Solar array and grounding

Hill_CountryHill_Country Solar Expert Posts: 96 ✭✭
I will soon be installing two pole-mounted solar arrays (two General Specialties UPM6x's) to be located about 125 feet (one way) away from where our off-grid power center will be (i.e. charge controller, inverter, load center, etc.) on the house. I will have a MidNite Solar combiner box on one of the UPM6x pole-mounted arrays.

I've done quite a bit of online research/reading on these forums and I wanted to see if I'm on the right track in terms of wiring and grounding (both equipment grounding and lightning grounding).

Due to the distance between the solar array combiner box and the power center/house (~125 ft. one way), I'm wondering what the best way is to properly ground this arrangement for both equipment grounding AND lightning grounding. Since I'm a newbie at this, I'm open to advice. I've got two general questions, labeled below...

Question #1: Lightning Ground
I'm thinking that it is best to have a ground rod located right near the foundation to one of the two UPM6x pole mounts. I would then connect a continuous #6 AWG bare copper wire between both UPM6x's to the ground rod, then to the Ufer ground (bottom footing rebar encased in concrete over 20ft. in length) at the house 125 feet away via that continuous #6 AWG bare copper wire. So, in effect, there is a #6 AWG bare copper wire that runs from one UPM6x to the other UPM6x and into the Combiner box, then underground to the main system ufer ground at the house. Does this #6 AWG bare copper wire need to be run in conduit between the two UPM6x's (pole mounts) and in conduit between the ground rod and the ufer ground at the house? Or should it be direct buried with no conduit? If conduit is suggested, can it be the flexible, non-metallic type conduit?

Question #2: Equipment Ground and Wiring
Regarding the wiring that goes between the combiner box and the house power center (i.e. charge controller, inverter, load panel, etc.), this would consist of a single positive wire, a single negative wire, and a insulated ground wire? All this wiring (THHN #6 AWG) will most likely be put inside flexible, non-metallic conduit and will be buried.

Thank you for your assistance! This forum has given me such a great head-start on this so far!!
100% Off-grid with: 8 Solarworld 275 Watt Panels, 8 Concorde SunXtender 405aH 6v AGM Batteries, MS-4448PAE 48v Inverter, MidNite Solar Classic 200 Charge Controller, 10,000 gallon rainwater collection system, etc.
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Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    Re: Solar array and grounding

    Welcome to the forum HC.

    Grounding is a complex subject... A mix the practical, the codes, and a bit of myth.
    Due to the distance between the solar array combiner box and the power center/house (~125 ft. one way), I'm wondering what the best way is to properly ground this arrangement for both equipment grounding AND lightning grounding. Since I'm a newbie at this, I'm open to advice. I've got two general questions, labeled below...

    That is a long distance from the array to the battery shed. I have evolved in my thinking and would basically be recommending (assuming you are in a lightning prone area of the country):

    1. Drive a ground rod at the base of the array. No farther than 10 feet from the rod. If your two arrays are further than 10' apart, you should probably put in a second ground rod for the array.

    Following code, run a 6 AWG able from each solar panel grounding point, ground your metal frame work, to the ground rod.

    If you put a combiner box on the array--Put in Surge Suppressors on the DC +/- wiring to earth/box ground. Run a ground wire from the box/surge suppressors to the ground rod. Do not ground either the + or - leads from the solar array.

    Do this for both arrays.

    Run a 6 awg cable between the two ground rods (if you use two ground rods). Use bare #6 AWG wire buried direct in contact with the earth (code probably requires 18" minimum trench depth). More contact between ground wire and earth is good.

    At the house/battery shed. If you are paranoid, install surge suppressors at the metal box where the solar cables enter the shed. Run a ground wire from the box to the local ground rod (outside, near the foundation).

    This ground rod should be the same as the AC grounding (main panel ground, AC neutral bonding--this can get complicated with Utility, AC inverters, Backup Genset, etc.). Run your AC grounds to the main house ground rod.

    Run a 6 awg ground cable from the battery negative bus to the master ground rod outside the house/shed.

    All grounding for lighting shall be soft bends (something like 18" radius?).

    It would be a good idea (in my humble opinion) to run a 6 awg wire from the house/shed master ground rod to the remote ground rod at the array. This ties the grounds together and helps prevent energizing the solar array relative to earth ground (i.e., all metal work should be connected together with 6 awg cable). This is so that a short circuit (AC/DC) to ground will pop a breaker/fuse.

