Question about generator grounding - 2 chassis bonds going to different grounding points

Does a generator having two equipment grounds going to different grounding points create a ground loop? Not seeing any sign of malfunction or anything frying with the generator so I'm thinking its ok. Honda Eu generators have floating neutrals. They do bond the chassis to the ground wire that goes out the generator's plugs, which ultimately goes to the house's AC ground, but the neutral and ground are not bonded.

James at the input of a inspector friend of his (because he's only installed 4 systems before mine and Mesa has no inspections wanted to be sure he was doing it right because other Phoenix valley cities do have inspections) drove a ground rod just outside of the concrete slab that the generator is on and bonded it to the generator's frame. This is likely because the generator is a little over 80 feet away from the main service panel (there is only 10 feet from side of house to property wall so the generator had to go into the back yard to avoid breathing generator fumes). Since the only neutral to ground bond is at the main panel, It would be assumed that having two chassis bonds each going to a different ground point wouldn't cause problems down the road?

Also, there are 2 DC/PV ground rods between the generator's ground rod and the house ground (which I think is a uefer on the foundation footing)
«1

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po

    Larger gensets (roughly over something like 3.5 to 5 kW or larger) are usually going to have neutral bonded to chassis/frame ground from the factor. And the green wire will be connected there too. I assume this is because they assume the genset is going to be the primary source of power with larger gensets.

    You would then have a parallel path for current in both the Neutral and Green Wire ground. That is usually not a good idea. Earth ground should never carry current except in the case of a short circuit.

    Normally, you would look for the Neutral/Chassis bond and lift that. There should only be one Neutral+Earth bond in your home wiring (in the main AC panel).

    And, I would run a 6 awg (or what is ever required by code) between the generator ground rod and the main ground rod (to provide a return path to electrical current flow--You want to trip the breaker(s) rather than energize, for example, the generator frame if there is a hot to frame ground short).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po

    I don't see anything wrong with this. Generac recommends this method for their backup generators. They even have a ground lug on the outside to connect to the local rod.

    I though Generac would have frame bonded to neutral (which I would have to remove), but surprisingly it didn't.
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    NorthGuy wrote: »
    I though Generac would have frame bonded to neutral (which I would have to remove), but surprisingly it didn't.

    No, they don't. No standby generator does unless the switchgear has a switched neutral. And switched neutral is only used on installations over 50 kW on single phase service.

    All three-phase standby generators use switchgear with switched neutral because some three-phase service like wild leg delta, for instance, is actually an ungrounded system and neutral is provided by a grounding transformer (sometimes called a "zigzag transformer"). Unbalanced loads on the legs will backfeed the utility service thru the neutral grounding transformer on a wild leg delta three-phase system. So it must be disconnected when on standby power.

    Rule of thumb on generator neutral-ground bonding:
    If the switchgear switches the neutral from utility to genset, the genset must have a bonded neutral. If the switchgear does not switch the neutral (more common), the genset neutral should remain floating as a return path to the generator's winding center tap only.
    --
    Chris
  • YehoshuaAgapao
    YehoshuaAgapao Solar Expert Posts: 280 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    ChrisOlson wrote: »
    Rule of thumb on generator neutral-ground bonding:
    If the switchgear switches the neutral from utility to genset, the genset must have a bonded neutral. If the switchgear does not switch the neutral (more common), the genset neutral should remain floating as a return path to the generator's winding center tap only.
    --
    Chris

    My generator's neutral is hooked to the neutral bus in the PDP so its neutral is never isolated. The netural bus currently has neturals for generator, main panel, subpanel, and inverter hooked on it, plus a Midnite solar lightning arrestor. The inverter's built-in ATS only switches the hots as the only neutral is on AC-out, going to the PDP's neutral bus.
  • YehoshuaAgapao
    YehoshuaAgapao Solar Expert Posts: 280 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    BB. wrote: »
    Larger gensets (roughly over something like 3.5 to 5 kW or larger) are usually going to have neutral bonded to chassis/frame ground from the factor. And the green wire will be connected there too. I assume this is because they assume the genset is going to be the primary source of power with larger gensets.

