Wire size (and type) for 522V, 9A panel strings in 100 feet of PVC conduit?

[wpns]

I've got some panels (38Voc, 9Asc) in 3 strings of 15 panels each, so 570Voc and 9Asc. They currently go into a DC combiner at the array and run about 100 feet into a single-MPPT inverter, so 570Voc and 27Asc.

Now I want to feed the array into two separate parallel inverters, 2 strings in parallel into one inverter and one string into another.

The 2" (grey, electrical) PVC conduit from the array to the inverter(s) location has four 6AWG THHN wires (red and black for the combined DC voltage, green for ground, and a white spare.

I've also got 4-500 feet of 14AWG THHN wire on-hand in red and black. And a few questions:

1) Is 600V THHN wire good for 570Voc strings? They normally run <lessee> in the 400V range, and the max I've logged is 522V, so I'm assuming I'm OK? [They do not currently have RSD devices, but those are on-order, so I'm not imagining we'll ever see peak voltages. Historical low temperature was 62F overnight, so not expecting anything higher, especially in the daytime.]

2) Is 14AWG THHN OK for 9Asc strings? The voltage calculators I've seen seem to think I'll lose on the order of 1%, which is fine, but the YouLoveSolar spreadsheet seems to indicate I should use 4AWG wire, so I'm probably doing something wrong setting it up. Ampacity of 14AWG THHN is 25A, so I can't imagine melting the wires...

2) How should I wire everything? I'm assuming I'll have to pull the four 6AWG wires out of the conduit, add or subtract some wires, and pull it back. I'm not positive the existing wires are long enough to get to the new inverter location, can I extend the 6AWG wires with waterproof butt splices? Should I just remove everything and run (the 6AWG ground plus) three pairs of 14AWG red and black wires, one from each string, so I can easily swap strings to different inverters in the future?

Thanks!

 

[timselectric]

I've got some panels (38Voc, 9Asc) in 3 strings of 15 panels each, so 570Voc and 9Asc. They currently go into a DC combiner at the array and run about 100 feet into a single-MPPT inverter, so 570Voc and 27Asc.

Now I want to feed the array into two separate parallel inverters, 2 strings in parallel into one inverter and one string into another.

The 2" (grey, electrical) PVC conduit from the array to the inverter(s) location has four 6AWG THHN wires (red and black for the combined DC voltage, green for ground, and a white spare.

I've also got 4-500 feet of 14AWG THHN wire on-hand in red and black. And a few questions:

1) Is 600V THHN wire good for 570Voc strings? They normally run <lessee> in the 400V range, and the max I've logged is 522V, so I'm assuming I'm OK? [They do not currently have RSD devices, but those are on-order, so I'm not imagining we'll ever see peak voltages. Historical low temperature was 62F overnight, so not expecting anything higher, especially in the daytime.]

2) Is 14AWG THHN OK for 9Asc strings? The voltage calculators I've seen seem to think I'll lose on the order of 1%, which is fine, but the YouLoveSolar spreadsheet seems to indicate I should use 4AWG wire, so I'm probably doing something wrong setting it up. Ampacity of 14AWG THHN is 25A, so I can't imagine melting the wires...

2) How should I wire everything? I'm assuming I'll have to pull the four 6AWG wires out of the conduit, add or subtract some wires, and pull it back. I'm not positive the existing wires are long enough to get to the new inverter location, can I extend the 6AWG wires with waterproof butt splices? Should I just remove everything and run (the 6AWG ground plus) three pairs of 14AWG red and black wires, one from each string, so I can easily swap strings to different inverters in the future?

Thanks!

If you already have 14 gauge wire. I would run each string separately. This gives you the ability to change your configuration in the future if you want to. Without having to replace wiring, again.
If you decide to go with 2 and 1 string. I would recommend #12 for the 2 combined strings.
For 3 separately ran strings, #14 is fine for the EGC.
If you go with 2 and 1, I would recommend #12 for the EGC.
These are all minimum sizes. You can always go larger if you want.