    How to ground the AC neutral with multiple AC power sources--That can require further discussion.
    Question #1: Lightning Ground
    I'm thinking that it is best to have a ground rod located right near the foundation to one of the two UPM6x pole mounts. I would then connect a continuous #6 AWG bare copper wire between both UPM6x's to the ground rod, then to the Ufer ground (bottom footing rebar encased in concrete over 20ft. in length) at the house 125 feet away via that continuous #6 AWG bare copper wire. So, in effect, there is a #6 AWG bare copper wire that runs from one UPM6x to the other UPM6x and into the Combiner box, then underground to the main system ufer ground at the house. Does this #6 AWG bare copper wire need to be run in conduit between the two UPM6x's (pole mounts) and in conduit between the ground rod and the ufer ground at the house? Or should it be direct buried with no conduit? If conduit is suggested, can it be the flexible, non-metallic type conduit?

    I don't see any reason to put the ground wire in conduit. Unless you are in a salt/marshy area.
    Question #2: Equipment Ground and Wiring
    Regarding the wiring that goes between the combiner box and the house power center (i.e. charge controller, inverter, load panel, etc.), this would consist of a single positive wire, a single negative wire, and a insulated ground wire? All this wiring (THHN #6 AWG) will most likely be put inside flexible, non-metallic conduit and will be buried.

    What is the Vmp-array and Imp-array ratings? What type of charge controller and battery bank voltage will you be running?

    Anyway, a start. I don't live in an area where lightning is a problem. For areas where there are good chances of lightning strikes, it generally is good to get it right.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Solar array and grounding

    Welcome to the forum,

    My pole mount array is 100 ft from my equipment... the actual cable length (one way) between combiner and my ePanel is 117 ft.

    Here's what I did:

    --Ground rod at both ends, connected by #6 bare in trench.
    I used stranded, but if I had it to do over I would use solid because it is less likely to corrode.

    --2" PVC conduit for the combiner-controller cable.
    I did NOT put an insulated ground wire inside the conduit. I am not a code expert, but I think the lack of insulated ground wire inside the conduit is a code violation. I think the code is worried that the bare wire in the trench may corrode or be broken.

    --Lightning arrester at the combiner box.
    BB. wrote: »
    It would be a good idea (in my humble opinion) from the house/shed master ground rod to the remote ground rod at the array.

    This sentence is missing something.. but I think he's saying to bond the ground rods.
    BB. wrote: »
    I have evolved in my thinking and would basically be recommending (assuming you are in a lightning prone area of the country):

    Bill, remind me what thinking has evolved... I thought (obviously wrongly) that you were now less concerned about bonding distant ground rods. What about code requirement for insulated ground in the conduit?
    BB. wrote: »
    What is the Vmp-array and Imp-array ratings? What type of charge controller and battery bank voltage will you be running?

    I have the same questions... depending on the answers, #6 might be a bit small for two poles of array and 125 ft distance.

    Also, will your equipment and batteries be inside your house?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Hill_CountryHill_Country Solar Expert Posts: 96 ✭✭
    Re: Solar array and grounding

    Thank you for the prompt and thorough responses BB and vtmaps! You were both very helpful.

    To address your questions...for each pole-mount (UPM6x) array I will be using 4 Solarworld 275 watt panels (Vmpp = 31.0 v, Impp = 8.94 a). That means, for the two UPM6x pole-mounts, I will have a total of 8 Solarworld 275 watt panels for the entire system (i.e. a 2200 watt system total). I am planning on having 4 panels in series, so I will be using a MidNite Solar Classic 200 charge controller on a 48 volt system (battery, inverter, etc.). I used a % voltage drop table to figure out that with 4 of the these 275 watt panels in series I can use a #6 AWG and still stay under the 2% drop over that 125 foot distance. All of our equipment (AGM batteries, MidNite Solar Classic 200, Magnum 4448PAE inverter, Mini-Magnum Panel, main breaker box, etc.) will be mounted on the exterior of the house (it will be covered and out of the weather, but still "outside"). The main Ufer ground will be connected in that location as well.

    From reading so much about grounding, etc., I realize that it is a grey area where you can go multiple routes, yet still be NEC code compatible. I just want to make sure I'm not missing anything huge (like having multiple ground points that could set up a voltage between themselves).

    So, from reading y'all's posts...since my two UPM6x pole mounts will be about 10 ft. apart from each other, I will have a ground rod for the first pole mount, a ground rod for the second pole mount, and then a Ufer ground for the house system. All of these ground rods AND the Ufer system should be tied together by a continuous #6 AWG bare copper wire (solid) that is direct buried in the soil about 18 inches down (I have clay soil). Where my confusion comes in is this: the conduit that goes from the solar panel combiner box (I'll only have one combiner box) to the house charge controller/power center (a distance of 125 feet) should have a single positive solar panel wire, a single negative solar panel wire, and then an insulated ground wire all contained in conduit? I calculated these wires to be #6 AWG as well, to achieve the 2% loss requirement for the distance. Is this correct? In effect I would have a bare #6 AWG copper wire (solid) directly buried in the ground, then, next to it, I would have conduit with three wires in it (solar positive, solar negative, and insulated ground wire), correct?