    You would then have a parallel path for current in both the Neutral and Green Wire ground. That is usually not a good idea. Earth ground should never carry current except in the case of a short circuit.

    Normally, you would look for the Neutral/Chassis bond and lift that. There should only be one Neutral+Earth bond in your home wiring (in the main AC panel).

    And, I would run a 6 awg (or what is ever required by code) between the generator ground rod and the main ground rod (to provide a return path to electrical current flow--You want to trip the breaker(s) rather than energize, for example, the generator frame if there is a hot to frame ground short).

    -Bill

    Only the EB series (industrial/worksite; all sizes) generators has a built-in GFCI and netural-ground bond. The Eu and all other series (all sizes) generators do not - page 20 of http://powerequipment.honda.com/pdf/Brochures/generator_brochure.pdf

    There are 4 grounds total
    • Generator (rod, #6 wire) - Just an equipment ground bond to the generator chassis (#6)
    • PV (rod, #6 wire) - PV equipment ground (#6)
    • DC (rod, #6 wire) - Equipment grounds for the inverter (#6), charge controllers (#10; james refused to do #6 - wiring compartments to ground terminal hellish), combiner boxes (#6), & DC-carrying junction boxes in-between, built-in negative/ground bond in charge controller #1 (#10; #2-4 have GFCI fuses pulled per Xantrex manual), DC lightning arrestors (#12)
    • House/AC (ufer, #4 wire). - Main panel (#6; ufer is #4), subpanel (#6), equipment ground to AC utility disconnect, Generator receptacle ground (#10; hots & neutral are #6), AC lightning arrestors (#12)

    Should all these grounds all be cross-bonded with each other? I believe only the PV and DC ground rods are bonded together currently. All the DC lighting arrestors (blue LED) are seeing acceptable ground even without a bond to the house ground so I was assuming everything was right, but it might not be. I think James believed the AC/DC isolation extended to grounding also.

    Another question, not sure if the charge controller's built-in ground and GFCI grounds the PV, batteries, or both? I'm thinking both because the MPPT voltage conversion is solid-state and therefor there is no isolation. The manual's wiring diagram show a ground going to the battery box, but it looked like an equipment ground, and since my battery boxes are plastic (double-walled HDPE), there is nothing to bond.
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    Should all these grounds all be cross-bonded with each other?

    They should already be bonded with one another thru the ground wiring in your system. You should never have separate or isolated grounding systems. You should be able to pull any of the ground rods and still have the equipment grounded thru another one. Multiple points going to earth ground is OK. But only run a bonding wire between ground points if one is isolated for some reason.

    Isolated grounding points can have potential between them. That should never exist.
    --
    Chris
  • YehoshuaAgapao
    YehoshuaAgapao Solar Expert Posts: 280 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    ChrisOlson wrote: »
    They should already be bonded with one another thru the ground wiring in your system. You should never have separate or isolated grounding systems. You should be able to pull any of the ground rods and still have the equipment grounded thru another one. Multiple points going to earth ground is OK. But only run a bonding wire between ground points if one is isolated for some reason.

    Isolated grounding points can have potential between them. That should never exist.
    --
    Chris

    So would it be ok to bond the DC and PV grounds (DC & PV are directly bonded) to the house ground by connecting the two ground busses in the PDP?

    The generator has an alternative grounding cross-bond albeit a small one, the #10 that is going from the generator receptacle to the AC ground bar in the PDP, which is bonded to the house ground with #6 (The #10 run is longer than the #6). The built-in equipment frame bond goes to this ground. The #6 going to its own ground rod is drilled into the frame separately.
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    So would it be ok to bond the DC and PV grounds (DC & PV are directly bonded) to the house ground by connecting the two ground busses in the PDP?

