Grounding Confusion

Hi Everybody, and thanks ahead of time for the kind advice.

I  building a large, trailer-mounted solar generator.  I have built a smaller one already, but want to go larger for an off-grid construction project I am planning.  I am using a 12kw slit phase inverter/charger to supply enough power for a welder or any other higher-amperage/voltage needs I may have while on the construction site.  I am not an electrician, and though I think I mostly understand what I am doing, I get easily confused when it comes to grounding.  I do no want to destroy myself or my equipment.  Here are the facts:

The Inverter is also a generator that requires 240v input for charging. I would like to use it for floating batteries when not using PV. The inverter also has a 2-wire gas generator auto start feature and it might be nice to use that feature sometime also.

PV is supplied by six, 260 watt modules in series/parallel to an Outback FlexMax 60 MPPT charge controller.  The series/parallel wiring connects in a combiner box with a 10000v lightning/surge protector.  The combiner includes a heavy ground wire and bus for the surge protector and panels.  I would prefer to use the rack system as chassis ground.

I will install a 100 amp load center that supplies a 50A/240v welding circuit, a 20A/240v circuit and 4 - 15A/120v Circuits. To have these all GFCI circuits would be great, if possible, since this generator will supply equipment outdoors.

The trailer enclosure, all equipment and racking will be mounted to a very heavy trailer chassis made from thick channel iron - all steel (a former welder's trailer).  PV Modules will be mounted to the side by a panel rack system - steel and aluminum.

Questions:

1. The inverter has both an output neutral and a chassis ground lug:  Where should each of these be sent to? 
2. How to ground the panels: To trailer frame via racking or trailer frame though combiner ground buss; with ground rod 
    electrode when parked; or all of the above?
3. Grounding of the 48 volt battery bank:  Trailer frame or ground rod electrode when parked, or both?
4. Grounding of the charge controller ground lug: Trailer frame or ground rod electrode when parked, or both?
5. Now about the GFCI circuitry:  Grounding in load center buss to where?  Trailer frame or ground electrode when parked, or both?

Again, thanks.

Comments

  • mike95490mike95490 Posts: 7,873Solar Expert ✭✭✭✭
    Beware of welding off of a battery powered inverter.   A welder has a wildly varying input current which can easily confuse and cook a lesser inverter.   You didn't mention what inverter model you are getting 12KW is going to have a lot of overhead consumption. Top end offerings should work OK.

    Alternative - get a engine powered Welder that also has 120/240 output that can connect to the inverter for battery charging ?

    If this will be for some commercial job site, your gear will have to meet OHSA safety regs, and that likely involves GFIC outlets
    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 ,

  • SolarNubeSolarNube Posts: 8Registered Users ✭✭
    This is a top end, pure sine wave inverter with 90% efficiency.
  • VicVic Posts: 2,904Solar Expert ✭✭✭✭

    Agree with Mike,   I would NEVER even think of running  any 50/50 Hz transformer type welder from any on the inverter chargers here.

    And,   it is not clear about the maximum power demands of the welder,   but you might well need a large,   heavy battery bank to feed a larger welder.

    Inverter-welders might not put as much stress on the inverter,   as would a low-frequency transformer type welder ...

    Engine-driven welders from name-brand suppliers ARE quite robust,  portable,   and often can supply 120/240 VAC at reasonable power levels,   as well.

    Just sayin',   FWIW,   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.
  • SolarNubeSolarNube Posts: 8Registered Users ✭✭
    I plant use a small welder - I do no expect to weld anything above 3/16 thick, so I can get away with a single phase welder that yanks about 30A at a crack, max.  I think I'll be fine.

    Can anyone comment on my grounding questions?
  • bill von novakbill von novak Posts: 772Solar Expert ✭✭✭✭
    edited June 15 #6

    1. The inverter has both an output neutral and a chassis ground lug:  Where should each of these be sent to? 
    2. How to ground the panels: To trailer frame via racking or trailer frame though combiner ground buss; with ground rod 
        electrode when parked; or all of the above?
    3. Grounding of the 48 volt battery bank:  Trailer frame or ground rod electrode when parked, or both?
    4. Grounding of the charge controller ground lug: Trailer frame or ground rod electrode when parked, or both?
    5. Now about the GFCI circuitry:  Grounding in load center buss to where?  Trailer frame or ground electrode when parked, or both?

    Again, thanks.
    If the load center will be on the ground rather than the trailer (a good idea BTW) then it's pretty straightforward.  Panel is grounded to an appropriate ground (type of soil vs. local code for residential systems will be a good guide here.)  That's the one point where neutral and ground are commoned. Everything else ties into the panel.  In cases where the source or load has separate grounds and neutrals, they all get run back to the panel before being commoned.

    For the panels I would ground them separately for lightning protection.