    Your thoughts?
    100% Off-grid with: 8 Solarworld 275 Watt Panels, 8 Concorde SunXtender 405aH 6v AGM Batteries, MS-4448PAE 48v Inverter, MidNite Solar Classic 200 Charge Controller, 10,000 gallon rainwater collection system, etc.
  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    Re: Solar array and grounding

    Thank you vtMaps. Add missing sentence fragment:
    It would be a good idea (in my humble opinion) to run a 6 awg wire from the house/shed master ground rod to the remote ground rod at the array. This ties the grounds together and helps prevent energizing the solar array relative to earth ground (i.e., all metal work should be connected together with 6 awg cable). This is so that a short circuit (AC/DC) to ground will pop a breaker/fuse.

    My thinking has changed from being very worried about isolating grounds/ground connections to prevent injection of lightning energy into the wiring.

    Now, I believe that it is better to tie ground rods/grounding in multiple locations to things like bonded AC neutrals. And tying distant ground rods together with a bonding wire (like the 100' foot from array to main battery shed/home).

    I believe it is better to put the energy into the ground and that connecting remote ground rods together helps prevent energizing remote structures with DC or AC power in the event of a short. Ground connections can be as high as ~25 ohms from structure to ground. That is very easy for a short circuit (say from an AC line from AC mains/inverter to metal structure at the array (AC outlet/yard light installed at array--for example). If there is a ground wire from the array frame to the master ground rod at the house--There is now a 6 AWG cable that can carry enough current to pop the AC breaker back at the main panel.

    This "copies" the way AC power is distributed by the utility. AC neutral bonded to ground rod at the pole transformer. And another AC Neutral to ground rod bonded at each home connected to the transformer (2-5+ homes?). Kinds of blows the only bond Neutral to Earth in one location that we normally give as advice.

    Regarding wire gauge from array to house, if these are the correct panels:

    Voc: 39.4 Volts
    Vmp: 31.0 Volts
    Isc: 9.58 Amps
    Imp: 8.94 Amps

    Then you will have ~18 amps over 125 feet + say 15 feet for run down from array and into the home/shed = 140 feet total.

    Using a generic voltage drop calculator and a maximum of 3% voltage drop (0.03*31v*4 panels in series=3.7votls):

    8 awg -> 3.8 volt drop
    6 awg -> 2.4 volt drop
    4 awg -> 1.5 volt drop

    So, 6 AWG cable from array to battery shed/home MPPT charge controller would be a good size.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Hill_CountryHill_Country Solar Expert Posts: 96 ✭✭
    Re: Solar array and grounding

    Thanks for your help! It helps to have someone with your experience help to verify things.

    So, getting at the meat of my question...with the current dual pole-mount arrays (two UPM6x array mounts, spaced about 10ft. apart, with one combiner box on only one of the UPM6x pole mounts...and the distance from the combiner box to the house/power center being about 125 ft.)...I should do the following:

    1) A single #6 AWG bare copper wire (solid) connected from one of the pole-mounts (the one without the combiner box) to a ground rod placed close by, then connected, via direct burial (no conduit!) a distance through about 10 ft. of soil at 18inch depth to the other UPM6x pole mount (the one pole mount with the Combiner box) to another ground rod, then, via direct burial at 18inches depth (again, direct burial, no conduit), about 125 ft. to the main system ground (Ufer ground in our house slab footing).

    2) The solar array's positive, negative, and equipment ground wiring will be from the combiner box to the house power center (where the CC, Inverter, Batteries, etc. are located), a distance of about 125 feet, will be #6 AWG THHN wire (stranded or solid) placed in flexible, non-metallic 1 inch diameter conduit buried at 18inches in the soil. The single #6 AWG bare copper wire (solid) that is direct buried will be in the same trench as the conduit.

    Does this sound correct (and safe)?
    100% Off-grid with: 8 Solarworld 275 Watt Panels, 8 Concorde SunXtender 405aH 6v AGM Batteries, MS-4448PAE 48v Inverter, MidNite Solar Classic 200 Charge Controller, 10,000 gallon rainwater collection system, etc.
  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    Re: Solar array and grounding

    I am not addressing the NEC code... That you will have to take care of.

