Grounding off grid system

yrtrncyrtrnc Solar Expert Posts: 43 ✭✭

Hi

System is victron quattro 10000 va inverter, 150 /70 mppt victron cc and 12 victron 100 Ah 12.8 V lifepo4 batteries wired as 51.2v 300 ah bank.


Should I ground battery minus, cc chassis and inverter chassis seperately with own ground rod or should I wire to ground bus bar in main consumer unit?


Also, solar system room is metallic. Should I bond to common earth or bond to seperate earth with battery minus, cc and inverter chassis.? If I bond battery minus and solar room would it be dangerous to accidentally touch battery positive while touching mettalic room?


Main consumer unit is 60 meters away from solar room and panels. Inverter is connected to consumer unit via 60 meter long 2 core 16mm cables and 10mm earth wire.


Regards

Comments

  • yrtrncyrtrnc Solar Expert Posts: 43 ✭✭

    Solar panels mounted on metallic solar room.

  • wellbuiltwellbuilt Solar Expert Posts: 415 ✭✭✭

    I’m no expert , but in my system all grounds lead to a common ground rod next to my utility room which is attached to my garage .

    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
  • EstragonEstragon Registered Users Posts: 4,177 ✭✭✭✭✭
    edited February 23 #4

    I have my pv frames grounded to a separate plate near the arrays, but they're up high on a non-conductive structure.

    In the pic, it looks like frames and conductive structure is close to ground though, so I'd ground them back to the main grounding point.

    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • jonrjonr Solar Expert Posts: 1,326 ✭✭✭✭

    IMO, it's best to bond everything together and run it to a single ground point. If over 30 feet or so, bury bare copper wire in the ground to bond the two locations.

    I am available for custom hardware/firmware development

  • yrtrncyrtrnc Solar Expert Posts: 43 ✭✭

    So bond the battery negative terminal the inverter ground and inverter chassis ground the cc chassis grojnd and solar panels and run a 60m bare wire to the main ac panel and connect to earth?

  • jonrjonr Solar Expert Posts: 1,326 ✭✭✭✭
    edited February 24 #7

    I'd also check with a local expert that knows code. And manufacturer instructions. Try a wire with a small fuse first.

    I am available for custom hardware/firmware development

  • softdownsoftdown Solar Expert Posts: 2,690 ✭✭✭✭

    Grounding solar equipment seems a bit unique. From the information gleaned here and there, I employed four grounds and three separate grounding rods. Dry soil is more difficult to achieve a good ground in by the way.

    I used three grounding rods for my electric fence after finding an electric fence grounding kit that contained three rods. This soil is often very dry - this is a desert,

    The solar array that uses a forklift battery only has one proper ground at this moment in time - on battery negative. I should work on that along with 100 other things. Jammed so many wires through the hole in concrete that no more wires will go through.

    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • BB.BB. Super Moderators, Administrators Posts: 29,701 admin

    There are several major reasons for grounding.

    The first, is to provide a return path to the power source so that if there is a short circuit somewhere, you want to pop the fuse/circuit breaker at the source of the power.

    For example, say your 60 meter distant power load is mounted to a metal structure (metal electrical box, metal building, or metal structure. If you get a Hot to metal structure short circuit, there is not enough current flow back through the earth back to your main panel, so the structure becomes "hot" and if, for example, you get some rain and wet ground/grass, somebody touching the metal structure and wet feet, gets electrocuted.

    To prevent this from happening. You have a ground rod at the outside edge of your power shed (outside edge to prevent bringing lightning into the middle of the building--Lightning, discussed next). You run your battery negative to the ground rod, and the case of any electrical devices (electrical boxes, chassis of AC inverter etc.) to the ground rod. Also, if your AC inverter is a pure/true sine wave inverter, it is common to ground the Neutral Connection to your green wire ground bus bar (electrical conduit, etc.). And the green wire from your electrical panel goes to the ground rod too. That way, if there is any short circuit in your building wiring, it goes to the ground rod then back to the power source (neutral/ground bonding) to trip the breaker.

    For the remote load site, you drive another ground rod (outside exterior wall if present), and ground all of the metal framework/electrical boxes/etc. to the ground rod. And you run (ideally, a minimum 6 AWG wire from the main building to the load--60 meters--Local ground rod connected to remote ground rod. This provides the current path to safely short out the AC power source and trip the breaker (and reduce the chance for electrocution.

    The reason for the ground rod is (mostly) for lighting protection. You want metail ("air terminals" or lightning rods) to have a short, direct (no sharp bends) to the "local ground rod" (lightning will "jump" square bends and find another path to ground). This is true at the remote load site, as well as at the main building/power shed. You want the lightning to go to earth, rather than into your system.

    Note: MSW (Modified Sine/Square Wave) AC inverters--You (generally) cannot ground reference the Neutral connection to a common ground--It creates a short circuit through the inverter back to the DC Battery Bank, through the battery negative to common ground rod.

    There are other reasons to ground bond your AC neutral--Some fluorescent lamps need greenwire to earth bonding to start reliably, and some electric stove/water heater ignition systems need the grounding to work correctly (flame detect circuit).

    System grounding can be a very complex subject. Ask questions and do research. Surge suppressors are very nice to have (DC and AC sides of your system) if you live in a lightning prone area. And nothing will prevent damage if you have a direct or nearby strike.

    Some links to read:

    Re: Working Thread for Solar Beginner Post/FAQ

    A couple threads about Lightning:

    Off Grid Grounding Technique?

    Another Question, this time about Lightning

    Note, the above are discussions, not a do A, B, and C--and you will be "safe". There probably is no such thing with lightning. Several different techniques are discussed--and a few of those posters even have experience with lightning. :cool:

    And our host's FAQ:

    Lightning Protection for PV Systems

    From other past posts here, Windsun (admin/owner of NAWS), he said that most of lighting induced failures he saw were in the Inverters' AC output section.

    Towards the end of this thread is a very nice discussion of proper generator grounding.

    If you are in a lightning prone area, There is a whole bunch of details that can be addressed to make your home & business safer.

    -Bill

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