NEC 310.15 E neutral conductor

roger said:
Read post #11 and perform the calculation I gave you in post #3. This should not be above your capabilities
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What value amperes do i assume for phases A, B and C to attempt to solve the equation in post 11?

Do i arbitrarily assign a random load vale or are the loads supposed to be ballanced?
 
Jpflex said:
memorizng all the varient systems and when to count neutral is difficult among all the other codes and exemptiins
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Those pictures you posted is what i was thinking but the more i read NEC the more confused i get. I absolutely hate how they word things
 
I acant exactly picture what NEC is saying in 3)

most 3 phase loads such as motors do not use the neutral.

Therefore, is 310.15 E 3 talking about each line 1 line to load and return to the conmon neutral? And if so under this condition with nonlinear loads we count the neutral?

Also what avout a delta with a derived neutral?
 
roger said:
Using the formular below figure it with 10 amps on three phase conductors and then with just two.

Nuetral = √(a² + b² + c² - ab - bc - ac)
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The square root of 0 is 0 answer
 
So simpler way to think about whether to count a neutral is to determine if this wire has the same amount of current as line or phase wires, although we may call it a neutral regardless?
 
Jpflex said:
So simpler way to think about whether to count a neutral is to determine if this wire has the same amount of current as line or phase wires, although we may call it a neutral regardless?
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The only times you don't count the neutral are:

1P3W circuits, e.g. 120/240V split-phase. This includes the center-tapped side of a high leg delta.
3P4W circuits, e.g. a wye or a high leg delta.

Cheers, Wayne
 
And 310.15 E (2) Must also be a MWBC. I wish NEC would cut the crap and just say this
 
wwhitney said:
The only times you don't count the neutral are:

1P3W circuits, e.g. 120/240V split-phase. This includes the center-tapped side of a high leg delta.
3P4W circuits, e.g. a wye or a high leg delta.

Cheers, Wayne
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This must depend on if a MWBC is used on this 1P3W because if its not MWBC you have individual lines and neutrals per load for this split phase 120/240 volt system.

I think you should count a 1P3W (SINGLE PHASE 3 WIRE) circuit unless its MWBC?
 
Jpflex said:
This must depend on if a MWBC is used on this 1P3W because if its not MWBC you have individual lines and neutrals per load for this split phase 120/240 volt system.
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If the circuit is 1P3W on a split-phase supply, the circuit consists of two (different) ungrounded conductors and a neutral. That's the 3W, 3 wires. So the neutral doesn't count.

You could install a 1P2W circuit on a split-phase supply, and as 1P2W is not on my list, you count the neutral.

One clarification on my previous post: in this context, even though people call a 3W 120/208V supply, consisting of 2 ungrounded and a neutral from a 3P4W wye system, "single phase", I did not mean to include that in "1P3W circuits". So if you want to call that 1P3W, then we need to change "1P3W circuits" to "1P3W circuits where the neutral is the center-tap of the two ungrounded conductors."

Cheers, Wayne
 
It's not really that complicated. Figure out what the circuit is and look at the chart in post #11. That will tell you when the neutral counts as a CCC.
 
Jpflex said:
The square root of 0 is 0 answer
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Ok let's use 10 for A
5 for B
8 for C

√(a² + b² + c² - ab - bc - ac)

A squared would be 10 x 10 =100
B squared would be 5 x 5 = 25
C squared would be 8 x 8 = 64
189

A x B 10 x 5 = 25
B x C 5 x 8 = 40
C x A 8 x 10 = 80
145

189
-145
_________
44
SQRT of 44 = 6.633

Now do the same calculation with just A and B
 
wwhitney said:
If the circuit is 1P3W on a split-phase supply, the circuit consists of two (different) ungrounded conductors and a neutral. That's the 3W, 3 wires. So the neutral doesn't count.

You could install a 1P2W circuit on a split-phase supply, and as 1P2W is not on my list, you count the neutral.

One clarification on my previous post: in this context, even though people call a 3W 120/208V supply, consisting of 2 ungrounded and a neutral from a 3P4W wye system, "single phase", I did not mean to include that in "1P3W circuits". So if you want to call that 1P3W, then we need to change "1P3W circuits" to "1P3W circuits where the neutral is the center-tap of the two ungrounded conductors."

Cheers, Wayne
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What i was thinking when you said 1P3W was a 1 phase or split phase with a tapped neutral mid way on secondary windings as a derived neutral.

This is the set up for most residential houses i see. So we dont count this neutral?
 
Jpflex said:
What i was thinking when you said 1P3W was a 1 phase or split phase with a tapped neutral mid way on secondary windings as a derived neutral.

This is the set up for most residential houses i see. So we dont count this neutral?
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For a 3-wire circuit, both ungroundeds and the neutral, correct, that's 2 CCCs. Any 2-wire circuit is always 2 CCCs.

Cheers, Wayne
 
Jpflex said:
Ok but is 310.15 E 1 referring specificslly to MWBC on single phase systems without simply saying this?

1) a neutral conductor that carries only the unballanced current from other conductirs of the same circuit shall NOT be requited to be counted as current carrying
...
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Not quite, not 'specifically'. That language could refer either to 2 hots and a neutral on a 120/240 circuit, or 3 hots and a neutral on a wye MWBC without enough non-linear load.
 
Jpflex said:
So if a neutral carries nearly as much current as the 2/3 phase line currents of a 3 phase system (assuming Y) then i would expect that you could not use a MWBC sharing the sane neutral because neutral current would be double here?
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No, not doubled. Suppose you have a fully-loaded wye MWBC with 20a on each line. You would have no neutral current. Reduce the load one one phase by 1a; the neutral would now carry that 1a.

Now, reduce the load on that same one phase by 5a; the neutral would now carry that 5a. Keep going until that phase has no load. The neutral current would now be 20a. It would never rise above that.

Jpflex said:
Each circuit would have to be supplied with its own neutral?
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You can, but you don't need to.
 
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