[RE-wrenches] Very unbalanced DC wiring

[Nathan Stumpff]

Wrenches,

I am doing a job for a customer installing a ground mounted array about 250' from his existing battery bank. Array is:

-          Vmp: 87.9 V

-          Imp: 47.1 A

-          Classic 150 controller

The customer already owns (hence the choice of the 150 over the 200 or 250 controller) sufficient length for the array transmission of a heavy duty direct burial rated cable, 3 (total) conductor 3/0 AWG copper. He also happens to own sufficient length of #2 AWG USE-2 copper.

My question is: is there a problem (code or practical or both) with using two of the 3/0 conductors paralleled for either the positive or negative, and one of the 3/0 conductors by itself for the other side? In this case I would use the USE-2 as the grounding jumper.

The max voltage drop on the circuit using only single conductor 3/0 over this distance (and also accounting for stepping down the conductor size and array circuit conductors, etc.) is about 2.5% max, so we could live with this. That said, the customer already owns all of this wire and if I can safely shave a couple tenths of a percent voltage drop, every bit helps when you are off grid.

It seems to me that using doubled cable on one side only is effectively exactly the same as having home run cables (of the same AWG) from a series strings of modules where either the positive or the negative is twice as long as the other, which happens all the time at the array.

Any thoughts most appreciated!

-Nathan

--
Nathan J. Stumpff - Arctic Sun, LLC
NABCEP Ceritified PV Installer #091209-175
NABCEP Certified Solar Heating Installer #032412-14
nathan at arcticsun-llc.com<mailto:nathan at arcticsun-llc.com>
Office: 907/457-1297
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