Neutral Wire Size

[Franco]

Hello, I am putting up a 48 panel system at my home and having trouble determining what size neutral wire I need. The array is 350 feet from the main panel. I am using enphase inverters with schott panels. I will be installing a subpanel at the array which will then go to the ac disconnect at the main panel. I plan on upsizing the wire to (2) 2/0 copper to account for voltage drop. On my initial plans I put down #4 awg for the ground but didn't specify the neutral. Can I get away with using #4 for the neutral or does it have to be same size as the two hots? Thanks.

[Mike90250]

Are the enphase inverters 120V or 240V ?

If 120VAC, and you balance them evenly across phases, you can only go 1 gauge smaller than the 2 hot phases gauge (If I recall this rightly) .

If they are 240VAC, there would be no / zip / nada amps flowing in the neutral, and you could use as small as code would allow.

And if I'm too tired to recall correctly, someone will correct me.

[RCinFLA]

The only thing the neutral is used for on Enphase microinverters is the condition check for split phase voltage. Very little current appears on neutral.

By UL1741, the inverter must disconnect if either hot to neutral voltage is below 88% of the nominal (120v) line-to-neutral voltage (Vnom). For the 240vac inverter, all the power is pushed between the 240vac L1,L2 lines. Only voltage sense monitoring is done between L1, L2 and neutral.

If it was not for this UL requirement there would be no need for neutral line.

Functionally, 14 gauge would be more then sufficient but sometimes local inspectors expect equal to no less then two gauges below L1, L2 gauge, just because neutral wire is there. Check with your local code. I know of one situation where local code inspector required white neutral wire to be same gauge as L1, L2 line but was satisfied with changing the neutral return from micro-inverters to yellow #14 wire and calling it a safety control line, which is what it really is.

[Naptown]

As said above and to add that the neutral wire is for communications for the monitoring in that system

[Franco]

Thanks for the input. I like the idea of changing the wire color if the inspector permits it. No need to have a large gauge neutral that only serves as a communication wire.

[Sunking]

Code is very specific with respect to grounded circuit and ground conductors. Take your pick of the 3. I suggest WHITE a sit is default standard every inspector is looking for. To your specific application:


200.6 Means of Identifying Grounded Conductors.

(A) Sizes 6 AWG or Smaller. An insulated grounded conductor
of 6 AWG or smaller shall be identified by a continuous
white or gray outer finish or by three continuous
white stripes on other than green insulation along its entire
length. Wires that have their outer covering finished to
show a white or gray color but have colored tracer threads
in the braid identifying the source of manufacture shall be
considered as meeting the provisions of this section. Insulated
grounded conductors shall also be permitted to be
identified as follows:

(1) The grounded conductor of a mineral-insulated, metalsheathed
cable shall be identified at the time of installation
by distinctive marking at its terminations.

(2) A single-conductor, sunlight-resistant, outdoor-rated
cable used as a grounded conductor in photovoltaic
power systems as permitted by 690.31 shall be identified
at the time of installation by distinctive white
marking at all terminations.

(3) Fixture wire shall comply with the requirements for
grounded conductor identification as specified in 402.8.

(4) For aerial cable, the identification shall be as above, or
by means of a ridge located on the exterior of the cable
so as to identify it.