    However, if you have a 125' cut in the ground open... I would highly suggest burying larger diameter conduit for easier pull/more cables later (if you decide to add on more arrays). Also, I personally, would add a big old second conduit (I am cheap, I have used larger diameter black ABS) so you can pull other stuff later (networking/communications lines, legal conduit if you want to run AC to the back 40 acres, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Solar array and grounding

    side chatter here from me
    i guess bill's thoughts were influenced by me. my general take on it is the best possible arrangement would be the burying of the interconnecting wire for tying the ground rods together as i view this as ideal. there's also a general rule of thumb for there to be only 1 ground point. the problem arrises with the nec not knowing some aspects of grounding when lightning is considered. they require a ground wire to be sent with the pv wires making for a 2nd ground connecting path (rule of thumb is only 1 path to ground due to ground loops) as was mentioned energized wires will induce energy to paralleled wires as well. the nec isn't all wise or safe or even experts as they like to portray themselves as in all areas of electric. the ground wire in the conduit is required by nec rules and this is often made to be law by the ahj. you are now more prone to something going awry just because the wire is also tying all of the rods together is present and the required wire in the conduit is paralleling the other wires.

    the nec does not condone or encourage the use of the buried ground wire that tie rods together or they would relinquish the other required ground wire from its existence. the nec is paranoid because they can't see a wire underground. they literally encourage damages by their requirements imo and it's possibly life threatening too. don't get me wrong here as the 2 rods at the pvs should be tied to one another as my concerns here are the 125ft distances to the utility ground.

    so enter the distances involved with your rods from the pvs to the main utility ground and the ground resistance rises with that distance. this diminishes the possibility of high voltages developing from one rod to the other 125ft away just as you see no inter tying of utility poles excepting the overhead ground wire traveling with the hots. all of the aspects that have been addressed with spd use and what have you still holds true and is good advice for sure. the real problem is the needed option to separate the ground lead from the pv leads and bury it or at least allow for it to travel separately with protections if not buried. i advocate the buried bare copper ground wire inter-tie as it extends a grounding system to be a super grounding system which even the nec can't argue is desirable. this also eliminates parallel induction into the other wires and suppresses above ground pick up of lightning emp through that wire. being only 1 path should be used for grounding purposes this eliminates the tie from 125ft away because of those reasons and the creation of ground loops.

    i do hope i'm not confusing people, but often people are forced to employ the nec rules by law eliminating as a possibility the ideal buried ground wire inter tie from those separated by the long distances. at those distances the effects of the induced voltage differentials in the ground due to a higher resistance path between the pv ground and the main utility ground. is more reason one may not need to bury a very long thick bare copper wire in addition to the reason of law. induced lightning emp is still a problem with the close parallel wires though required by the nec.

    vtmaps,
    you are correct that the nec requires a buried wire to be solid until it reaches a certain gauge that their minimum thickness wire would windup being the minimum size for the strands. yes, it is for corrosion reasons and minimally #8 is the lowest allowed for grounds if i recall correctly, but even if i'm wrong on that account as they like to change things you get the idea what it is they are trying to do.
  • brboyerbrboyer Registered Users Posts: 3
    Re: Solar array and grounding

    You guys think a 3/8" copper ground rod is going to be more effective than a 5" steel pipe buried in several feet of concrete in a hole?
  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: Solar array and grounding

    I find all this to be interesting, and as mentioned, likely the topic that will cause the most confusion/disagreements :)

    So I am wondering, in MY case, my array is 125' from my ePanel.
    I have a ground rod and Midnight SPD at the array, and a ground rod and 2 Midnight SPD's (one on the DC and one on the AC) at the epanel; and the AC/Neut & G and DC/N are all bonded to it at the epanel.

    But I do not have a connection between the two ground rods.
    The PV + and - are going back to the epanel underground via (2) #2 AL wires.

    Ironically, I DO have happen to have an unused #4 AL wire already run underground between the array and the epanel (it was part of the 3 conductor wire I got for free but never used that 3rd conductor).

    Since I have it available, and it would only take 5 minutes, should I connect each end of that #4 to the ground rods to connect them together?
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Solar array and grounding
    brboyer wrote: »
    You guys think a 3/8" copper ground rod is going to be more effective than a 5" steel pipe buried in several feet of concrete in a hole?

    Depends on conditions. A 1/2" ground rod that is set 8 ft into the ground may be more effective than a pipe that only goes down 5 ft. It's all about moisture levels in the soil... if your pipe is in a moist location it is probably OK.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    Re: Solar array and grounding

    A steel pipe with rust and is not to code (that I understand/recall--I am not a code expert). 8-10 foot copper clad rod, or there are buried ground plates aprox 2 square fee in size (if it is difficult to drive a rod 10 feet down).

