Does neutral of microinverter

[inspector23]

Does the neutral of a microinverter count as a current carrying conductor for ampacity adjustment per 310.15[4][a]? (2008NEC).

Contractor has ten #12awg conductors in one conduit [combiner to subpanel]. If counted as a CCC's, then I have to adjust by 50%. If they do not count as CCC's, then I only have 5 CCC's and only adjust by 80%, Still have to deal with the rooftop adder adjustment, but I want to claify this first before I make any more adjustments. My thinking is they do count, as they are AC and they complete the circuit, but I doubt myself as I am in unfamiliar territiory plan checking and want to be sure.

Thanks in advance for your help.

My memory is going the way of my toes - I don't see either of them much anymore!

 

[Zee]

Good Q.

In 11 years, I have never counted them as CCC's for 240 VAC inverters as they are dedicated circuits , where - IMHO - the neutral serves only the purpose of sensing any voltage imbalance (just to ensure that the 220 VAC is evenly balanced across the two hot legs ).
(Actually, i remember, for years, no neutral was even run to the inverters as they had no terminal for neutral!)

But you mention 5 hot wires out of 10....so are these in fact 120 VAC microinverters? IN that case neutrals are definitely CCC's.


If not:
I assume the 10 conductors are in fact 6 hot, 3 neutrals and 1 ground. In that case: worst case scenario 9 ccc's ====>70% derate. (instead of 10 CCC's = 50%)

 

[GoldDigger]

Good Q.

In 11 years, I have never counted them as CCC's for inverters as they are dedicated circuits , where - IMHO - the neutral serves only the purpose of sensing any voltage imbalance (just to ensure that the 220 VAC is evenly balanced across the two hot legs ).
(Actually, i remember, for years, no neutral was even run to the inverters as they had no terminal for neutral!)

But to bypass the point and make a guess......
I assume the 10 conductors are in fact 6 hot, 3 neutrals and 1 ground. In that case: worst case scenario 9 ccc's ====>70% derate. (instead of 10 CCC's = 50%)

General rules:
If the output of each micro inverter is 220 volt split phase, the neutral will not be current carrying.
If the output of each micro inverter is a single phase-to-phase pair of a 3-phase circuit, the neutral will not be carrying current, regardless of what your phase balance is.
If the output of each micro is 120 volt phase to neutral in either a split-phase or three phase system (and I do not know of any like that) then the neutral may be current carrying, but only to the extent that the phase currents are unbalanced and so any neutral current will be compensated for by a reduction in one or more line currents.
Summary: You do not need to count it as current carrying for this purpose, even though it may be carrying current.

 

[Smart $]

...
If the output of each micro is 120 volt phase to neutral in either a split-phase or three phase system (and I do not know of any like that) then the neutral may be current carrying, but only to the extent that the phase currents are unbalanced and so any neutral current will be compensated for by a reduction in one or more line currents.
Summary: You do not need to count it as current carrying for this purpose, even though it may be carrying current.

It is really simple for 120V microinverters. Where two-wire, the neutral counts as a CCC. Where combined to form a three-wire (split phase) or four-wire (208V/120 3? wye) circuit, the neutral would not be counted as a CCC. On the odd chance someone wires the inverters to make a 120/208V 1? 3W circuit, the neutral would count.

 

[jaggedben]

On the odd chance someone wires the inverters to make a 120/208V 1? 3W circuit, the neutral would count.

How about if someone wires, say, 14 inverters that are each on on a 120/208V 1? 3W circuit, with 5, 5, and 4 on each phase respectively?

Reason I ask is because this is exactly how Enphase's 208V system works.

 

[Smart $]

How about if someone wires, say, 14 inverters that are each on on a 120/208V 1? 3W circuit, with 5, 5, and 4 on each phase respectively?

Reason I ask is because this is exactly how Enphase's 208V system works.

Now that you bring it up, I'm thinking I got ahead of myself and forgot to consider the possibility the inverters are only using it for voltage and voltage phase angle purposes and not as a current carrying conductor.. as others have stated.

Thinking on that a little more, that may be true for the circuit on the whole, but what about the neutral conductor in between inverters? You can't have current on an inverter's hot without current on it's neutral... and that current has to go to the opposing phase inverters' neutral and back out through its hot.

Take the 4 inverter string as an example. Say the string is conducting 10A of A-B phase current. 5A through each inverter's hot. How does the current get from A-line inverters to the B-line inverters?

And thinking on it a little more, the same would be true for split phase and 3? wye 4W...

So it all depends on where in the circuit we are talking about.

 

[GoldDigger]

Now that you bring it up, I'm thinking I got ahead of myself and forgot to consider the possibility the inverters are only using it for voltage and voltage phase angle purposes and not as a current carrying conductor.. as others have stated.

Thinking on that a little more, that may be true for the circuit on the whole, but what about the neutral conductor in between inverters? You can't have current on an inverter's hot without current on it's neutral... and that current has to go to the opposing phase inverters' neutral and back out through its hot.

Take the 4 inverter string as an example. Say the string is conducting 10A of A-B phase current. 5A through each inverter's hot. How does the current get from A-line inverters to the B-line inverters?

And thinking on it a little more, the same would be true for split phase and 3? wye 4W...

So it all depends on where in the circuit we are talking about.

If the neutral is not used as a current carrying conductor, the three different inverter groups will be wired line A to line B, B to C, and C to A. None of those require any current to flow in the neutral, but you want to spread them out equally if possible since otherwise the line current will be higher than it needs to be in the interconnecting wires of the harness. There is no reason that you cannot have unbalanced line currents in a delta.

If the inverters are all wired line to neutral, then there will be varying neutral currents at different points in the harness.

 

[jaggedben]

To clarify, my understanding was that no solar inverter puts current on the neutral unless it is wired L-N. (That is notwithstanding tiny amounts of current for power-line communication.)

I only know of one brand of microinverter that would connect L-N, and it was discussed in this thread.

 

[Q-5 Hunter]

Take the 4 inverter string as an example. Say the string is conducting 10A of A-B phase current. 5A through each inverter's hot. How does the current get from A-line inverters to the B-line inverters?

Hi Smart $. I have read this statement a few times to make sure I am understanding you correctly since it looks like everyone has a handle on the non-CCC of the micro inverters, although I don't know of any 120V micros that are worth mentioning.

However, when an inverter's maximum output current is, for example, 10A, that is the current rating produced on each hot- not 5A per line. Like I said, I hope I am misunderstanding your statement, but when calculating OVP for inverters it is maximum current rating X 1.25 and not 1/2 * max current X 1.25.

 

[Smart $]

Hi Smart $. I have read this statement a few times to make sure I am understanding you correctly since it looks like everyone has a handle on the non-CCC of the micro inverters, although I don't know of any 120V micros that are worth mentioning.

However, when an inverter's maximum output current is, for example, 10A, that is the current rating produced on each hot- not 5A per line. Like I said, I hope I am misunderstanding your statement, but when calculating OVP for inverters it is maximum current rating X 1.25 and not 1/2 * max current X 1.25.

When I mentioned 10A on each hot, 5A through each inverter, had no relation to inverter output rating... simply 10A on each hot at that instance would likely be divided 5A each amongst the 4 connected L1-N-L2.

 

[Smart $]

...

If the inverters are all wired line to neutral, then there will be varying neutral currents at different points in the harness.

...and there you have it.