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zman22 11-09-2011 02:42 PM

Solar panels 3 gauge wire ***Correction 4 GAUGE
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Hi, I have a question about my solar panel array. I originally installed a 42 panel array ground mounted about 140 feet from my house were it's connected to the grid. The wire we ran in the ground from the array inverter to the home electrical panel is 3 gauge wire. Now I want to add an additional 12 panel array near the same loaction.

Question: Can I use the existing 3 gauge run, install an electrical panel out by the original 42 panel array and connect breakers from both array inverters to the new electrical panel ? In other words, can I use the same wire or do I need to run a new run to my house ?

A) 42 panel array = 7980 watts (currently installed)
inverter max = 7000 watts

B) 12 panel array = 2640 watts inverter max = 2500


zman22 11-09-2011 03:00 PM

Forgot to add that the inverter output is 220 :)

Speedy Petey 11-09-2011 03:13 PM

IMO solar is NOT a DIY type project.

Are you a solar or electrical engineer? From the question I have to assume not.
What is your background?

If my calculations are right, and I doubt they are as I know nothing about solar, I get 10,620 watts. This @ 240v, @ 140' from the house, is around 45 amps @ 240v.
The #3cu is WAY overkill even for both sets of panels, even at that 140'.

carmusic 11-09-2011 03:14 PM

should be ok it is not even 50 amp but i dont think you can connect 2 inverters output in parallel unless specified

mpoulton 11-09-2011 03:39 PM

It depends on the inverters. If they are both grid-tie inverters and you're selling power back to the power company, then you should be able to do this with no problem. The inverters will both sync to the grid and deliver their power appropriately. If this is not a grid-interconnected system (i.e. you have a battery bank, inverter/charger combination, or other arrangement) then you probably can't parallel the inverters because they will not synchronize. Definitely read the inverter manuals to see what they say about multi-inverter systems.

forresth 11-09-2011 05:32 PM

3 gauge copper is good for something like 150 amps I believe.

150 amps x 220volts = 33,000 watts.

I'd say you can add a few more panels still before you start melting wires :wink:

zman22 11-09-2011 06:12 PM

Thanks for all the replies. Yes, both Sunny Boy inverters are grid tie types. Basically I decided to build the 42 panel array 3 years ago when the incentive was at 3.75 per watt but I did not take advantage of the entire 10K watts of rebates. I am not an electrical engineer. Just a very competent guy with electric who has a computer science degree and a couple of electronic technology diplomas. The Town will ultimately approve or not approve the second system the way I want to do it, but I figured there was no better place to ask first than here.
BTW: The entire project was definitely a DYI in my opinion. Building a glorified 35 degree deck to mount the panels wasnt too difficult, wiring was simple, and connecting to the grid was a simple procedure of adding a breaker to your panel. Designing it is for the pros. hehe
Again thanks for the re-assurance everyone. Oh and, Overkill is my middle name. LOL:laughing:

zman22 11-09-2011 09:47 PM

Correction. The run to the house from the inverter is 4 gauge. A friend is telling me that the voltage drop is the main issue. Should this be a concern now with 4 gauge wire and voltage drop calculated in for a 140 foot run ???:huh: This is the hard part to understand. THANKS

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