    Tying the two remote grounds together with the AL cable--I would probably recommend it (more ground rod ties, the better)--However, you would probably need to transition from AL to Copper cable (air/water tight crimp) then make the copper to ground rod connection. I don't think you can make a weather proof/reliable AL to copper rod transition directly.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Solar array and grounding
    niel wrote: »
    vtmaps,
    you are correct that the nec requires a buried wire to be solid

    I hope I didn't say that because I don't know it to be true. It would be a good thing if it were true, because I do think solid is preferable (for corrosion reasons).

    --- 5 minutes later ---

    OK, here's NEC 250.62:
    The grounding electrode conductor shall be of copper, aluminum,
    or copper-clad aluminum. The material selected
    shall be resistant to any corrosive condition existing at the
    installation or shall be protected against corrosion. The conductor
    shall be solid or stranded, insulated, covered, or bare.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: Solar array and grounding
    BB. wrote: »
    Tying the two remote grounds together with the AL cable--I would probably recommend it (more ground rod ties, the better)--However, you would probably need to transition from AL to Copper cable (air/water tight crimp) then make the copper to ground rod connection. I don't think you can make a weather proof/reliable AL to copper rod transition directly.
    -Bill

    Hmmm...at the array, could I connect the AL wire directly to the G-Bus in the combiner where the bare ground starts and then ends up 5 feet away are the ground rod? thet would keep it "weather tight". Or does it technically have to be AT the ground rod?

    And at the "house" side, the ground rod is technically out of the weather. It is UNDER my structure (which is about 3' off the ground on piers). So it is really only exposed to air. I suppose water "could" get to it if we had a flood, but...
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    Re: Solar array and grounding

    Aluminum begins to corrode writhin seconds of being exposed to oxygen. This is one reason why aluminum is so difficult to use with electrical connections.

    A connector/crimp connecter designed to mate aluminum cable shod be used.

    I would prefer not to bring a remote ground into the box... Keep lightning away from your power lines.

    But I am not sure it would matter here when going for ac grounding.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Solar array and grounding

    vtmaps,
    ok i stand corrected on that point as i guess i was remembering wrongly. we still agree it will decay faster being small stranded wire.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Solar array and grounding

    as to the 2 rods at the pvs is concerned you could buy bare #6 and just get maybe 12 or 13ft of it along with 2 proper clamps to attach the 2 pv rods with. much easier than playing with a short length of aluminum wire. i can see it being worthwhile if you did lay out the wire for the 125ft run buried in the soil for the interconnecting of the utility ground rod and the pv ground system at 1 rod. if you want to add another adaptation for the al wire to go to both pv rods you could, but it's extra hassle imo and up to you. if you do use the buried wire for ground rod connecting and have already been inspected i would disconnect the ground wire the nec requires to parallel the pvs wires so you don't have dual paths to the utility ground rod. if no inspections there then eliminate that paralleled pv ground wire in the conduit altogether and just go with the buried ground wire interconnecting the 2 rod systems over that 125ft.
  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: Solar array and grounding
    niel wrote: »
    as to the 2 rods at the pvs is concerned you could buy bare #6 and just get maybe 12 or 13ft of it along with 2 proper clamps to attach the 2 pv rods with. much easier than playing with a short length of aluminum wire. i can see it being worthwhile if you did lay out the wire for the 125ft run buried in the soil for the interconnecting of the utility ground rod and the pv ground system at 1 rod. if you want to add another adaptation for the al wire to go to both pv rods you could, but it's extra hassle imo and up to you. if you do use the buried wire for ground rod connecting and have already been inspected i would disconnect the ground wire the nec requires to parallel the pvs wires so you don't have dual paths to the utility ground rod. if no inspections there then eliminate that paralleled pv ground wire in the conduit altogether and just go with the buried ground wire interconnecting the 2 rod systems over that 125ft.

    No inspections here :)
    And just to clarify, there is only one ground rod at the pv and one at the epanel (technically two at the epanel, 8' apart connected with a #4 bare).
    So it sounds like it would be a good thing to connect the pv and epanel ground rod together since I have that AL wire buried anyways.
    Which brings up a good point, should I have a second ground rod at the pv, 8' apart connected together with a #4/#6 as I do at the epanel?
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    Re: Solar array and grounding

    I believe code requires something like 25 Ohms minimum resistance between earth and ground rod. If you have dry/rocky soil, a single ground rod may not meet those requirements.

    How to measure grounding resistance--Perhaps you can get a local electrician to do that for your--Or find out what your building department normally requires.