    I'm pretty sure you can run as many grounds as you want, all over tarnation, as long as you don't connect them to the system neutral in more than one place.

    Your service entrance ground (AC side) and DC power system grounds should all go to the same place though. You don't want those separate, or potential existing between them. Totally separate grounding systems, each with a ground rod, in theory go to the same place - earth ground. But the ground at your service entrance is considered the main one and any extra ground rods should still be hooked to it either by the the ground wires in the equipment or by bonding them directly together.
    --
    Chris
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    ChrisOlson wrote: »
    I'm pretty sure you can run as many grounds as you want, all over tarnation, as long as you don't connect them to the system neutral in more than one place.

    Nope. Single point ground to avoid ground loops (where power can actually come back up out of the Earth and energize other components rather than dissipate). The multiple N-G bonds is another problem.
    Your service entrance ground (AC side) and DC power system grounds should all go to the same place though. You don't want those separate, or potential existing between them. Totally separate grounding systems, each with a ground rod, in theory go to the same place - earth ground. But the ground at your service entrance is considered the main one and any extra ground rods should still be hooked to it either by the the ground wires in the equipment or by bonding them directly together.
    --
    Chris

    And yet sometimes separate grounding is allowed. For example if the distance between grounding points is great enough to eliminate the possibility mentioned above and connecting the two becomes impractical. This is one of those judgment-call things.

    You never know if it's wrong until it doesn't work. :D
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    You never know if it's wrong until it doesn't work. :D

    Yeah. And you know what the other problem is with grounding? You can get three different engineers all together, plus three inspectors, and get six different opinions on what is the right way to ground it. And I'm not kidding, so no smiley.
    --
    Chris
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    ChrisOlson wrote: »
    Yeah. And you know what the other problem is with grounding? You can get three different engineers all together, plus three inspectors, and get six different opinions on what is the right way to ground it. And I'm not kidding, so no smiley.
    --
    Chris

    I know you're not kidding. You're spot on. Except the number of opinions would probably be more than the number of people rendering them. I'm not kidding either. Proper grounding is one of the most discussed, debated, and argued issues in all of electrical engineering.
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    Proper grounding is one of the most discussed, debated, and argued issues in all of electrical engineering.

    And in parenting. When I was younger I seem to remember being grounded a lot - several times I was told it was permanent. :blush:
    --
    Chris
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    ChrisOlson wrote: »
    And in parenting. When I was younger I seem to remember being grounded a lot - several times I was told it was permanent. :blush:
    --
    Chris

    It was permanent: just you try and defy gravity again, young man! :D

    (This probably explains your interest in airplanes.)
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    (This probably explains your interest in airplanes.)

    Interest is about as far as it goes anymore. I owned several of them when I was younger. Then we built an off-grid home and that pretty much ended anything to do with airplanes. After the off-grid home thing about all we can afford for recreation anymore is a used boat that needs a lot of work. :cry:

    --
    Chris
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    ChrisOlson wrote: »
    Interest is about as far as it goes anymore. I owned several of them when I was younger. Then we built an off-grid home and that pretty much ended anything to do with airplanes. After the off-grid home thing about all we can afford for recreation anymore is a used boat that needs a lot of work. :cry:

    --
    Chris

    That sounds oddly familiar. ;)
  • YehoshuaAgapao
    YehoshuaAgapao Solar Expert Posts: 280 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    ChrisOlson wrote: »
    Yeah. And you know what the other problem is with grounding? You can get three different engineers all together, plus three inspectors, and get six different opinions on what is the right way to ground it. And I'm not kidding, so no smiley.
    --
    Chris

    I think I would agree. The NEC seems ok with multiple grounding points, and actually looks like it requires it when the PV is more then 30 meters away, but it does look like it has all the grounding points cross-bonded when multiple grounding points is used. I guess I shoudl at least run a #6 between the two ground bars in the PDP (super easy).