    For the batteries go with your inverter install manual for the recommendation.  Negative ground or floating are the two most common arrangements.

    For GFCI, ground in load center.
  • SolarNubeSolarNube Posts: 8Registered Users ✭✭
    Thank you Bill.  The load center will actually be attached to the trailer, but I can connect a ground rod electrode directly to load center panel and naturally ground it wherever I am working. Since the load center panel is installed in the trailer and is common with neutral, my thinking is that I should not ground it to the trailer frame with everything else, and I believe you have confirmed that.

    The inverter manual does not specify grounding for the battery bank. Since it is in a moving vehicle that can jostle things around it seems to me that at least grounding it to the trailer frame would be a good idea. Do you see any problem with this  Thanks!
  • mcgivormcgivor Posts: 2,164Solar Expert ✭✭✭✭✭
    The whole grounding issue with regards to mobile applications is open to interpretation, since there should be only one neutral bonding point, a mobile system which is connected to grid via a shore power connection would rely on the neutral bonding of the source. When there is no external neutral bonding, as in a solar application independent of grid power, then a new neutral bonding point  should be established in the form of a ground rod or other suitable means, this would be regarded as a temporary application, which would allow GFCI devices to function. When a generator is connected, for supplemental input , the neutral bond within the generator, should be disabled  to conform to the single point rule. The chassis bonding to ground would protect devices within the the otherwise isolated mobile platform, Establishment of a temporary neutral bond to ground at the load center would be sufficient, but the word temporary is important, as soon as the system is connected to a grid source the neutral bond transfers to the source, or the grid neutral. Not difficult in concept but rather complicated to put in words.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 

  • SolarNubeSolarNube Posts: 8Registered Users ✭✭
    Complicated when put into words, yes, which is why I asked specifically 'where to hook what' instead.

    So, if I understand you correctly, when I plug the inverter/charger into a 220v shore power source to maintain my batteries or hook up a generator to the inverter (whether or not the inverter is supplying a load) then I SHOULD NOT have a ground rod in the ground, correct?

    And also to confirm:  The trailer frame is sufficient chassis ground for all other items, besides the load center and the PV modules, regardless of power source?


  • mcgivormcgivor Posts: 2,164Solar Expert ✭✭✭✭✭
    If connected to a grid source the neutral bonding is taken care of, presumably, so no additional neutral bonding would be required, only if thr system is isolated from the grid would a neutral bonding be required.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 

  • BB.BB. Posts: 27,785Super Moderators admin
    More or less, for an RV that is not permanently on blocks, and has water plumbing and utility power, the only reason a "ground rod" is useful or helpful is for grounding of static electricity or possibly lightning grounding. Otherwise, there is not much reason for grounding an RV to earth.

    If the RV is wired to utility power, then the connection from the utility plug should include a green wire safety ground--That should be attached to your RV frame for safety grounding (if there is a short circuit from 120/140 VAC hot RV metal, you want to trip the breakers in the RV or Utility Panel).

    The neutral (white wire in North America) to frame ground in an RV is a more complex issue. If you have a floating power system (connection to a transformer or even a car battery with no "neutral/ground bond")... You really should have fuses or circuit breakers on both the "Hot" and "Return" leads. With floating power systems, if there is a short circuit in the "return power lead", it can cause a fire unless there is protection in the return leads (as well as the Hot leads).

    A ground (or frame) referenced system (which North American 120/240 Split Phase Power) is... A short circuit from return (neutral) to frame does not cause current flow (they are both at zero volts because of the neutral/return/frame bonding). So, you only need to put fuses/breakers in the "hot" leads (or + leads for a DC power system).

    You can put multiple Neutral to earth (metal frame) ground connections in your RV (and in the main power panel of the Utility power supply (for example ).

    However you can end up with problems.

    One is that you now have parallel current paths. Current flows both through the normal "neutral" wiring, and through the green wire/frame safety grounds. That is not a good idea (can cause overheating of safety grounds and frame connections and in the metal of the electrical service boxes--Not common problems, but they are possible for complex reasons).

    The other is, say you have a GFI (ground fault interrupter in the US, in Europe called a residual-current device with a circuit breaker). If you have a neutral to earth/green wire bond in the Main Utility Power Panel (or genset), use a GFI or RCD for safety (many times required for code for outdoor and near water/sinks/pools), and another neutral to green wire bond in the RV, then will probably trip the GFI/RCD.

    If you use GFI/RCD for your "final connections" (to branch wiring, GFI in outlets, at RV power receptacle, or similar), then you really do not need a neutral bond inside the trailer. At least in the US, I believe our code accepts GFI Outlets as a substitute for not needing a green wire safety ground.