    There are other ways to make the resistance less--Mixing chemicals in the soil, wetting the soil, etc...

    http://www.sgscorp.com/chemical_grounding_system.html

    Is it worth the work/costs? I have no idea. If you have lightning in the area--Anything you can (reasonably) do to reduce risks... Probably yes (lots of ground rods, surge suppressors from Midnite, etc.).

    Midnite Solar Surge Protection Devices and Accessories

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: Solar array and grounding
    BB. wrote: »
    If you have dry/rocky soil...

    Nope, this is the Florida swamp :) Nothing but wet sand. Dig a hole anywhere and within 2' down you are hitting water.
    BB. wrote: »
    If you have lightning in the area--Anything you can (reasonably) do to reduce risks... Probably yes (lots of ground rods, surge suppressors from Midnite, etc.).

    Yup, Central Florida, Lightning capital of the US...And I have 3 of the Midnight SPD's.
    I guess I will put the other rod in at the PV, can't hurt and I already have an extra one laying around and plenty of #4 bare copper.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • mike95490mike95490 Solar Expert Posts: 9,582 ✭✭✭✭✭
    Re: Solar array and grounding
    brboyer wrote: »
    You guys think a 3/8" copper ground rod is going to be more effective than a 5" steel pipe buried in several feet of concrete in a hole?

    A proper Ufer ground is 20' of welded joints, 1/2" rebar, in a concrete foundation. Gotta be 1/2 iron rebar, because it's high resistance, gotta be 20' long to provide enough surface area to conduct properly, and it's generally tied to the rest of the steel in the foundation.

    Otherwise, it IS a rusty pipe in a concrete insulating tube.

    Do not embed copper wire into concrete, the chemistry is all wrong, and you will end up with a copper wire that stops at the blue stain in the concrete.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Hill_CountryHill_Country Solar Expert Posts: 96 ✭✭
    Re: Solar array and grounding

    After reading through the various posts I've decided to do the following in terms of wiring/conduit between the two pole-mount solar arrays (which are about 10 ft. apart from each other) and my house (which is about 125ft away from the two pole mounted arrays):

    1) Use 3 #6 AWG THHN/THWN stranded wires (1 positive, 1 negative, and 1 ground) contained in a flexible, non-metallic conduit (1 inch diameter) that is buried about 18 inches underground and that goes between the solar array combiner box (only one combiner box for the two pole-mounts!) and the house, which is about 125ft. in length.

    2) Use a single, bare #6 AWG solid copper ground wire that is attached from one pole-mount solar array down to a ground rod driven into the ground in the immediate vicinity, continuing on underground (direct-burial at 18 inches) about 10 ft. to the other solar-array's ground rod; the same continuous, bare #6 AWG solid copper ground wire is then direct-buried along with the flexible, non-metallic conduit mentioned in item #1 above for about 125ft. to the house.

    3) The main system ground for the entire system is a Ufer ground that is part of the house's reinforced concrete footing (footing is at least 20ft. long, and is tied together via reinforcement steel to other parts of the slab).

    By tying all the grounding rods together (two ground rods total) and having the bare #6 AWG solid copper ground wire direct buried in the earth, as well as being tied to the Ufer ground, I feel that this gives me the best chance at avoid damage. I realize this is a very debatable topic (grounding, especially lightning), but I feel like this will give me a great start.

    If you have any additional thoughts or suggestions, please let me know. This forum has been a valuable resource as I plan my system (nothing has been installed yet!). Thanks!
    100% Off-grid with: 8 Solarworld 275 Watt Panels, 8 Concorde SunXtender 405aH 6v AGM Batteries, MS-4448PAE 48v Inverter, MidNite Solar Classic 200 Charge Controller, 10,000 gallon rainwater collection system, etc.
  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    Re: Solar array and grounding

    For the cable runs--I would again suggest that you use large diameter (possibly non-flexible with large radius turns--Glued together) to allow you to pull new/more cable later. Even adding a second empty conduit/large diameter ABS or similar cheap pipe (I am cheap) for anything else you want to add later (such as an outbuilding/AC power outlet along the 125 foot run--No reason to cut another trench for upgrades later.