    And does the Xantrex charge controller bond PV negative to ground, battery negative to ground, or both? I'm thinking PV-only or both. Especially if it does both, should the #10 going to charge controller #1's ground be replaced with something bigger since it is not just an equipment ground? The GFCI fuses are pulled for #2-#4 per Xantrex manual. Would it be wise to connect a #6 between the battery negative bus and the ground bar? If the battery bank is grounded to one of these ground bars, should they still get cross-connected? James meant for the top bar to be AC only (connects to house ground) and the bottom bar to be DC & Equipment ground (connected to DC ground rod which is bonded to PV ground rod) - he believed AC and DC should be kept separated even in grounding, which is why they are currently isolated.

    Maybe I should leave the DC and PV grounds isolated because of that other thread the poster didn't ground his PV at all and had great success in Florida (this is where the 3 engineers/3 inspectors/6 opinons kicks in)?
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    And yet sometimes separate grounding is allowed. For example if the distance between grounding points is great enough to eliminate the possibility mentioned above and connecting the two becomes impractical. This is one of those judgment-call things.

    I disagree here. There are already at least two conductors (hot, neutral) running between the two locations. It is as practical to run a ground wire as it is to run the hot and neutral. There's no good reason to not put in the third conductor which connects the two ground rods.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    vtmaps wrote: »
    I disagree here. There are already at least two conductors (hot, neutral) running between the two locations. It is as practical to run a ground wire as it is to run the hot and neutral. There's no good reason to not put in the third conductor which connects the two ground rods.

    --vtMaps

    Unless you're the one footing the bill to bury 200' of #6 bare copper to connect the array frame/mount ground to the system ground at the house.

    Two things that stop me from drawing up a bunch of basic wiring diagrams:

    1). People will say it is wrong and cite a case that comes up in one of ten thousand installations.
    2). People will think the drawing is the only way to do it for every installation.
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    vtmaps wrote: »
    There's no good reason to not put in the third conductor which connects the two ground rods.

    Cost? Our power bunker is 250m from the house and about 350m from the well pump. Running over 500m of ground wire seemed like an unnecessary expense, so I have separate ground rods at each location. Unless I'm misunderstanding earthing systems (quite likely), it seems that doing it this way is the same as a TT earthing system (https://en.wikipedia.org/wiki/Earthing_system#TT_network) and is in use by a number of countries in their grids.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    I think I would agree. The NEC seems ok with multiple grounding points.

    Well it depends on what you mean by "multiple ground points". Multiple grounding rods (or plates) is okay, providing they are connected as a single point ground. The two terms don't mean the same thing. You can have several grounding rods, but they are supposed to be connected together to form one point at which all ground connections converge before making Earth contact.

    The exception to this is, as mentioned, when long distances exist between the rods.
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    And does the Xantrex charge controller bond PV negative to ground, battery negative to ground, or both?

    It's interesting that you ask that question - I did some re-wiring on my solar arrays and high voltage DC bus over the weekend in preparation for installing my XW-MPPT-60 to take some of the peak load off my Classic 150. And since I'm installing dual controllers for the solar, I went to the RE dealer where I get most of my equipment on Saturday morning and bought 1.5kW more panels so I have enough installed capacity (7.5 kW) to run both controllers at 90% of their rated output capacity (total 130 amps).

    I'm going to put in the additional panels today on the house roof (it's cooler here and cloudy today so I can work on the roof without wrecking the shingles) and get them wired into the combiner.

    Then I have to review the -60-150 manual myself to figure out the grounding and ground fault protection for it when I install it.
    --
    Chris
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    ChrisOlson wrote: »
    Then I have to review the -60-150 manual myself to figure out the grounding and ground fault protection for it when I install it.

    It has a fuse (that you can reach from wiring compartment) that connects battery negative to the ground (for GFP). You may have the same in Classics, so you probably need only one of them.

