system grounding questions

umm,

normally we would assume that the combiner is outside, right next to the array.

when this is the case, you bring out of the combiner, one positive, one negative, one equipment ground conductor.  they all leave the area of the modules in conduit, and come inside to the dc load center (usually stuff like in the links below)

http://store.altenergystore.com/Enclosures-Electrical-and-Safety/Electrical-Enclosures/DisconnectLoad-Enclosures/Dc/Outback-FlexWare-FW500-DC-breaker-enclosure/p5576/

http://store.altenergystore.com/Enclosures-Electrical-and-Safety/Electrical-Enclosures/DisconnectLoad-Enclosures/Dc/Xantrex-Dc250-250A-125Vdc-Disconnect-WEncl/p2086/

when this is the case, you would then EITHER
bond the negative busbar to the grounding busbar to make the system negative grounded.  OR you would follow the directions of your GFP device if your modules were mounted on a building.

in either scenario the wire that goes from that enclosure to the ground rod (in proper terms - grounding electrode conductor to grounding electrode) would come from the dc load center (see links above). 

you may also drive a secondary ground rod for your array and that would come from the combiner, but you would not bond from the negative to ground.

lastly if you had a pole mount system that was really far away from your dc load center, you could drive a secondary ground rod for the array and pole, only carry negative and positive back to the house, but the dc load center and metal enclosures inside would have their own equip grounding conductors, grounding electrode conductors, and grounding electrode.  john wiles wrote a great code corner article on this called "grounding the south 40"

i forgot you were in chicago, i was just in town, taking care of the last bits with comEd to get my mom's pv system running. 

james
altE staff

found this nice grounding description at Affordable Solar. It appears that I just need to ground the frames and equip boxes to one ground rod and then attach the battery neg to another about 10'-0" away if need be.

Sorry for all the bandwidth about grounding. I just think it would be silly to get a hold of an electrician just to ground a 100watt 12v system...I'm sure I can figure this out eventually.

Maybe altE should have a specific ONLINE course in grounding..hint hint:)

To achieve effective grounding FOLLOW THESE GUIDELINES:

INSTALL A PROPER GROUNDING SYSTEM:

Minimal grounding is provided by a copper-plated ground rod, usually 8 ft. long, driven into the earth. This is a minimum proceedure in an area where the ground is moist (electrically conductive). Where the ground may be dry, especially sandy, or where lightning may be particularly severe, more rods should be installed, at least 10 feet apart. Connect or "bond" all ground rods together via bare copper wire (#6 or larger, see the NEC) and bury the wire. Use only approved clamps to connect wire to rods. If your photovoltaic array is some distance from the house, drive ground rod(s) near it, and bury bare wire in the trench with the power lines.

Metal water pipes that are buried in the ground are also good to ground to. Purchase connectors approved for the purpose, and connect ONLY to cold water pipes, NEVER to hot water or gas pipes. Beware of plastic fittings -- bypass them with copper wire. Iron well casings are super ground rods. Drill and tap a hole in the casing to get a good bolted connection. If you connect to more than one grounded object (the more the better) it is essential to electrically bond (wire) them to each other. Connections made in or near the ground are prone to corrosion, so use proper bronze or copper connectors. Your ground system is only as good as its weakest electrical connections.

If your site is rocky and you cannot drive ground rods deeply, bury (as much as feasible) at least 150 feet of bare copper wire. Several pieces radiating outward is best. Try to bury them in areas that tend to be moist. If you are in a lightning-prone area, bury several hundred feet if you can. The idea is to make as much electrical contact with the earth as you can, over the broadest area feasible, preferably contacting moist soil.

You can save money by purchasing used copper wire (not aluminum) from a scrap metal dealer, and stripping off the insulation (use copper "split bolts" or crimped splices to tie odd pieces together. If you need to run any power wiring over a distance of 30 feet or more, and are in a high-lightning, dry or rocky area, run the wires in metal conduit and bond the conduit to your grounding system.

WHAT TO CONNECT TO YOUR GROUND SYSTEM:

GROUND THE METALLIC FRAMEWORK of your PV array. (If your framework is wood, metalically bond the module frames together, and wire to ground.) Be sure to bolt your ground wires solidly to the metal so it will not come loose, and inspect it periodically. Also ground antenna masts and wind generator towers.

GROUND THE NEGATIVE SIDE OF YOUR POWER SYSTEM, but FIRST make the following test for leakage to ground: Obtain a common "multi-tester". Set it on the highest "milliamp" scale. Place the negative probe on battery neg. and the positive probe on your ground system. No reading? Good. Now switch it down to the lowest milli- or microamp scale and try again. If you get only a few microamps, or zero, THEN GROUND YOUR BATTERY NEGATIVE. If you DID read leakage to ground, check your system for something on the positive side that may be contacting earth somehow. (If you read a few microamps to ground, it is probably your meter detecting radio station signals.)

Connect your DC negative to ground ONLY IN ONE PLACE, at a negative battery connection or other main negative junction nearby (at a disconnect switch or inverter, for instance. Do NOT ground negative at the array or at any other points.