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Old 04-18-17, 04:14 PM   #2
Steve Hull
Join Date: Dec 2012
Location: hilly, tree covered Arcadia, OK USA
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Well, lets calculate . . . .

You have some 600 sq feet of roof size (20 x 30 ft). Assume you fill the roof completely with panels with each panel being about 18 sq feet each. About 33 panels (600/18).

Assume net output of 300 watts (high estimate per panel ) gives you about 10 kW (300 W x 33). P = Ei so the wattage is about 40 amps at 240 V.

Now the kicker is how far your wire run is. This current load is likely going to need 6 G stranded copper (NOT aluminum) and maybe 4G if it is a long run (> 75 feet).

Remember that L1 and L2 (each being the 120 V legs) need to be fat and thick (6 or 4 G). The neutral can be 8 or even 10G with 10 G for the ground (four wires total). The extra $ cost for thicker G wire is small considering safety and lower voltage drop .

I would use 1 inch conduit with a pull string installed. The above four wires can easily fit in this size conduit.

GREAT idea to do this now. Also excellent roof pitch for your latitude.

Hope this helps.

consulting on geothermal heating/cooling & rational energy use since 1990

Last edited by stevehull; 04-18-17 at 04:23 PM.. Reason: clarity
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