    Battery negative is most likely connected directly to PV negative (you can check continuity if you haven't installed it yet), but they don't mention anything in the docs.
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    NorthGuy wrote: »
    It has a fuse (that you can reach from wiring compartment) that connects battery negative to the ground (for GFP). You may have the same in Classics, so you probably need only one of them.

    Battery negative is most likely connected directly to PV negative (you can check continuity if you haven't installed it yet), but they don't mention anything in the docs.

    That part about grounding has always been confusing to me. The PV- and B- in the Classic is the same - it's internally connected in the Classic, IIRC. I don't know if that's the same on the -60-150 or not. We have the battery negative bus bar bonded to system ground with a 6 AWG bare copper wire that runs from the negative bus bar to the ground rod (which is actually our well pipes here). I'm pretty sure I had to set a jumper in the Classic 150 for that configuration where the DC system ground is already bonded to the system ground (or earth ground).

    So what you're saying is that I should pull that bonding fuse out of the XW-MPPT-60 being we already have both the PV- and B- bonded to earth ground?

    The other thing is, even though I will have two separate arrays - one on each controller - the PV- from both arrays goes to the same PV- bar in my 600V DC bus (and also from the wind turbines). The PV+ and turbine+ (both high voltage, PV at ~92 Vmp and turbines at 140V) go to separate + bars in the bus that each go to their own controller. AFAIK, all those high voltage DC power sources are all connected to B- in the Classics.
    --
    Chris
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    ChrisOlson wrote: »
    So what you're saying is that I should pull that bonding fuse out of the XW-MPPT-60 being we already have both the PV- and B- bonded to earth ground?

    There's a jumper in XW SCC too, which disables the whole GFP thing. You need to disable it if you already have them bonded. Same as in Classics.
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    NorthGuy wrote: »
    There's a jumper in XW SCC too, which disables the whole GFP thing. You need to disable it if you already have them bonded. Same as in Classics.

    Read above - I made an edit to that post.

    But, still, I have to study the manual for the -60-150 on that to make sure I'm doing it right. I had to read it about six times for the Classics when I installed them to make sure I understood it and did it right, and that was awhile ago. So I'm basically starting over on reviewing the GFP thing because I don't remember it all from when I installed the Classics.
    --
    Chris
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po

    So, your first question is do you believe in a "hard ground" between DC Return (typically negative) and Earth/Chassis/building/water pipe ground or an ~1 amp fuse/breaker between DC Return and Earth Ground.

    The jumper should just configure the charge controller(s) to measure the voltage between Earth Ground and DC Return. If there is over X volts between the two, the charge controller stops charging (or, in the case of a ganged 1 amp/80 amp breaker, the tripping of the 1 amp breaker pops the 80 amp breaker too).

    The 1 amp fuse/breaker is used as a UL Listed detection circuit for current flow between DC Return and Earth. Unfortinatually, the opening of the fuse/breaker leaves the DC Return in an unknown state (typically Vbatt or Vpanel + is now grounded by a short to earth, and the DC Return is offset by battery/solar panel voltage/current with respect to ground). The whole DC GFI was originally conceived and implemented by NEC+UL as a Arc Fault detection/prevention scheme (as I understand the history). I believe that the DC GFI creates far more problems/issues than it solves. More or less, it is like turning a car's electrical system from negative to positive ground is there is a short circuit somewhere (lots of issues from that point on between ground references, lack of fuses/breakers on DC return lines, negative no longer being at "zero volts", etc.).

    Personally, for battery based systems--I believe that DC bonding to earth is the correct grounding method for "best at this time" over all safety. It is identical to what is done in North America by Ground Bonding the AC Neutral to Earth Ground/water pipe/etc..