    Unless you have access to a "free trencher" and easy to trench soil.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Hill_CountryHill_Country Solar Expert Posts: 96 ✭✭
    As an update, I ended up putting an 8ft. copper-clad ground rod at each array (two total arrays), as well as an 8ft. copper clad ground rod near the power center (inverter/charge controller/etc.). All of the ground rods are tied together by a direct-burial #6 AWG bare copper wire. I used 1.5 inch diameter PVC conduit to connect the array with the power center. In this PVC conduit I put #6 AWG THHN/THWN-2 wiring (positive/negative/ground). I made sure that there is only a single neutral to ground bond for AC and DC in this system (occurs within the MMP). Thanks for all your help y'all!
    100% Off-grid with: 8 Solarworld 275 Watt Panels, 8 Concorde SunXtender 405aH 6v AGM Batteries, MS-4448PAE 48v Inverter, MidNite Solar Classic 200 Charge Controller, 10,000 gallon rainwater collection system, etc.
  • wood4Yodawood4Yoda Registered Users Posts: 6 ✭✭

    So I read through this whole thread because I want to understand how to properly wire up what I am doing.  Maybe not to code so much as I won't be getting it inspected, but so that it functions right.

    Hill country's situation sounds similar to mine with the following exceptions; I am only doing one array right now 740w 4)ET185 panels at 45.03Voc.  I was going to tie them all together so I would have a Voc of about 180 at 5.5 Isc.  I would like to add a second string of something close to those panels in the future, but it won't be the exact as I can't find those panels any longer.  But for calculations (if I am thinking right) I would still be at 180ish, but more like 12amps down the road.  I used a easy VD calc and came up using #6 copper.  My distance is another difference.  I am at 450ish feet, not 125.

    Another difference is I have a 3phase AC wind turbine going up in about the same location on a tilt up tower.  It is a Home Brew turbine wound for 48volts about 1200w.  I ran calcs on wire for this, and came up using #1 AL wire.  From what I understand from people in the Home Brew community we can allow more VD with these turbines because most of the higher VD losses will be in the higher wind range which is rare, and when it does happen you have enough power anyway going into batteries. 

    So my primary question is to understand grounding and bonding.  A bond wire is obviously a good and proper thing.  Problem I might have is I put the cart in front of the horse :) and have conduit buried already 18in down, and didn't lay in a bare copper ground wire.  So now what?  I have a 2in and 1in pvc buried.  Another problem is I didn't put wire in as I was assembling the conduit.  I read this was illegal to do.  Glue getting on wire coating maybe?  I also didn't put a pull chord in as I laid the conduit :/.  Don't this have stupid rookie written all over it?  Hopefully I can shop vac in a small diameter string, and then a pull chord, and then use lots of lube.

    For grounding, what should I be doing?  My tilt up tower has 5 tiers of guide cables (120ft tower), at 4 locations.  I was going to drive a ground rod at each local, and tie each of the 5 cables together to that rod.  Should I then be grounding those 4 rods together with one that I was also going to drive in at the center pivot of the tower?  Should all that be bonded to a wire to the ground rod for the array, and then a bonding wire taken 450ft to the house AC main ground rod?  I still have not been able to find where I can download NEC 690 and 694 on solar and wind to learn some of this.

    So with the absence of a buried bare conductor in my trench what should me bonding wire consist of?  If I read correctly above in vtmaps post you can't run a bonding wire with "hot" wires because you will end up causing some electrical problems along the lines of induction?  Not claiming to get that :) but how does that work then in household wire where whether it is 2 or 3 wire you have hots and bare ground fault wire in the same insulative jacket just separated with some paper?

    So to summarize some; I have a 2in and 1in PVC conduit already in trench covered with no bare wire along side. 

    I am 450ft from my sources to my house where CC, inverter, rectifier, batteries, etc are to go.  (I'm in a cold climate so I don't want to invert at the source)

    I would like some advice on grounding and bonding as well as how to get wire into my long conduit run.

    I am a DIY guy but obviously not the brightest one :)  Go ahead and "trash" me :)  Please just give me whatever help you can in the process!

    David

    PS Thanks in advance.  I really like this forum so far.  I am finding it more helpful, and less critical then some of the others out there. 

  • wood4Yodawood4Yoda Registered Users Posts: 6 ✭✭
    Wanted to add, or also ask there really isn't anything wrong with going with more than a 2 or 3% VD on your solar as long as you end up with enough at the end for charging?  I realize your panel efficiency goes down.  I am more concerned with VD in my wind portion.  Have to factor in 4% in think also in the rectifier.  Losses in the lower voltage wind in my mind means the wind has to blow that much harder to produce more to overcome those losses, but then there is resistance and proper furling to consider.
  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    You are correct... The voltage drop from array/turbine to charge controller (especially MPPT) is much less of an issue than controller to battery bank (or Vmp~17.5 volt array to 12 volt battery bank).

    As long as you have enough working voltage from array/turbine to charge controller--You are fine... Just loss of power and wire heating...

