PV GFP

LOTW
LOTW Solar Expert Posts: 25
I want to install a Ground Fault Protector on my Outback FM-60 and MX-60, but the only one Outback has is the 80 amp version, while max current for the CC's is 60 amps. Is it normal practice to use the 80 amp GFP breaker set as the only protection between those charge controllers and the battery bus?

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: PV GFP

    As I understand, you connect the 80 amp (or 63 amp) DC GFI breaker between the PV Array + and then through a another appropriately sized breaker, then to the PV + array input to the charge controller... Not between the battery bank and the charge controller.

    Note that the DC GFI breaker is not really used to trip on the current. It is a "slaved switch" (two breakers are "ganged together" to a second ~1/2 to 1 amp breaker. That second current flow detection breaker is connected between the battery negative bus and the "earth ground". If there is a "ground fault" in the system that causes current to flow between the Battery negative and earth ground, the small breaker trips, which then turns off the "main breaker".

    The second breaker in series with the DC GFI Breaker on the PV array is actually the over current protection/ On-Off switch for the array. You don't want to use the DC GFI to turn on/off the array as this also would disconnect the safety ground too--potentially making the system unsafe (floating battery bus ground).

    You would connect a second breaker (again, appropriate size) between the Charge Controller and the Battery Bank. This breaker would be a single pole breaker with no DC GFI function.

    These breakers are available with "non-standard" rating/markings (as I understand). Normally, you would define the maximum continuous current (say 60 amps). Multiply that by 1.25 for the NEC safety factor or 60*1.25=75 amps minimum. And then round up to the next standard wire and breaker rating. I believe that Outback started by offering a "63 amp" breaker for use on a 60 amp charge controller. But the wiring should still be rated for >75 amps (as an example).

    Our host, Northern Arizona Wind & Sun does have 63 amp and 80 amp versions. From my point of view, the 50/63/80 amp DC GFI breaker just has to be greater than 1.25*Imp-array--otherwise its current rating does not matter--It is "just a switch". The smaller breaker (~1/2 to 5 amps) is what sets the "sensitivity" to earth fault current.

    Note: I have a big problem with DC GFI Breakers and think they are unsafe to use in a "typical" off grid solar power system--regardless of what the NEC says. Normally, you would never ever put a fuse or breaker in the main system DC safety ground.

    If you want to read the details "why" I believe this... Here is a discussion on the Midnite Forum:

    Ground Fault Protection

    The summary is that a solid DC Battery Bus ground to green wire safety ground (cold water pipes, ground rod driven into soil, connection to AC main ground, etc.), is usually much safer (for many reasons) than adding a DC GFI assembly because of the lifted ground (the DC GFI is intended to reduce the risk of arc faults between PV + and earth ground--But ARC Fault Breakers/circuitry does a much better job of this--in general--but there are still lots of details that affect final wiring choices). There is no "good/simple" answer here.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • LOTW
    LOTW Solar Expert Posts: 25
    Re: PV GFP
    BB. wrote: »
    As I understand, you connect the 80 amp (or 63 amp) DC GFI breaker between the PV Array + and then through a another appropriately sized breaker, then to the PV + array input to the charge controller... Not between the battery bank and the charge controller.

    Note that the DC GFI breaker is not really used to trip on the current. It is a "slaved switch" (two breakers are "ganged together" to a second ~1/2 to 1 amp breaker. That second current flow detection breaker is connected between the battery negative bus and the "earth ground". If there is a "ground fault" in the system that causes current to flow between the Battery negative and earth ground, the small breaker trips, which then turns off the "main breaker".

    The second breaker in series with the DC GFI Breaker on the PV array is actually the over current protection/ On-Off switch for the array. You don't want to use the DC GFI to turn on/off the array as this also would disconnect the safety ground too--potentially making the system unsafe (floating battery bus ground).

    You would connect a second breaker (again, appropriate size) between the Charge Controller and the Battery Bank. This breaker would be a single pole breaker with no DC GFI function.

    These breakers are available with "non-standard" rating/markings (as I understand). Normally, you would define the maximum continuous current (say 60 amps). Multiply that by 1.25 for the NEC safety factor or 60*1.25=75 amps minimum. And then round up to the next standard wire and breaker rating. I believe that Outback started by offering a "63 amp" breaker for use on a 60 amp charge controller. But the wiring should still be rated for >75 amps (as an example).

    Our host, Northern Arizona Wind & Sun does have 63 amp and 80 amp versions. From my point of view, the 50/63/80 amp DC GFI breaker just has to be greater than 1.25*Imp-array--otherwise its current rating does not matter--It is "just a switch". The smaller breaker (~1/2 to 5 amps) is what sets the "sensitivity" to earth fault current.