    If you decide to keep DC Return Earth Bonded, then you just need to configure the charge controllers to ignore the GFP circuitry. Although, it should not matter anyway given that the DC Battery Negative is already bonded to earth and there close to zero current/voltage across the GFP detection circuitry.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    ChrisOlson wrote: »
    The other thing is, even though I will have two separate arrays - one on each controller - the PV- from both arrays goes to the same PV- bar in my 600V DC bus (and also from the wind turbines). The PV+ and turbine+ (both high voltage, PV at ~92 Vmp and turbines at 140V) go to separate + bars in the bus that each go to their own controller. AFAIK, all those high voltage DC power sources are all connected to B- in the Classics.

    In the docs, they say that you need to connect each PV- to its own controller (without commin PV- bus!), and specially warn about not crossing the wires between different controllers (page 2-15). I have no idea why, so I decided to follow this recommenation blindly. There's no inner schematic included, and I didn't look under the cover.
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    NorthGuy wrote: »
    In the docs, they say that you need to connect each PV- to its own controller (without commin PV- bus!), and specially warn about not crossing the wires between different controllers (page 2-15). I have no idea why, so I decided to follow this recommenation blindly. There's no inner schematic included, and I didn't look under the cover.

    You see, that's what I don't understand about it. I'd have to ohm it out again, but I am reasonably sure that the PV- and B- in the Classics are interchangeable - they are the same bus in the Classic. So if you run separate PV- from each power source to each controller, and PV- and B- are really the same in the Classic, then they are all connected together anyway thru the same B- going to every controller And at the same time, all your high voltage DC sources are connected to earth ground because of the B- being bonded to earth.

    So that's why, when I wired up my high voltage bus I just used one bar in it for all the high voltage negatives. I'll ohm out the PV- and B- in the XW controller. But if it's the same like it is in the Classic, I don't see what good it does to run a separate PV- to the controller that is isolated from the other PV- and turbine-.

    Confusing.

    All I know is that at present, I can check with an ohm meter from any panel (AC or AC), or any DC- point in my system to earth ground, and there is continuity.
    --
    Chris
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    ChrisOlson wrote: »
    So I'm basically starting over on reviewing the GFP thing because I don't remember it all from when I installed the Classics.

    Well, BB. beat me to it. If you bond your battery neg to ground you defeat all the GFPs.

    Of greater interest is what if you do want GFP? When you have multiple GFPs the fault current (that is supposed to trip the GFP) is divided among the GFPs and may be larger than you would like before it manages to trip them.

    I believe that midnite has some sort of follow-me devised for their GFPs so that only one GFP is used and the other classics get their cue from the one GFP. I don't see how to achieve this with internal GFPs of midnite and xantrex together.

    Outbacks solution is to use external GFP. One GFP breaker is ganged to multiple PV input breakers, enough breakers to disconnect all arrays from all controllers. The outback solution, being external, will work for any mixture of controllers.
    BB. wrote:
    I believe that the DC GFI creates far more problems/issues than it solves.
    So true. After the GFP trips, all neutral DC wiring can be hot and unfused with respect to ground.

    There is a simple solution for one controller... use Outback's 3 pole GFP device to disconnect both PV pos and PV neg when a fault is detected.

    For two controllers you would need a 5 pole GFP (one pole being the ground fault detector and the other 4 disconnect pos and neg from two arrays), but I don't think they make one with that many poles.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po

    As I recall from posts years ago--The (then) Xantrex XW 60 amp MPPT controller put a current shunt the negative PV- lead to measure the current flow when doing MPPT calculations. So, for that controller--specifically, you cannot common bus the solar array PV- leads.

    Does this apply to the 600 VDC input Schneider/Xantrex MPPT controller--Don't know.

    Many (some/most/all???) MPPT controller do not place any current shunt/measuring hardware in the negative lead and therefore the negative PV- leads can be all bused together without issue (assuming you meet all of the other normal electrical design requirements).

    Don't know about Midnite--But I believe I remember reading a post where PV- common busing was specifically allowed for the Outback FM family.

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