Small array grounding

KhellSkKhellSk Registered Users Posts: 82 ✭✭
How should I go about grounding these puppies? 

Grounding for leaks and thunder of course. Snow is gone btw
_____________________________________________
[2x Flooded  6v 210ah][12v 30a 400wMax CC]
[5x 48w 15.9Vmp + 1x 100w 17Vmp]


Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,680 admin
    Use metal conduit to route the cables back to the building, metal box with Midnite surge suppressor. 6 AWG cable from metal entry box to ground rod at base of array/wall. 6 AWG from array frames to same ground rod (assuming enters building very close to array). 6 AWG cable from "local ground rod" to main power system ground rod. All bends in 6 AWG something like 12" or greater radius (avoid sharp bends where lightning will jump from cable to elsewhere).

    Something like above?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,575 ✭✭✭✭✭
    BB. said:"... All bends in 6 AWG something like 12" or greater radius (avoid sharp bends where lightning will jump from cable to elsewhere)."
    Thanks Bill, This makes perfect sense, I just had never heard it (read it) I'm sure I have a sharp bend from my array to the grounding rod as it comes down the angle of my array @45degrees to the grounding rod. I'll correct it today.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • bill von novakbill von novak Solar Expert Posts: 891 ✭✭✭✭
    Are those Arco Trilams?  If so, I haven't seen any of those in 30 years!
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    I got a pair of those ARCOs somewhere.  Tony
  • TecnodaveTecnodave Registered Users Posts: 418 ✭✭✭✭
    edited May 2019 #6
    Arco M-75  or Siemens SM-75.....33 cell "self regulating" panels.....I've got a few of those, mine sat on a high hill top in Arizona desert for 30 years, powering a communications repeater,  burnt brown, cracked cells, they still produce near rated power..45-55 watts ea.   david
    2 Classic 150, 2 Kid, 5 arrays 7.5 kw total  2ea.  2S6P Sharp NE-170/NE-165, 1ea. 12P Sanyo HIT 200,  2ea. 4/6P Sanyo HIT 200, MagnaSine MS4024AE, Exeltech XP-1100,  2 Banks L-16 battery, Rolls-Surette S-530 and Interstate Traction, Shunts with whizbangJr and Bogart Tri-Metric, iCharger i208B  dc-dc buck/boost converter with BMS for small form lithium 8S 16650 or LiFePO4,
  • KhellSkKhellSk Registered Users Posts: 82 ✭✭
    BB. said:
    Use metal conduit to route the cables back to the building, metal box with Midnite surge suppressor. 6 AWG cable from metal entry box to ground rod at base of array/wall. 6 AWG from array frames to same ground rod (assuming enters building very close to array). 6 AWG cable from "local ground rod" to main power system ground rod. All bends in 6 AWG something like 12" or greater radius (avoid sharp bends where lightning will jump from cable to elsewhere).

    Something like above?

    -Bill
    Doesnt make sense to me could you speak plainly please. 

    You want me to use 2 rods ? Local and system. Why ? Everything is withtin a 12ft radius...

    1. Pretty sure 6awg is over doing it. Im down to bring out a thick wire from inside to a rod outside, linking frames to one another then to the one rod. But from both panel or from inside instalation that would need a 18ft lenght of wire to get to the rod MAX. Forget laws, Wouldnt a an 8awg be more than enough for this application?

    2. Also about conduit I know using metal conduit protect from mechanical damages and makes a second ground but wouldnt pvc.conduit be enough. Emt is expensive. Also, wouldnt using conduit outside make condensation inside the tube ?

    3. About the rod or grounding plate. Inside of buying a copper one couldnt I use a thick aluminum tube, say 2 or 3 inch wide?

    _____________________________________________
    [2x Flooded  6v 210ah][12v 30a 400wMax CC]
    [5x 48w 15.9Vmp + 1x 100w 17Vmp]


  • BB.BB. Super Moderators, Administrators Posts: 31,680 admin
    The "Lightning" ground rod should be on the outside of the building next to the wall (and/or directly under the array).

    IF you already have a building/system ground rod that meets that (close by and exterior to building wall/foundation) then using a single rod for lightning ground and "system ground" is fine (as long as it is within ~10-20 feet maximum horizontal distance from base of array).

    The suggestion to bridge two ground rods with 6 AWG cable is not really for lightning control, but to provide a ground path for DC and 60 Hz short circuit current... I.e., if there is a short from +/- to frame, or a 120 VAC circuit to frame, the 6 AWG provides a ground path back to the main panel and will trip a circuit breaker. Without a 6 AWG between to ground "systems" 10's of feet (or longer) is that a short to ground rod/earth ground is too high of resistance to trip a 15 amp circuit breaker. Tying all ground together, then if there is a short, the 6 AWG is always there to provide a hard return path to the main panel/battery bank/etc. and trip the breaker/fuse.

    The reason is, for something like 6 AWG cable, the impedance of the cable is enough that lightning can leave the cable and find an alternate path to ground much over a ~10 foot run.

    Also, lightning likes to flow to the "edge of the building". If you had (for example) a rooftop array and ran the ground wiring down through the center of the home to a ground rod/plate/cold water pipe... The lightning would try to find horizontal runs (wiring, metal ducting, etc.) to move out sideways to the building boundaries. Lighting is an Alternating Current that acts more like (low frequency) radio energy--And does not "simply" follow the wiring like DC or 60 Hz AC does.

