PV Array Grounding/System Grounding

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  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: PV Array Grounding/System Grounding

    dlwindsun, marks, bb, and all others interested,
    i believe i may have a partial handle on those being prone to blowouts with lightning emp. it dawned on me looking over a block diagram of a system that was recently shown to me by marks. mark, you may wish to show this to that electrician for his opinion too. anyway, i noticed that besides the + and - going along, there was a third wire listed, the ground wire. it started at the pvs, went through the dc disconnect (plus any combiners and controllers involved), to the inverter(s) where it met up with the ac ground going through the disconnect (the ground staying connected as by law in the disconnects and all other stages)and out to the ac utility ground rod. what i see wrong with this picture is that the ground came into the home from the pvs and such outside. this is not good from a lightning point of view as it not only gives lightning a direct path into the home from the pv's ground, but also is feeding the emp along the ground wire that is paralleling the + and - wires that go to the rest of the equipement inside the home. this induces the energy into the dc wires like a transformer and if the emp is strong enough it will arc directly to the + and - wires from the ground wire. no way should this be going into the home. you might say "but it has to connect that way as it is stipulated by the nec." imo, it does have to be connected, but not the way everybody is bringing it into the home. if the nec is saying it to be a series circuit from the pvs and such from the outside then into and through the other stuff in the home and then out to the ac ground rod that i challenge them to be dead wrong. anybody see anything by the nec as i didn't read it over again yet?
    know that whatever is outside needs to be grounded outside. this means your outside combiners and pvs go straight to a ground rod with as direct a path to the rod as possible without sharp bends outside. your pv ground wire should go to the utility ac ground rod outside, but this may not be close to the utility ac ground rod. that's where multiple rods and underground interconnects come into play. what was described by me in the block diagram is that the ground has been seriesed from the pvs through the house and then to the ac utility ground rod. even if you grounded the pvs and stuff outside to the ac utility ground rod outside, did you leave the ground connection going from the stuff outside seriesed connected to the stuff inside? if you did the danger is still there and what's worse is that it sets up possible other currents due to ground loops as well as a giant antenna like circumstance for picking up the emp possibly worse than if you had no ground connection at all. remember that the ground wire cannot be sent into the home from items outside the home. that's inviting the trouble. the ground is supposed to be a single ground point of low resistance and that can be accomplished through my many descriptions on using multiple ground rods and interconnecting them if it's not possible to use just the 1 utility ground rod. my way is better and is a paralleled arrangement to a single ground point(the utility ac ground rod) even if that point was widened with a multi ground rod arrangement. as in the block diagram i saw, the series connection of the ground wire presents a higher resistance in the path to ground and exposes all of the equipement (& people too) inside the home to a higher degree of proneness.
    it is my opinion that if say a combiner box is the last item before going into the house then the ground wire will not and should not continue into the house from it. if the next item after that combiner in the house would be a fused disconnect, then the ground wire is started from that point to the rest of the system ultimately ending up at the ac utility ground rod. as i said before, the ground wire path outside should then go from the combiner to the pvs and rails and then down in its own parallel ground circuit to the ac utility ground rod. if i failed to explain this right so as to make everybody understand me it's because i was up all night. i'll try to summarize what i was saying here by you making a break in that series ground circuit where it would enter the home and giving it its own path to ground via a ground wire outside of the home to the same ac utility ground rod or expanded ground system due to the distances between both ac utility ground location and the pv system ground location. bb, i'd be interested in your particular thoughts on this, but what say any of ye on this?
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: PV Array Grounding/System Grounding

    this is an additional to my previous posting. in reading more closely they say you can ground seperately and when doing so to have a seperate rod for the pvs.
    http://www.sandia.gov/pv/docs/PDF/sforty.pdf
    i think my method still is better overall and know the rods can be interconnected underground. this does make for a much better ground because of the expanded soil area the ground is in contact with. i think i'm going to attempt contact with whiles on this to run this all past him.
  • WindsunWindsun Posts: 1,164Solar Expert ✭✭
    Re: PV Array Grounding/System Grounding

    From what I have seen and talking to people about over the past many years, is that by far the most common problems is on the AC side of inverters.

    I suspect that the main reason for that is that quite often the inverters are located quite some distance from the house, like in a battery shed. This means that the AC line has - in effect - a giant antenna on the AC side that is very good at picking up high voltage spikes and EMP even from strikes that are quite a ways off.
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: PV Array Grounding/System Grounding

    yes, that could very well have caused it. it could still be induced into the wires, but running conduit with it grounded only on one end or maybe buried wires is an option too in that case rather than open wires in the air like romex.
    i did send an email off to whiles. i never got a mailer-demon, but i also did not get a reply.
  • arcandsparkarcandspark Posts: 63Solar Expert ✭✭✭✭
    Re: PV Array Grounding/System Grounding

    Has anyone hear of Static Dissipater. They are alittle larger than a basket ball but its a ball of stainless steel spines like a needle cushion. The spines are about 15 to 18 inches long and make a sphere. It is connected to a ground wire and down to a ground rod. The idea is to dissipate the differential voltage build up between the clouds and the ground. Using many sharp pointed spikes on these balls more easily allows the static energy to be released as a kind of St. Almos Fire. Florida Power and Light has them mounted on just about all their high tension power transmission lines running from north Florida to Key West. I figure Florida having the most lightning than any other state they must be using these static dissipaters instead of the ole single spike lightning rods that use to mounted on all the transmission towers because they work better. I also have been working on ways to help protect my systems from lightning, EMP, Spikes, ect. It is a gray area with no set answers. Just thought I would through in my two cents on the static dissipaters. They are becoming more and more popular with tower installation protection. I found a way to make them easily by using 3/32" stainless steel welding rods, installed into a 4/0 cable lug and crimp it down filled with the welding rods. Bend the rods to form a sphere and use electricians cutters to cut the tips at a 60 degree angle leaving a sharp tip. The ground wire can then be bolted to the cable lug and to the structure you want to protect. The local radio ham clubs are making them for their antenna towers and they seem to be working, no lightning stirkes. arcandspark
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: PV Array Grounding/System Grounding

    that would be a fancy lightning rod david.
    i'm updating here that i'm guessing about 1 and 1/2 weeks ago we had a very bad storm blow in. i was watching it for a moment out of my window and saw to the south that lightning had struck the next block down from me. yes i was blinded momentarilly and when my vision came back i found the electric was out. yes, i saw that wonderfull afterglow that lingers in a close strike and it was about 450 feet away from me tops. now what you need to pay attention to is that the lightning hit below me by about 150 ft lower in elevation. i went to survey the damage and saw what was left of a very large ceramic insulator all over the street and sidewalk. i'm guessing this electric line was over 100,000 volts, but it was better that than me. phew 8-)
  • crewzercrewzer Posts: 1,832Registered Users, Solar Expert ✭✭✭✭
    Re: PV Array Grounding/System Grounding

    A link to Wiles' "Code Corner" articles: http://www.nmsu.edu/~tdi/Photovoltaics/Codes-Stds/codecorner.html

    Wiles articles specific to PV array grounding: http://www.nmsu.edu/~tdi/pdf-resources/CC102.pdf and http://www.nmsu.edu/~tdi/pdf-resources/CC103.pdf

    HTH,
    Jim / crewzer
  • rollandelliottrollandelliott Posts: 755Solar Expert ✭✭
    Re: PV Array Grounding/System Grounding

    Hmm I didn't know the DC grounding rod and the AC grounding rod needed to be connected. I guess that adds $200 to the bill! Bare copper grounding wire is not cheap!
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