Solar panel wiring

Just run the wire for the most amps you dream of having. #4 would be great.

Thank you all for your answers.

pianotuna wrote:
Just run the wire for the most amps you dream of having. #4 would be great.

er no, you don't need 4 AWG

I have 960 W on my roof ( 6 * 160 W ) configured as 3S2P and the max current is 17 Amps @ 54 V, 10 AWG is more than enough.

Vdrop over 40Ft of 10AWG at 17 A is less than 1V.

if you think you need 4 AWG then you need to think again..
unless you have cash to burn..

OldSmokey wrote:

pianotuna wrote:
Just run the wire for the most amps you dream of having. #4 would be great.

er no, you don't need 4 AWG

I have 960 W on my roof ( 6 * 160 W ) configured as 3S2P and the max current is 17 Amps @ 54 V, 10 AWG is more than enough.

Vdrop over 40Ft of 10AWG at 17 A is less than 1V.

if you think you need 4 AWG then you need to think again..
unless you have cash to burn..

I don't think you've calculated the voltage drop correctly. I'd bet you are dropping voltage 3-4% over 40' of 10 ga at 54V w/17 A.

A better practice may be to install the largest wire possible from the roof to the controller location. That will insure that all the current produced gets to the controller.

Without knowing the OP's plans, use, and dimensions, it is difficult to advise a wire gauge. I always tend to install larger wire as the price is not significant and I will be sure it is large enough to handle the loads.

westend wrote:
I don't think you've calculated the voltage drop correctly. I'd bet you are dropping voltage 3-4% over 40' of 10 ga at 54V w/17 A.

A better practice may be to install the largest wire possible from the roof to the controller location. That will insure that all the current produced gets to the controller.

yeh.. I messed up, I'm tired and have had a few beers..
here is the revised calculations.

The resistance per foot from the standard AWG tables is 0.9989 milliOhms per foot for 10AWG copper.
my panels Vmpp is 18.8 V and I have approx 40 foot run inclusive from panels to charge controller.
so assuming I could actually get 160W from each panel on a perfect day then: as a 3S2P string I get 18.8V*3 = 56.4 Volts from each string. (160W*3)/56.4V = 8.51 Amps. with 2P = 8.51*2 = 17.02 Amps
therefore: 40ft * 0.0009989 Ohms * 17.02 Amps = 0.68005 Volts drop
0.68005/(56.4/100) = 1.2%

you lost the bet.:p