wire and ground

Posted by Rene M on September 10, 2008, 07:17:26 AM

would it work OK to use house wire 12/3
to hook panels
black negative
red positive fused
green ground the system frames etc.
or would the system ground be too small a wire
Rene

Posted by Thomas Allen Schmidt on September 12, 2008, 12:31:54 PM

Re: wire and ground (Reply #1)

It would work but, only under certain circumstances might this be legal. It is not recommended. It could even be considered illeagle by the NEC (National Electrical Code.)

#12 Romex (Romex is a trade name of wire that a lot of people associate with the type of wire you are referring to. Like Sheetrock is a trade name of drywall or gypson board.) has a rating of only 20 amps at 250 volts, it is not rated for the temperatures associated with PV arrays, it is not outdoor rated, and it is not rated to be "strapped" directly to metal, and it cannot be used inside of a conduit from box to box, although it can leave a box in conduit and exit the other end of that conduit into wood framing.
If it were to leave the PV modules J-box in conduit and penetrate the roof where it could then exit the conduit and be stapled to wood, it might pass an inspection. There is still the amperage and temperature ratings to consider.
(In my opinion, the temperatures at the PV module (167 degrees F) are not that different to the temperatures in an attic space (140 degrees F.) This is where your local electrical inspector would have to make the final decision.
Here is a link to acceptable wire for PV array source circuits.
http://photovoltaics.sandia.gov/docs/John_Wiles_Code_Corner.htm
Note that the NEC is revised every three years. The lastest is the 2008 Code.
http://www.nfpa.org/catalog/product.asp?pid=7008SB&order_src=A291
Also available at your local electrical supply house.
If I might, make a suggestion? Make friends with an electrician? They are not that bad of people once you get to know them. Some electrical contractors can be real prima donna's though, but then, can't we all from time to time?

Posted by Ken Hall on September 13, 2008, 01:32:55 PM

Re: wire and ground (Reply #2)

What is the distance (by the wire route) between your panels and your batteries ?
What percentage voltage drop are you shooting for ?

The #12 may be too small.

You should be looking at stranded wire, not solid.

Posted by Rene M on September 13, 2008, 08:22:24 PM

Re: wire and ground (Reply #3)

Stranded like in automotive wire or ac power wire
Between panel and battery the distance is around 15 ft to 18 ft.,14 gauge ,12 or 10gauge Huh

?
50 watt panel 3 amps.
But will be adding on to increase amps.lets say up to 15 amps.
Rene

Posted by Ken Hall on September 14, 2008, 11:45:37 AM

Re: wire and ground (Reply #4)

You need to use the short circuit amperage, which I believe is 3.35 for your panel. Then multiply by 1.56. So the following is based on 5.226 amps per panel.

You are OK on #12 for the one panel.
If you are going expand to 5 panels, you will be looking at either a #6 or #4, depending on the exact distance.

I would use what you are calling "ac power wire".

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