ungrounded system with thwn-2 for DC feeders

[natron chief]

PV wire must be used for ungrounded systems instead of USE-2. Normally after transitioning from a combiner or junction box I run THWN-2 in conduit to complete the DC run to the inverter. Is that ok or must I use PV-wire all the way back even if in conduit? it comes in various sizes, but the big sizes are hard to find.

http://www.graybar.com/documents/encore-wire-pv-wire.pdf

 

[ggunn]

PV wire must be used for ungrounded systems instead of USE-2. Normally after transitioning from a combiner or junction box I run THWN-2 in conduit to complete the DC run to the inverter. Is that ok or must I use PV-wire all the way back even if in conduit? it comes in various sizes, but the big sizes are hard to find.

http://www.graybar.com/documents/encore-wire-pv-wire.pdf

In conduit you can use THWN-2. It's only where the wire is outside conduit that it needs to be PV wire. Some TL inverters are bipolar as well, with two subarrays in series. In those cases you will need to keep the conductors from the upper array isolated from those from the lower array.

 

[GoldDigger]

In conduit you can use THWN-2. It's only where the wire is outside conduit that it needs to be PV wire. Some TL inverters are bipolar as well, with two subarrays in series. In those cases you will need to keep the conductors from the upper array isolated from those from the lower array.

Or use higher voltage insulated wire, such as PV-1000 or the anticipated PV-2000. Because of the testing requirements of the NEC and UL you cannot get single-listed non-PV wire with an accepted insulation strength over 600V.

 

[ggunn]

Or use higher voltage insulated wire, such as PV-1000 or the anticipated PV-2000. Because of the testing requirements of the NEC and UL you cannot get single-listed non-PV wire with an accepted insulation strength over 600V.

FWIW, Refosol (now part of AE) still recommends separating the upper and lower array conductors even with PV-1000.

 

[GoldDigger]

FWIW, Refosol (now part of AE) still recommends separating the upper and lower array conductors even with PV-1000.

Depends on the array voltage. The standard seems to be to use N-volt rated insulation on both wires whenever the potential difference between them is (or might be) N volts. Even though a fault would have to go through two layers of insulation.

I would not recommend PV-1000 wire for a bipolar array with sub-array voltages above 500VDC. That is why I also mentioned PV-2000 wire which is currently offered by Southwire. Made with bi-polar arrays in mind, I think.