neutral conductor table 310.15[B][3][a[

[Ted Moore]

I'm having trouble trying to make sense of article 310.15 [5], as it pertains to counting the neutral as a current carrying conductor when using a separate neutral with each current carrying conductor. I am under the impression that when not sharing neutral conductors with other current carrying conductors, shouldn't be counted when calculating adjustment factors of table 310.15 [3] [a], is that correct?

 

[Dennis Alwon]

If you are not sharing the neutral as in a 2 wire 120V circuit then you must count the neutral

 

[Dennis Alwon]

This may help



Here's some examples of when to count the neutral as a CCC:


208Y/120 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 one exception, *if the current is more than 50% nonlinear then the neutral would count as a CCC.


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 condcutors so the neutral is not counted as a CCC.

 

[Ted Moore]

neutral conductor counted as a current carrying conductor

neutral conductor counted as a current carrying conductor

I guess what makes this confusing is 310.15 [5] [a], which states that a neutral that carries only the unbalanced current from other conductors of the SAMECIRCUIT, [ makes no sense ], shall not be counted

 

[Smart $]

Only the neutral of a multiwire branch circuit with not more than 50% nonlinear load can be excepted from counting as a current carrying conductor.

That's the short of it.

 

[roger]

I guess what makes this confusing is 310.15 [5] [a], which states that a neutral that carries only the unbalanced current from other conductors of the SAMECIRCUIT, [ makes no sense ], shall not be counted

It makes perfect sense, see the simple illustrations below.

Roger

 

[kwired]

I guess what makes this confusing is 310.15 [5] [a], which states that a neutral that carries only the unbalanced current from other conductors of the SAMECIRCUIT, [ makes no sense ], shall not be counted

Multiwire circuits is where that applies. Multiwire circuits includes service and feeders that have a common neutral conductor that is shared between other conductors.

For a simple example lets stick to single phase 120/240 volts applications.

If you have 10 amps of current from line A to neutral and 10 amps of current from line B to same neutral conductor that ties to A, that neutral effectively sees no current, and doesn't produce additional heating in cables and raceways if not carrying any current.

Now lets put 10 amps on A and 5 amps on B, both to same neutral conductor. Now the unbalance is 5 amps and this unbalance will flow in the neutral. But for ampacity adjustments sake there is still similar amount of heating effects in the raceway or cable, 10 amps on A, 5 amps on B, and 5 amps on N.

Now if we put 10 amps on A, and incorrectly put 10 amps on A (that should have been on B)- sharing one neutral that neutral actually sees 20 amps of current, so heating effects in the raceway or cable are coming from 10, amps, 10 amps and 20 amps from same three conductors we had in the other examples.

 

[MrSmilez1959]

Just hook it up. If you get zapped on the neutral, then it should be considered a CCC, if not, then you're PROBABLY ok. But I'm still learning. Lol.


Sent from my iPhone using Tapatalk

 

[Dennis Alwon]

Just hook it up. If you get zapped on the neutral, then it should be considered a CCC, if not, then you're PROBABLY ok. But I'm still learning. Lol.


Sent from my iPhone using Tapatalk

Um,,, I don't think so

 

[roger]

But I'm still learning

And your post makes that obvious so stick around, this place has good teachers.

Roger

 

[MrSmilez1959]

It was a joke, that should've been obvious. Don't take life so serious. But I'm paying attention.


Sent from my iPhone using Tapatalk

 

[roger]

It was a joke, that should've been obvious.

It would probably a good idea to keep your day job.

See, you learned something by your second post.

Roger

 

[MD84]

It makes perfect sense, see the simple illustrations below.

Roger

That first diagram is enlightening and confusing all in one! Seeing the flow in both directions on the neutral allows one to understand that the current is cancelling out. Then thinking that there is no current flowing at all makes it confusing.

Writing this out helps again though. For the 120/240 example one could think of it as two 120V loads at 10A each for a total of 2400W. This is where I would imagine neutral current flowing in both directions. I could then think of it as one series 240V load at 10A for a total of 2400W. This is were I would imagine no current flowing on the neutral.

