Do I count the neutral in a 240, 3-wire circuit as a CCC?

[JoeNorm]

I know this wire will carry some current, but is it counted as a CCC for derating purposes?

Thanks

 

[ggunn]

Most of the time, no.

 

[infinity]

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.

 

[kwired]

Some potential terminology issues here?

Guessing you are talking about a 120/240 three wire circuit that uses two "hots" and a "neutral". In that case the neutral is not considered current carrying for the purpose of ampacity adjustments.

Otherwise there technically a 240 volt three wire circuit is all three phases and no neutral, in which all three are considered current carrying.

 

[infinity]

Otherwise there technically a 240 volt three wire circuit is all three phases and no neutral, in which all three are considered current carrying.

True, but would that have a neutral as mentioned in the title of this thread?

 

[ggunn]

Most of the time, no.

The reason being is that for every ampere carried by the neutral there is an ampere less carried by the L1 and L2 conductors. I'm no expert on motors, but I seem to remember that some motor circuits are an exception. Someone else will have to fill that in.

 

[roger]

True, but would that have a neutral as mentioned in the title of this thread?

Now that's hitting the nail on the head.
No it would not

Roger

 

[mhanson]

NEC 2017 - 310.15 (B)(a) states "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)"

So I'd say NO its not counted in a 3 wire circuit.

 

[Carultch]

I know this wire will carry some current, but is it counted as a CCC for derating purposes?

Thanks

Generally the answer is no, but here are two reasons why the answer would be yes:

1: If neutral is a mandatory part of the return path of the circuit, even for balanced loads, you count it.

Examples being:
A. single phase line-to-neutral circuits (this one is obvious)
B. the feeder derived from a pair of phases & neutral of a 3-phase system, that serves phase-to-neutral loads. Due to the fact that the phases are not equal and opposite, the neutral will still carry current even when these are balanced.

2. If the system has non-linear loads with significant harmonics, then you count it. Triplen harmonics on three phase in particular, will add up, instead of cancel. Or similarly, even harmonics on split-phase.

 

[LarryFine]

1A is incorrect. Any neutral current is current not being carried by a line conductor.

 

[Carultch]

1A is incorrect. Any neutral current is current not being carried by a line conductor.

What I mean, is the circuits that are built with the 1-pole breaker off the panelboard. There is no other option than for the current to return to the panelboard on the neutral. I'm not talking about the feeder to this panelboard, but rather the branch circuit.

3 identical of such branch circuits that are distributed among the phases, will have zero neutral current on the feeder supplying their panelboard. However each individual 1-pole branch circuit will still have a neutral current. The neutral currents add up as vectors to zero, prior to branching.

 

[roger]

Along with that, 1B and 2 are only applicable to a wye, not a delta.

Roger

 

[roger]

What I mean, is the circuits that are built with the 1-pole breaker off the panelboard. There is no other option than for the current to return to the panelboard on the neutral. I'm not talking about the feeder to this panelboard, but rather the branch circuit.

3 identical of such branch circuits that are distributed among the phases, will have zero neutral current on the feeder supplying their panelboard. However each individual 1-pole branch circuit will still have a neutral current. The neutral currents add up as vectors to zero.

You meant to say two wire branch circuits then.

Roger

 

[Carultch]

You meant to say two wire branch circuits then.

Roger

The term I used, means the same thing, does it not? "single phase line-to-neutral circuits "

 

[roger]

The term I used, means the same thing, does it not? "single phase line-to-neutral circuits

" Kinda but MWBC's can also be considered line to neutral circuits.

Roger

 

[kwired]

Generally the answer is no, but here are two reasons why the answer would be yes:

1: If neutral is a mandatory part of the return path of the circuit, even for balanced loads, you count it.

Examples being:
A. single phase line-to-neutral circuits (this one is obvious)
B. the feeder derived from a pair of phases & neutral of a 3-phase system, that serves phase-to-neutral loads. Due to the fact that the phases are not equal and opposite, the neutral will still carry current even when these are balanced.

2. If the system has non-linear loads with significant harmonics, then you count it. Triplen harmonics on three phase in particular, will add up, instead of cancel. Or similarly, even harmonics on split-phase.

Bold part maybe needs a little work? Maybe not exactly wrong but can be misunderstood somewhat easily. Neutral is mandatory in a MWBC, even if balanced loads. Loads might work without it but at very least it does help assure those loads see proper voltage.
Single phase 120/240 MWBC yes it may not be as critical, put same loads on two lines and neutral of a 208/120 and if you eliminate the neutral you force volts across balanced loading to drop to 104 and 104 vs 120 each.