    Sorry for the word salad. This is a complex subject and serious questions about safety are involved.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SolarNubeSolarNube Posts: 8Registered Users ✭✭
    …..and hence, the confusion...I think I'll just hire an electrician to look at my stuff and advise me on grounding. It's just easier to have him tell me where to 'connect what where, and when' than to get this deep into electrical theory, haha. Thanks everybody.
  • BB.BB. Posts: 27,785Super Moderators admin
    Electricians don't always know the correct answers either.

    Want safe? Don't ground bond the ac panel in the RV.

    Use a plug to connect to the account utility power or to generator. Use gfi or rcd devices for ac outlets.

    Don't bother with ground rods (or ground plates) unless you are camping in a lightning prone area (for weeks or months at a time).

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SolarNubeSolarNube Posts: 8Registered Users ✭✭
    That seems straightforward, Bill. Thanks. This will be a trailer-mounted solar generator with 19,200 watts of battery power, 1560 watts of modules, and a 12kw inverter. So, as I understand you:

    1. Inverter AC output NEUTRAL goes to NEUTRAL BUSS in the load center panel.

    2. The Inverter chassis GROUND LUG goes to load center GROUND BUSS.

    3. Ground the load center panel/ground buss to trailer frame.

    4. DO NOT bond ground to neutral buss in the load center. Never the twain shall meet.

    5. GFCI branch circuitry NEUTRALS go to load center NEUTRAL BUSS.

    6. GFCI branch circuitry GROUND wires go to load center GROUND BUSS.

    7. Ground EVERYTHING ELSE (panel boxes, charge controller chassis, BATTERY BANK, PVs, etc.) to load center GROUND BUSS.

    8. No ground rod electrode, except in case of extended use.

    I will attach to and carry a ground rod for the trailer frame, since I expect to have the solar generator on site for several months, using it. But will disconnect it in case of Grid or gas generator AC Input.

    Does all of this seem right to you? I appreciate your help.



  • BB.BB. Posts: 27,785Super Moderators admin
    Do you have a link to the inverter/charger or Brand/model number?

    I forgot that this was a large portable solar powered+genset powered trailer. You need to look at each and every major component to ensure that you understand how they are designed and how the (manuals) recommend everything be connected.

    It appears, that any AC inverter / Genset / etc. that is over something like 3.5 kWatts is designed and built with it own neutral/ground bonding (in genset panel, in inverter output box, and default connection in many "main AC panels").

    If this is mostly off grid (no utility power), the general design would be to bond the Neutral/Frame/Safety ground in the Main AC panel/breaker box. And make sure that you "lift" the neutral/ground bonds in the Genset and AC inverter.

    HOWEVER, if you have a large AC inverter/charger that is designed for these types of applications many times they have a transfer switch that not only transfers the AC mains, but also the Neturals, and neutral/ground bonding option. (from what little I have seen, any genset or AC inverter over 3kW or so, defaults to neutral/frame ground bonding).

    There are so many ways that these systems can be designed, it is pretty much impossible to give a "generic answer" to these sorts of questions. There is "theory" and there is "truth on the ground".

    Need the details to give accurate and correct answers.

    Regarding electricians, I have seen many that really do not understand high(er) power DC systems (or even larger AC systems like multi horsepower air compressors). They tend to use wiring/cables that are way to small of diameter for the application.

    Having a good schematic on paper first (with all of the major components/wiring/etc. called out) before buying hardware and bolting it together.

    Also, "earth grounding" (ground rod, ground plate, cold water pipes), do not really do anything for 120/240 VAC safety. For example, a "compliant" ground rod has 25 Ohms or less resistance. You can connect 240 VAC to that and get:
    • 240 VAC / 25 Ohms = 9.6 Amps
    That won't even trip a 15 amp circuit breaker. But it is more than enough to electrocute somebody (over 0.02 amps is pretty dangerous if directed through the heart).

    Using GFI breakers (outlets) will typically trip over 0.005 Amps (residential) if there is leakage current from Hot+Neutral (or Hot+Hot) to earth ground. That is what will give your people electrical safety.

    This stuff is not "rocket science"--But you do want to get it right so you have a safe and reliable system in the field.

    There are Ground Fault and Arc Fault breakers--And while they can increase safety--You just don't want to install them everywhere--Only where needed. WIth large power systems, you can have a small amount of leakage current (false GFI trips). And Arc Fault breakers can be easily tripped by universal motors (brushed motors) such as used in many hand tools/drills/saws.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SolarNubeSolarNube Posts: 8Registered Users ✭✭
    Yes, this is  large inverter/charger with an internal transfer switch; and neutral bonding is handled inside the inverter. 

    In the case of AC INPUT to the inverter/charger, it will not accept a neutral, only two hots and a ground.

    So I will not bond ground and neutral anywhere and go as I described above.  In case I die, it was nice chatting with you all.  :-)
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