - single pole 20 amp circuits in a conduit and ran a separate neutral for each of them that's 8 conductors, but would the load types on the circuits matter regarding balanced vs unbalanced? say 2 circuits were for lighting and 2 were for receptacles. Sorry if this seems like a foolish question. Thanks for your help.

 

[infinity]

In 4-two wire circuits the load type wouldn't matter because you would have 8 CCC's. Take a look at this chart:

Neutral Conductors:
Here's some examples of when to count and not count the neutral as a current
carrying conductor or CCC:
3?- 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.
1?- 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.

 

[MD12297]

Thanks Rob! That was fast!

 

[GoldDigger]

Hello, When calculating the # of current carrying conductors for table 310.15 (B)(3)(a) I was looking at the exemption of 310.15 (B) (5) (a) Neutral conductor that carries only the unbalanced current from other conductors on the same circuits shall not be required to be counted....

So my question is, can someone give me an example of a balanced load vs unbalanced load? Something easy to understand in an every day example ?

If I ran 4 - single pole 20 amp circuits in a conduit and ran a separate neutral for each of them that's 8 conductors, but would the load types on the circuits matter regarding balanced vs unbalanced? say 2 circuits were for lighting and 2 were for receptacles. Sorry if this seems like a foolish question. Thanks for your help.

The irony (I won't call it a paradox) is that if you have two circuit pairs connected to opposite line polarity you could run the four circuits as two three wire MWBCs and not count the neutrals at all. Six conductors but counted as four conductors total. By putting in individual neutrals you add two more wires but now have to count all four neutrals. Eight counted CCCs.