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Old 01-14-14, 10:04 AM   #11
pinballlooking
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The microinverters talk across the neutral wire. The inspector will want the wires in the same gauge in conduit (as stated above)
Check out these two projects.

My utility company requires a disconnect switch right by the meter so check with yours and see if they require that. if so adjust your wiring plan.


Designing and Installing a Grid-Tie PV System Designing and Installing a Grid-Tie PV System
http://www.builditsolar.com/Projects...asePV/Main.htm

Doug's New 4.6 KW micro inverter DIY Grid Tied PV Array
http://www.builditsolar.com/Projects...ougEnphase.htm

Here is my 12.5 kw self-install.
http://ecorenovator.org/forum/solar-...lar-array.html


Last edited by pinballlooking; 01-14-14 at 10:10 AM..
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Old 01-14-14, 03:01 PM   #12
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Thanks to all for the helpful answers. Right now I'm planning on 14 60 cell panels. That's so close to the maximum number on a circuit I'll just plan on wiring for the maximum (for expansion later), which works out to 10 gauge for a 60 ft run. That was useful information about the neutral wire only taking 5 percent of the current normally in this application. I didn't know that.

Right now I'm tempted to just get some armored shielding and anchor one end under the roof at a box and run it out the roof. Then I would just run 10 ga romex through it and terminate the other end at the pv central junction box. I know that legally you are required to not run unspliced wires through boxes. And the box under the roof where the armor is attach certainly wouldn't need to have the wires cut and rejoined. It would be better NOT to do that electrically. We'll see.

I haven't gotten to look at those references you put up, Pinballooking, but I look forward to soon.
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Old 01-14-14, 04:27 PM   #13
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I believe the NEC allows for unspliced wires to pass through a box provided that enough slack is left in the box so that a splice can be made in the future if needed. (Basically a "service loop")
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Old 01-15-14, 02:27 AM   #14
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I'm realizing that I'm not communicating very well my problem with where the homerun cable exits the roof. I'm sure there is a standard solution out there because everyone with PV on their roof and the power connecting first at/near the house main CB panel would require it.

There has to be one of the following two solutions:

1.A roof flashing for this purpose that is rainproof and lets bare cable exit the roof. In this case the cable would have to be UV resistant. If people use this solution then what is the flashing they use and what type of sheathed cable is UV resistant?

2.A rainproof flashing similar to above that has a connection to attach a conduit of some sort. The conduit would then attach between this flashing and the PV central box right at the parallel distribution point of the PV panels.

EDIT:
Just found a solution and it will work far better than what I was thinking of. It is a flashed pass-through box that will allow me to terminate the homerun cable right at the box and lets me connect wiring from the panels at a later date. Much easier for me than putting in cable in one piece and trying to adjust the length later, not to mention cutting conduit with wiring inside and managing not to nick the wires. That would be almost impossible.

http://webosolar.com/store/en/boxes-...e-0786-3r.html

Last edited by Exeric; 01-15-14 at 02:55 AM.. Reason: Found a solution
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Old 01-15-14, 06:52 AM   #15
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If you are going to run a 3kw system, and are using Enphase M215 inverters, you will only need to run a 14/3 wire plus your #6 ground wire for the racking (assuming your code requires it and AFAIK they all do). Each inverter will output a max of 0.9Aac so with a 250w panel you will have 12 x .9A x 1.25 (safety factor) = 13.5A. You will need to go to a 15A double pole breaker.
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Old 01-16-14, 02:18 PM   #16
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Quote:
Originally Posted by Mikesolar View Post
If you are going to run a 3kw system, and are using Enphase M215 inverters, you will only need to run a 14/3 wire plus your #6 ground wire for the racking (assuming your code requires it and AFAIK they all do). Each inverter will output a max of 0.9Aac so with a 250w panel you will have 12 x .9A x 1.25 (safety factor) = 13.5A. You will need to go to a 15A double pole breaker.

I've been thinking about this and I just don't think this is close to right. I think you are leaving out something big - voltage drop/foot per gauge of wire.
Also you have to multiply 60' x 2 = 120' for up and back total length of homerun wire times that resistance. Also, though I didn't say it, I intend to have no more than a 1% V drop from the 240volts = 2.4 V. Finally, my plan is to have 14 panels not 12, which I think I stated. The .9A x 1.25 is correct.

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Old 01-16-14, 02:53 PM   #17
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Here is the calculations for 10 and 14 AWG:

10awg resistance = 120' x .001 ohm/foot = .12 ohms
current = .9 x 14 x 1.25 = 15.75 amps
Voltage drop = I x R = 15.75 amps x .12 ohms = 1.89 Volts < 2.4V

14awg resistance = 120' x .0025 ohm/foot = .3 ohms
current = .9 x 14 x 1.25 = 15.75 amps
Voltage drop = I x R = 15.75 amps x .3 ohms = 4.75V > 2.4V

Also, I could max out to 17 microconverters at a later date on that line and still be under 1 % voltage drop ,i.e. 2.4 volts. It looks like I need 20A double ganged circuit breakers.

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Old 01-16-14, 03:27 PM   #18
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Voltage Drop Calculator

Heres a link that you may find helpful on voltage drops.

Unless your dead set and already have the pannels i would run the conduit for now Maybe a bit bigger sized thats up to you though . Dont know about you but i hate having to pull a heavy guage wire through a conduit thats almost to small
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Old 01-16-14, 04:14 PM   #19
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I've been a bit perplexed about why one would use conduit INSIDE the house for roof top mounted PV. I'm guessing that it's needed and is a holdover from non micro inverter grid tied systems. You are working with high DC voltages there and it might be good to protect those wires more than others. For me, romex works just fine for micro inverter systems. The only place I plan to have conduit is between this

SolaDeck Roof Mount Passthrough Enclosure, 0786-3R

and the central junction box right at the panels, about 3 feet or less if I plan it right. I can use a smaller gauge romex for that short length.
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Old 01-16-14, 04:35 PM   #20
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I just used the voltage drop calculator but used 60 ft instead of 120 ft. It looks like it does that doubling internally. Got the same answer and recommendation I came up with -10awg. It works.

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