Battery Bank Negative Grounding

Count me in as another one lost in the maze of grounding questions around grounding. As a bit of background, I have a pre-wired E-panel with midnite controllers and a magnum 4000W 120V inverter, which charges a 24V forklift battery. This system is used to power my off-grid cabin, fed by 2000W of solar panels on my roof. The e-panel and battery bank is in a detached garage. The benefit of the pre-wired epanel is that the install was very simple - connect the panels and battery bank to the e-panel, and then connect the e-panel to my main AC distribution panel (also in my garage). My question relates to grounding of the negative side of the battery bank. The ground bus bar in my e-panel is connected by bare copper wire to the ground bus bar in my main A/C distribution panel. That ground bus bar in the AC distribution panel is then grounded (via bare copper wire) to the earth ground rod (only point of connection to the ground rod). I'm struggling to see how the negative side of my battery bank is grounded. Below is the link to the wiring diagram for the pre-wired e-panel, which may help clarify the question. In the wiring diagram there appears to be a ground wire from inside the battery bank (not not connected to the battery from what I can tell), that is connected to the ground bus bar in the e-panel. I'm unclear as to what/how it's connected to the battery bank.

http://www.midnitesolar.com/pdfs/MNEMS4024-CL200-REVB-120VAC.pdf

Another thing I'm trying to confirm is whether or not my battery and certain devices running off my A/C distribution panel share a common 0V ground, but I'm unclear if that is the case. I'm clearly no electrician, but had an electrician oversee my original installation years ago.

Any direction/help you all can provide would be greatly appreciated! I posted this same question on the Midnite forum given my use of the e-panel, but figured I may get more relevant advice on this forum.

Comments

  • VicVic Solar Expert Posts: 2,970 ✭✭✭✭
    Re: Battery Bank Negative Grounding

    Hi mjp..,

    Believe that on the MidNite (MN) drawing, that ground from the Gnd buss is shown connecting to a MN metal Battery Enclosure. Many/most of us do not have one of those. So, unless you have a metallic battery box, this cable has nothing to do.

    Personally, I run a large insulated, green ground cable from the DC Neg bussbar to the ground rod. In my system, there is a DC ground buss, and an AC ground buss (probably they are connected together inside the inverters).

    Technically, I believe, that the DC grounding cable to the ground rod needs to be large enough to trip the large DC breaker. In my case the DC breakers are 250 A, and used a #4 AWG ground electrode conductor.

    Since the AC and DC busses are really one in the e-panel, perhaps you would need only ground conductor to the ground rod. But it should probably be sized by NEC Table, based on the largest DC circuit breaker in that e-panel I do not live and die by the NEC Code book, but this has passed my inspections.

    YMMV, consult your own expert. Others will have opinions, and so on, Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • mjp24cohomjp24coho Solar Expert Posts: 104 ✭✭✭
    Re: Battery Bank Negative Grounding

    Vic- as you mentioned, the AC and DC busses are one in the e-panel. I have a 4 awg bare copper wire going from there to the main AC distribution panel ground bus, and from there to the main earth ground rod. Would that accomplish what you are referring to? Also, my other question would then be whether that would make it such that the battery and any devices plugged into receptacles tied to the A/C distribution panel are both "sharing the same common 0V ground?
  • VicVic Solar Expert Posts: 2,970 ✭✭✭✭
    Re: Battery Bank Negative Grounding

    mjp,,.

    In the linked diagram, there appears to be no connection between the battery negative, and the ground buss.

    And, cannot comment on just how, where, and the effect of any present or missing connection between the battery negative and any other part of the system, except for any such connections shown in that linked diagram. It really all depends upon how the inverter is wired/connected inside its case, and also similar for the Classic (I guess) ... sorry.

    AND, what is required, is really up to any Authority Having Jurisdiction that my need to pass judgment on the correctness of the way that your system is wired.

    Sorry, am not a Code Jock, and it is up to any person responsible for inspecting your system (if any).

    Good Luck, Vic, the waffle.
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Bank Negative Grounding

    Code now requires DC GFCI which means battery negative and ground are not directly connected as a matter of course.

    If you do not have/are not using DC GFCI you probably need only run one wire from negative to ground; negative is a 'pass through' on most systems. On those that aren't (some use a negative side shunt in the charge controller), grounding the battery negative is all you need do.
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