My next thought goes to an unbalanced load. I think this is were the neutral is important. In the latter 240V example were it is balanced, the neutral could be removed with no ill effect. The 240V would drop evenly across the loads, each load seeing 120V. If the load is not balanced then some current must flow on the neutral. With no neutral in unbalanced loads the voltage would drop disproportionately allowing a voltage exceeding that of the 120V load.

Does the neutral ensure each load is operating at 120V regardless of resistance?

 

[kwired]

Does the neutral ensure each load is operating at 120V regardless of resistance?

Yes, the presence of the neutral conductor is the "stabilizer" that ensures each load sees 120 volts. Should both loads be exactly same resistance the neutral is not necessary, but in order to work with no neutral connection and maintain 120 volts across the two loads, they need to be fixed at same resistance/impedance and never change.

Think of a dual voltage 120/240 volt motor. It basically has two 120 volt coils in it, when we connect it to 120 volts we put them in parallel and each sees 120 volts. When we connect it to 240 volts we put them in series and each has near identical impedance - so there is still 120 volts across each winding. You could connect a neutral to the mid point in that case but it shouldn't change much unless each coil is not the same impedance.

 

[squaredan]

Multiwire circuits is where that applies. Multiwire circuits includes service and feeders that have a common neutral conductor that is shared between other conductors.

For a simple example lets stick to single phase 120/240 volts applications.

If you have 10 amps of current from line A to neutral and 10 amps of current from line B to same neutral conductor that ties to A, that neutral effectively sees no current, and doesn't produce additional heating in cables and raceways if not carrying any current.

Now lets put 10 amps on A and 5 amps on B, both to same neutral conductor. Now the unbalance is 5 amps and this unbalance will flow in the neutral. But for ampacity adjustments sake there is still similar amount of heating effects in the raceway or cable, 10 amps on A, 5 amps on B, and 5 amps on N.

Now if we put 10 amps on A, and incorrectly put 10 amps on A (that should have been on B)- sharing one neutral that neutral actually sees 20 amps of current, so heating effects in the raceway or cable are coming from 10, amps, 10 amps and 20 amps from same three conductors we had in the other examples.

Well put, with all the hours of studying I have done and still do, never saw it that way..Makes total sense, thanks for sharing kwire..

 

[Ted Moore]

Ted Moore

Ted Moore

Thanks everyone, except for the first years helpers advise [ unnecessary]. The code book, as most of us know, tends to not make some things clear.

 

[kwired]

Thanks everyone, except for the first years helpers advise [ unnecessary]. The code book, as most of us know, tends to not make some things clear.

What we have here is rules in the code that have some electrical theory driving them. The NEC is not intended to teach electrical theory to those that don't know it, so if you don't understand the theory some of the code rules are harder to understand why we have them.

 

[mike1061]

Multiwire circuits is where that applies. Multiwire circuits includes service and feeders that have a common neutral conductor that is shared between other conductors.

For a simple example lets stick to single phase 120/240 volts applications.

If you have 10 amps of current from line A to neutral and 10 amps of current from line B to same neutral conductor that ties to A, that neutral effectively sees no current, and doesn't produce additional heating in cables and raceways if not carrying any current.

Now lets put 10 amps on A and 5 amps on B, both to same neutral conductor. Now the unbalance is 5 amps and this unbalance will flow in the neutral. But for ampacity adjustments sake there is still similar amount of heating effects in the raceway or cable, 10 amps on A, 5 amps on B, and 5 amps on N.

Now if we put 10 amps on A, and incorrectly put 10 amps on A (that should have been on B)- sharing one neutral that neutral actually sees 20 amps of current, so heating effects in the raceway or cable are coming from 10, amps, 10 amps and 20 amps from same three conductors we had in the other examples.

Thanks.
I knew the math inside and out, but I still (until today) thought you counted the neutral.
Thanks a lot.
Mike