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

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  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    ChrisOlson wrote: »
    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

    You're correct about the classic. Outback does it that way also. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    vtmaps wrote: »
    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
    And the three+ pole DC GFI only works for DC shorts on the PV array side of breaker (i.e., a DC PV short to earth that draws more than 1 amp) because the breaker only cuts off the PV source of power.

    If there is a DC to earth fault anywhere else in the system (battery to earth, inverter to earth, MPPT charge controller to earth, any other wiring fault to earth)--There is no other two pole breaker to stop those sources of power at all (i.e., short the battery + to earth, DC GFI does nothing to "interrupt" the source of the fault's power).

    Just a big mess--There are a dozen major fault situations where DC GFI does not work or causes more problems than it fixes).

    The only reason DC GFI even sort of works--There is a 1 amp fuse between DC Return and Earth Ground that stops current flow... But, in normal AC and DC wiring with single pole breakers/fuses, placing a fuse between return and safety ground is never a supported configuration (except in solar power systems). If you have a (now) floating power system, you need two pole ganged breakers on every power source to "safe" the system if there is a fault.

    Which then would add costs (more breakers with slave trips) and--If there is ever a hot to earth fault anywhere in the DC power system--It kills power to the entire DC power system.

    Just as bad as slaving the Main House Breaker to every breaker in the panel--Any fault kills the power to the whole home--killing power/lights everywhere in the home and making it very difficult for fault isolation.

    When design larger Computer/communications systems, putting fuses in the return/safety ground leads would have made my job a lot easier--The customers a lot less safe and the systems much less reliable.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ChrisOlsonChrisOlson Banned Posts: 1,807 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    BB. wrote: »
    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.

    Ah. Never thought about that. If that's the case then I'll have to separate out the PV- on the array that's going to feed the XW-MPPT-60. Thanks for pointing that out, Bill, as I believe you're right on that point.
    --
    Chris
  • YehoshuaAgapaoYehoshuaAgapao Solar Expert Posts: 280 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    ChrisOlson wrote: »
    Ah. Never thought about that. If that's the case then I'll have to separate out the PV- on the array that's going to feed the XW-MPPT-60. Thanks for pointing that out, Bill, as I believe you're right on that point.
    --
    Chris

    Xantrex and BlueSky controllers do not support common PV negative. Don't remember where I got that from, Think it was the Midnite Solar combiner box manual. I assumed it was over the GFCI because the manual wanted you to keep it in for only one controller.
  • YehoshuaAgapaoYehoshuaAgapao Solar Expert Posts: 280 ✭✭
    Re: Question about generator grounding - 2 chassis bonds going to different grounding po
    ChrisOlson wrote: »
    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

    James hated everything about where Xantrex put the grounding terminal and GFCI fuse in their charge controller. You will need some mighty fine fingers to get a #6 in there (Also, southwire THHN is very stiff wire).
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