    Obviously, dumping 50 Watts into 100 feet of cable vs dropping 50 watts into 1 foot of cable is different. You can overheat the short length of cable.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Ethan BrushEthan Brush Solar Expert Posts: 235 ✭✭
    I have some opinions and information to add:

    1.   The NEC is not a lightning protection standard.  It only mentions lightning a few times and its grounding and bonding article (250) was not created around lightning protection.  If you feel you need some sort of lighting protection, refer to a lighting protection standard such as NFPA 780.

    2.  I think most people overthink  and over-worry about lightning.  Lightning damage is very rare.  I am doubtful that many "home brew" lightning protection schemes or methods developed from "logical thinking" are very effective.  Personally I will never do anything beyond NEC grounding and bonding.  Actually my wind turbine and solar is not grounded at all.

    3.  There is big obsession with having a "good ground".  I have never really seen any evidence or studies that indicate that a low impedance ground results in any significant benefit.  My understanding is that lightning is a high frequency event and thus "cares" very little about the actual ground resistance. 

    4.  Regarding one of the original specific questions of this thread,  I see no need to obsess about the grounding electrode systems between  two structures and whether/how to interconnect them.  Generally there will be a grounding electrode system at each structure per NEC (Regarding ground mount PV, there may not be a GES requirement - they have waffled back and forth over the last few code cycles) and the two GES's will be linked together by the EGC run with the supply conductors.  I see no issues and for those who do, let me remind you that just about every structure in the US is set up this way - I must have missed all the reports of chronic problems with this.  I am an electrician of 18 years, licensed in three states, a frequent participant in the best professional code forum.  I am not trying to brag or say I know everything, my point is just that being in the field for quite a while and an active continual learner, I think I am more likely to hear about such issues and their frequency than the average joe.
  • Mountain DonMountain Don Solar Expert Posts: 494 ✭✭✭
    I have some opinions and information to add:

    2.  I think most people overthink  and over-worry about lightning.  Lightning damage is very rare. .........
    It might be rare. However it does happen. When it happens it can be devasting. I have personal experience.  I thought the ground rods, wires, surge suppressors we had was adequate protection, especially because "I was never going to be struck by lightning". Nobody I knew had ever had a strike.  Then boom!  We lost a FM60, all boards in the VFX3524M fried, the inverter generator controller box fried and the list goes on; flat screen TV, A/C, speed controller for DC ceiling mount fan blew apart, the DC breaker just before the charge controller blew apart, one GFCI in the AC side fried, not to mention several occurances where the PVC conduit carrying DC from the distant solar array blew apart at the cemented joints.  As well as all the money spent for replacements and repairs we also nstalled lightning protection with air terminals, lots of buried ground points and more and better suppressors. 

    It would have been easier, less stressful, more convenient and definitely cheaper to do good lightning protection before any PV was installed.  That is my opinion. 

    Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
  • Ethan BrushEthan Brush Solar Expert Posts: 235 ✭✭
    I have some opinions and information to add:

    2.  I think most people overthink  and over-worry about lightning.  Lightning damage is very rare. .........
    It might be rare. However it does happen. When it happens it can be devasting. I have personal experience.  I thought the ground rods, wires, surge suppressors we had was adequate protection, especially because "I was never going to be struck by lightning". Nobody I knew had ever had a strike.  Then boom!  We lost a FM60, all boards in the VFX3524M fried, the inverter generator controller box fried and the list goes on; flat screen TV, A/C, speed controller for DC ceiling mount fan blew apart, the DC breaker just before the charge controller blew apart, one GFCI in the AC side fried, not to mention several occurances where the PVC conduit carrying DC from the distant solar array blew apart at the cemented joints.  As well as all the money spent for replacements and repairs we also nstalled lightning protection with air terminals, lots of buried ground points and more and better suppressors. 

    It would have been easier, less stressful, more convenient and definitely cheaper to do good lightning protection before any PV was installed.  That is my opinion. 

    Fair enough, however I have doubts that "better grounding" would have helped in that situation.  Air terminals maybe, those are part of an actual lightning protection  system.   I do think good lighting surge supressors such as the midnite ones are a good idea.
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    FWIW our local installer agrees with you / is a fan of ungrounded systems. But im not convinced. The people that really deal with lightning are the AM radio transmitter guys, with those tall masts. There are descriptions on the net re the seriously big bucks they spend on their grounding systems, and the difference it makes. Bill will  probably be able to lay his hands on one particualr study that i recall he linked to previously.

    Lightning is geographically dispersed. Ive been guilty of drawing conclusions about things that happen or dont happen here. Its easy to do, but you dont have to have been on this forum long to hear about gear  that goes poof from time to time, esp in florida. Happened here as well once.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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