    Note: I have a big problem with DC GFI Breakers and think they are unsafe to use in a "typical" off grid solar power system--regardless of what the NEC says. Normally, you would never ever put a fuse or breaker in the main system DC safety ground.

    If you want to read the details "why" I believe this... Here is a discussion on the Midnite Forum:

    Ground Fault Protection

    The summary is that a solid DC Battery Bus ground to green wire safety ground (cold water pipes, ground rod driven into soil, connection to AC main ground, etc.), is usually much safer (for many reasons) than adding a DC GFI assembly because of the lifted ground (the DC GFI is intended to reduce the risk of arc faults between PV + and earth ground--But ARC Fault Breakers/circuitry does a much better job of this--in general--but there are still lots of details that affect final wiring choices). There is no "good/simple" answer here.

    -Bill

    Thanks for the info. The Midnite Solar GFP as you said goes between the PV array and the CC, but in Outback's manual for their gfp's, they specifically say do not put it there, and put it between the cc and the battery bus, and the diagram shows it as the only disconnect. In addition, I see in the FM CC manual now, it says use an 80 amp breaker for the FM-80, and an 80 or 60 for the FM-60. Different from the printed version that came with my fm-60 last year. This is why I am confused. Also I was under the understanding that when using Outback's breakers, you don't need the NEC 1.25 as they are continuous duty breakers? This is why I am confused, why is an 80 amp continuous duty all of a sudden OK on the battery side of an FM-60? I don't care too much about NEC, as I'm in Canada anyways, but I do want to do it properly.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: PV GFP

    Hmm... I see what you mean (PDF download).

    There are many reasons, in my humble opinion, why this is both unsafe and makes a single point of failure takes out multiple/all charge controllers--assuming that any single breaker in the "pack" turns off all breakers (and lifts safety ground except for a 43 kOhm resistor across the sense breaker--for static discharge I believe).

    From a ground fault control--It should not make any difference if the DC GFI is in front of, or behind, the charge controller (unless they controller is being protected against Hot to Earth ground faults too). Nominally, the whole DC GFI was to protect wiring failures (hot to earth fault) in the solar array wiring (as I understand).

    I would not do it. (that opinion and $5 will get you a cup of coffee:roll:).

    Regarding the continuous duty breaker rating--I am not sure what they did this--and if the breaker is simply a "re-marked" 80 amp breaker or if there is a real difference (internally) with a 63-64 amp continuous rated breaker and a standard NEC 80 amp breaker. :confused:

    In any case, from what little I understand, even with a "63 amp continuous rated" breaker you would want 80 amp rated wiring and for an "80 amp continuous rated breaker" you would want 100 amp minimum rated wiring.

    Regarding an 80 amp breaker on a 60 amp output (or input) solar charge controller... Remember that breakers are there to protect the wiring, not the device. So, you can have a larger rated circuit breaker and wiring without any problem (there is usually a maximum input rating to any electrical device--i.e., you cannot put a 1,000 amp breaker on a 100 amp maximum input circuit charge controller as this would be in-excess of the maximum design input current rating for the device--It can be hard to find this "not to exceed rating" for many devices).

    Normal NEC rated breakers are designed to never trip at 80% of rated current, and should always trip at 100%+ of rated current (that may take minutes to hours to trip at 100% of rated current). Between 80-100% of rated current is the "false trip" zone and you don't want to be operating there under normal conditions.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: PV GFP
    LOTW wrote: »
    The Midnite Solar GFP as you said goes between the PV array and the CC, but in Outback's manual for their gfp's, they specifically say do not put it there, and put it between the cc and the battery bus, and the diagram shows it as the only disconnect. In addition, I see in the FM CC manual now, it says use an 80 amp breaker for the FM-80, and an 80 or 60 for the FM-60.

    I too have wondered about the difference... Outback puts their GFP in the battery circuit rather than the PV circuit. It makes me wonder what is the NEC purpose of GFP... is it to disconnect the PV or the battery?

    When you do it the Midnite way, the 63 (or 80) amp breaker that is part of the GFP is not for over current protection. It is used as a disconnect and is triggered by the ground fault current in the smaller breaker. As a disconnect it just needs to be large enough to handle the current from your panels.

    The Outback approach is that the big breaker is both over current protection and a disconnect (when tripped by the smaller breaker). It needs to be able to interrupt the very high currents that a battery can supply into a short circuit.

    --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: PV GFP

    And when done the Outback way--Turning off the power to allow servicing of the charge controllers also lifts the safety ground too (as well as turns off all parallel charge controllers).

    I would suggest that each charge controller should have its own circuit breaker for servicing.

    And, in past NEC regulations, you are not ever supposed to use the DC GFI switch for "on/off" branch circuit control as this lifts the DC Safety Ground... And why you see the Midnite documents show both a DC GFI and a normal circuit breaker in series.

