system grounding questions

73 Posts
Aug 30, 2008 12:27 pm
system grounding questions

talk about a confusing part of setting up an off-grid system correctly..Smiley Please give me some feedback.

12v system with 3 panels (1) 20watt (2) 40watt

question #1
1 ground for the combiner/array. A ground rod that is connected to the combiner "ground" buss bar. Connected to this ground buss bar are the following:
neg from the combined neg bus bar
ground wire from panels

question #2
a 2nd ground for the battery bank as follows:
neg from battery terminal to a "ground" bus bar
ground wire from all "metal" enclosures to same "ground" buss bar. This buss bar is then attached to a 2nd ground rod

question #3
(2) grounding rods connected with buried wire.
Do the rods need to be 6'-0" or more apart

any type of help with this confusing topic would be greatly appreciated.
Aug 31, 2008 12:24 pm
Re: system grounding questions

As you scroll down through the above article, you will see a wiring scheme that shows the EGC (equipment grounding conductor) from the PV array is bonded to Earth but, is not bonded to the negative output of the PV array at the combiner boxes, nor is the EGC bonded to negative at the battery bank.
 However, if you look at the EGC at the vdc input to the inverter it is bonded to the neutral conductor as well as Earth.
As well, the EGC is bonded to the neutral conductor at the main breaker panel, which is also bonded to Earth.

I would like to point out though, that this scheme is dated 2003. The NEC (National Electrical Code) makes changes and is revised every three years. The lastest set of codes starts with this years (2008) new code book.

Reading the article, you will find out that the PV array was going to be installed on the rooftop of the dwelling. If this had been done, there would need to be a GFP (Ground Fault Protection) breaker installed in the PV source circuit as well. For more on this and other code compliant PV system information, go to -
73 Posts
Sep 1, 2008 11:19 am
Re: system grounding questions

Thanks for the links Thomas...things are becoming a bit more clear..slowly....It appears that there are way to many variations out there for grounding techniques.

So far it's totally obvious that I must ground all the metal equipment and module frames as well as the negative combined conductor at the combiner a common ground rod..the most confusing part is the negative conductor at the I run a wire from the negative output off the battery to the same ground rod that is used at the combiner box?? OR Does it go to it's own ground rod and then I "bond" the 2 ground rods with buried copper wire?

NOTE: I am only using DC for power form the battery. NO inverter, No tie to is it's own little system

grounding seems to be the most confusing part of system install for sure

578 Posts
Sep 3, 2008 11:50 am
Re: system grounding questions

truer words have not been spoken.  grounding baffles many, don't feel bad.

here is another link, and for a dc system, you would likely pull from your equipment grounding busbar to you grounding electrode conductor to your grounding electrode (ground rod).  in your small system, that would probably mean after you have grounded the modules and rails with the bare copper into the combiner, you would pull a positive, negative and ground into the dc load center.  there other necessary grounding conductors (controllers, enclosures) would meet on the equipment grounding busbar.  depending on where the modules are (on building or not on building for GFP) you may have to bond the negative and grounding conductors in the gfp, OR have to bond the two busbars with a bonding jumper.

perhaps that is helpful, hopefully i did not make it worse.

altE staff

"Making Renewable Do-able"

Tel: 877.878.4060 x107  or +1.978.562.5858 x107
Fax: 877.242.6718  or +1.978.562.5854
73 Posts
Sep 3, 2008 04:22 pm
Re: system grounding questions

ohhh boy..I'm getting dizzy reading all this..Smiley


a separate ground rod at the combiner...which is grounding the following:

negative combiner bus bar
bare copper wire from module frames
a wire connecting all "metal" enclosures

this takes care of the PV input and the "enclosures"

so totally confused about what to do with the neg off the battery that goes to my DC distribution buss the words of Bill The Cat...Ackk!


73 Posts
Sep 3, 2008 04:39 pm
Re: system grounding questions

I think I got the battery Neg ground figured out..

I'll pull a grounding conductor off of my shunt and run it to the ground buss bar in the combiner...the combiner and shunt are very close to each other as they whole panel is mounted on a wall in the garage. The panels themselves are mounted on the exterior wall of the garage so all the wiring is very close.

This then means I only use one "primary" ground rod...

this make sense?

thanks for all your guidance...

wish AltE had classes in the chicago area..Smiley

578 Posts
Sep 3, 2008 05:10 pm
Re: system grounding questions


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)

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. 

altE staff

"Making Renewable Do-able"

Tel: 877.878.4060 x107  or +1.978.562.5858 x107
Fax: 877.242.6718  or +1.978.562.5854
73 Posts
Sep 3, 2008 05:57 pm
Re: system grounding questions

i'm confused now for sure..fell like i'm way over my ski's with trying to figure out proper grounding...Sad

73 Posts
Sep 4, 2008 04:29 pm
Re: system grounding questions

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:


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.


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.

73 Posts
Sep 6, 2008 09:47 am
Re: system grounding questions

O.K. NOW i think I got it....

since all my electrical boxes are in one place inside the garage, including the combiner and the baby box, I'll use (1) grounding electrode to ground equipment AND the NEG power conductor in the following manner:


the ground buss bar at the Midnight Solar MNPV3 combiner has attached to it the bare copper grounding conductor from the panel frames. Also attached to this ground buss bar will be a wire that connects the metal equipment boxes (baby box)(DC distribution box). Also attached to this ground buss bar will be a wire coming from the NEG side of my DC Power Distribution Box.

The ground buss bar is then attached to a ground rod via a grounding conductor of the same size as the largest wire coming from the Battery to the DC Power Distribution Panel.

look good..?!


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