    And, perhaps you missread my 12 INCH radius of bends in 6 AWG lightning ground... Meaning no sharp right angle bends, the impedance (combination of resistance and inductance) increases at right angle bends (inductance increases)--Which can cause the lightning to leave at the right angle bend and find a different path to ground.

    I did not make any 12 foot radius comment that I remember.

    I do not know code in detail, and there are differences between metal and PVC based conduit. Starting with Code and following that is always a good place to begin with. Metal conduit (exterior) always seemed like it was more sun/heat resistant that PVC--But if code allows, I am not going to say anything.

    Metal conduit (especially the first 10 feet grounded back to the AC inverter, etc.) is also a big help to lessen radio emissions (if you are a HAM radio operator or like to listen to AM radio). It acts like a filter and helps ground RF noise.

    Aluminum is always "iffy" as a conductor. Pure aluminum is not a bad conductor itself, but quickly (within minutes) begins to build an insulating oxide layer/skin on it surface. Lighting won't care, but lower voltage DC and AC circuits will see the equivalent of dipping the alumining ground pipe just like it was dipped in insulating plastic.

    Higher alloy Aluminum also forms something called intergranular corrosion in damp/poorly surface treated (anodized/alodine/etc.) structural sections.... Again, won't last long underground.

    Another problem with aluminum is making reliable long term electrical connections. A connection starts to develop an oxide layer on the aluminum... The extra resistance causes the connection to heat. Aluminum expands and extrudes from the electrical joint. After current is turned off, the aluminum cools and contracts from the electrical joint and forms more oxide skin. Repeat over a few years or decades, and you can have a fire (problems with 1970's aluminum wiring in home construction). Normally, you will not have (much) current flow through your ground wiring, but is still an issue. They have worked very hard to make CU/AL rated wiring contacts (i.e., CU/AL rated wall outlets) to try and reduce the high rates of aluminum expansion/contraction vs copper and steel--But it is still a better idea to avoid aluminum in most wiring.

    Aluminum wiring is still heavily used by utilities (and down leads from the pole to your home)--But they use grease filled compression fittings that make very good oxygen free connections, keep water/oxygen out, and hold "crimp" pressure on the CU/AL wiring for decades to come.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • KhellSkKhellSk Registered Users Posts: 82 ✭✭
    edited June 2019 #9
    I will have an fm radio eventualy but understand this;  I have neither a distribution panel nor an inverter. My "panel" is a 6inch pull box that I mounted a boat thing on it, it has 1 12v cig plug, 1 usb 5v 2amp, 1 volt meter and a switch that has a 12v led strip on it. Thats it. So if im gonna ground something its the pull box thats it. As of.right.now i have a piece of wire connect the negs wires of it all to the ground screw in case the box becomes live. It might be stupid but seemed to make sens to me.

    The 12 foot radius was.me.telling.you that.both.my.array and.my pullbox are within 12 ft.of.each other

    So im.gonna buy a copper rod/plate bury it under the array at the corner of the building. Tie all frames to a 6awg and.bring it to the rod without 90degres.angle in it.

    But.im still confused on how and why you are suggesting.me to ground my "panel"/6inchSq box to the rod so that it trips any fuses...

    I have a fuse between array and CC on the positive. Then 1 between CC and the battery on the positive. And then 1 fuse between.the battery and my 6inchsq box on the positive. I dont see how it would blow a fuse to ground the.box alone, with OR without being tied to the negs/battery return wire. Plus im scared that  leaving the pigtail of negs(return) tied to the ground screw of the 6inchbox AND ALSO TYING IT.to.the rod.outside.st.the same.time. pretty.i could waste.the.battery if.lighthening struck.


    Thanks for.the help btw
    _____________________________________________
    [2x Flooded  6v 210ah][12v 30a 400wMax CC]
    [5x 48w 15.9Vmp + 1x 100w 17Vmp]


  • BB.BB. Super Moderators, Administrators Posts: 31,680 admin
    The idea is that if a wire in the box shorts to the box, that there is a current path back to the energy source to ensure the box/conduit/etc. does not become electrified and cause an electrocution.

    You are correct that even a properly breaker/fused solar panel, if the output is shorted, it will not blow any of the inline fuses/breakers--The wiring is "heavy enough" to carry a 100% dead short current without overheating.

    And this is the weakness with solar panels--Since the cannot surge current like a battery (or genset, utility power, etc.), standard fusing/breaker placement does not reduce the chances of fire or electrocution like the standard NEC wiring rules for house wiring does.

    That is why they created the DC Ground Fault system (measure current between system ground and safety ground, and flip a breaker (or turn off a solar charge controller) to add protection against ground/arc faults (I personally have big issues with this type of DCGFI system--But that is another day).

    Another method is to use an Arc Fault detection circuit--Basically a circuit that detect the typical RF Signature from an Arc Fault, and turn off an energy source (like some Midnite Classic MPPT solar charge controllers).

    There is no perfect safety grounding/shutdown solution, and with solar arrays/DC power systems, the typical solutions are even less perfect.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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