    In any case, the present DC GFI causes why more issues than it solves (and in reality, doing a fault analysis shows that the 1/2 amp circuit breaker is doing the Arc Fault suppression, it is not the "main breaker"--Which is totally counter to good engineering safety design which is 100% against ever lifting the safety/green wire ground--Why they require separate ground connections, double nutting, welded/swagged permanent splices for safety grounds, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • LOTW
    LOTW Solar Expert Posts: 25
    Re: PV GFP

    I think I will just not bother with the GFP all together.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: PV GFP

    For many folks, they have to go through a building department/inspector--It may not be so easy to "ignore" the DC GFI for those folks.

    Again, this is just my personal opinion--If you have any further questions/concerns, please ask. Not trying to "bully" anyone into seeing my position.

    If you are very concerned about solar array related fires and how to address the issues--The new "Midnite" combiner boxes with a "bird house" emergency array shutdown box is an interesting solution. Add that Midnite Classic controllers have Arc Fault detection/shut down, I would suggest that these are a much better solution (although, you are going to pay a lot of money for these features--I would guess).

    Running as much of the exposed wiring in metal conduit (if you have little nibbling roof top/array residing creatures) is going to address many of those issues. And making sure your electrical connections are done correctly (no "series arcs") will help too.

    DC GFI (stopping DC Hot to Earth ground arc faults) is not any related to the AC GFI we are all used to (that reduces the chances of electrocution from a user standing in water, etc.).

    There are also AC Arc Fault breakers for homes these days--They can be a bit of a pain. A few people here have said that their vacuum cleaner can trip those Arc Fault Breakers (the Universal/Brushed Motor is full of "arcs" at the commutator).

    Sincerely,
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • northerner
    northerner Solar Expert Posts: 492 ✭✭✭✭✭✭
    Re: PV GFP

    I was wondering how to deal with this as well. My CC is a Midnite Classic with arc fault detection, so I'm not quite as concerned in going without the GFI protection. Would a possible solution be to modify the GFI so that tripping the small breaker, would essentially make a sudden reconnection to ground (ie much like a double throw switch)?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: PV GFP

    Would be "interesting"... But there is nothing (that I am aware of) that is available today to perform this function. And I still don't like the momentary lifting of ground (switched ground). All it takes is a near by lightning hit to mess up the system grounding.

    I believe that somebody had an idea how this DC GFI could be made with existing "Listed" components (circuit breakers) to perform this function (or use Listed Fuses for electronic shutdown of some charge controllers).

    I think it has created more problems than a DC GFI (as implemented) could ever solve.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • northerner
    northerner Solar Expert Posts: 492 ✭✭✭✭✭✭
    Re: PV GFP

    A light duty transfer switch perhaps. Of course the electronics "to run it" would have to be very different from normal transfer switches, that usually deal with detecting AC power. But not sure if they make a light duty one though?

    At least the momentary lifting of ground would limit the time one could be zapped.:p
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,728 ✭✭✭✭✭✭
    Re: PV GFP
    BB. wrote: »
    Would be "interesting"... But there is nothing (that I am aware of) that is available today to perform this function. And I still don't like the momentary lifting of ground (switched ground). All it takes is a near by lightning hit to mess up the system grounding.

    I believe that somebody had an idea how this DC GFI could be made with existing "Listed" components (circuit breakers) to perform this function (or use Listed Fuses for electronic shutdown of some charge controllers).

    I think it has created more problems than a DC GFI (as implemented) could ever solve.

    -Bill

    My only exception to almost everything you write Bill is the case of an XW system with either the hi-voltage charge controller or the low voltage controller and GFCI. During lightning (nearby) the GFCI will tirgger and the Inverter will go into an escalating fault mode and shut down AC output. This has saved systems for a few folks and while there never is anyway to reliably make statements about lightning protection, I will sacrifice a little safety offgrid for a little piece of mind. I am sure there are other ways to impliment an automatic shut-down, this one does work!
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: PV GFP
    LOTW wrote: »
    I think I will just not bother with the GFP all together.

    It may be a moot point now, but perhaps they speced the 80 Amp breaker instead of a +25% one since DC breakers in that size were not easily available until recently, I think Outback and Midnite source their breakers from the same manufacturer, and panel mount breakers over 80 Amps just were introduced last year (I think) other than the larger breakers designed for inverters
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: PV GFP
    northerner wrote: »
    Would a possible solution be to modify the GFI so that tripping the small breaker, would essentially make a sudden reconnection to ground (ie much like a double throw switch)?

    What would work is to have the small breaker ganged to four other breakers that disconnect PV pos and neg and battery pos and neg. Of course that assumes there is only one charge controller. Add two more breakers to the gang for each additional controller.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i