[RE-wrenches] Outback radian inverter with FM 100 ground fault

[Kent]

Jay,

If there is a PV ground fault, putting a short across the fuse holder 
may cause damage by drawing an arc. Use a multimeter to measure voltage 
across the fuse holder (should be the same as measuring voltage between 
PV negative and ground); if there is no voltage then there probably 
isn't a PV ground fault or any ground fault at that time. If there is 
voltage, then you need to track it down. It isn't necessarily in the PV 
array - it could be a dc load or even in the battery. If the voltage 
exceeds the battery voltage, the PV array is the culprit. If you compute 
the proportion of the negative to ground voltage to open circuit voltage 
then apply that proportion to the number of modules, it should tell you 
about where to look. If you have multiple strings, isolate the problem: 
disconnect all of the PV negative connections and see which one gives 
you a solid voltage to ground.

Kent Osterberg
Blue Mountain Solar


On 1/19/2025 6:57 AM, Jay via RE-wrenches wrote:
> Question about the fuses.
>
> For testing could you put a short test wire across the ends of the 
> fuse holder and use a clamp on to test for current? Would it cause any 
> damage?
>
> Instead of potentially going through lots of fuses?
>
> Jay
>
>
>
>> On Jan 19, 2025, at 7:48 AM, Mac Lewis via RE-wrenches 
>> <re-wrenches at lists.re-wrenches.org> wrote:
>>
>> 
>> Hello Dana,
>>
>> Ground faults are tricky.  Here is how I would tackle this on a 
>> sunny day:
>> 1.  Visual inspection of array, looking for backsheet, wire damage, 
>> broken glass, critter stuff (nests and bite marks).  Look for water 
>> intrusion or evidence that water has been somewhere that it shouldn't.
>> 2.  Visual inspection of all splice boxes, checking for wire 
>> insulation damage, evidence of water intrusion and critter entry.
>> 3.  Probe voltage between +, - and Ground (do this at a string level 
>> initially, and isolate strings and do this at open circuit).  Any 
>> evidence of bouncing voltage readings, loss of voltage, not rock 
>> solid voltage suggests you may have a ground fault in that string.  
>> If its in the string somewhere, you may see the voltage bounce and 
>> read in some fraction of the string voltage.  This can tell you where 
>> in the string it may be.  FOr example, if you have a 5 module string, 
>> you may get a 3/5 voltage reading if the fault is near the 3rd module.
>> 4.  Turn off array at combiner and run continuity tests between +, - 
>> and Ground again (no gfp fuse).  If you have continuity, this may 
>> suggest a ground fault in conduit run between combiner and FM100.
>>
>> Good Luck, bring extra fuses!
>>
>> On Sun, Jan 19, 2025 at 7:07 AM Dana Orzel via RE-wrenches 
>> <re-wrenches at lists.re-wrenches.org> wrote:
>>
>>     Yes I have 2 FM100s
>>     Dana Orzel
>>     C: 208.721.7003
>>     E- dana at solarwork.com
>>
>>>     On Jan 18, 2025, at 7:08 PM, Kirpal Khalsa via RE-wrenches
>>>     <re-wrenches at lists.re-wrenches.org> wrote:
>>>
>>>     
>>>     Dana...
>>>     Do you have multiple FM 100s? If so only one should have the GFI
>>>     fuse.
>>>     Broken panel with water getting into glass?
>>>     Turn it off and wait 5 min and turn it on.  Usually clears it
>>>     especially if it's a faulty nuisance trip.
>>>     Have had numerous FM 100s give faulty afci errors.  Removing
>>>     the.afci boards always resolved this issue.  But of course check
>>>     all you connections leading to and from the cc.
>>>     Keep a few extra 1A gfi fuses handy....you may need a couple to
>>>     test it all out.
>>>     Keep us posted.
>>>     Good luck
>>>     Kirpal
>>>
>>>
>>>     On Sat, Jan 18, 2025, 2:40 PM Dana Orzel via RE-wrenches
>>>     <re-wrenches at lists.re-wrenches.org> wrote:
>>>
>>>         Hey, all you wise ones,
>>>         37 years in the business and I’ve never had a ground fault
>>>         ever in any installation I’ve done or my home systems. I
>>>         went out to my system here an hour ago and one FM 100 is
>>>         completely turned off claiming ground fault on the mate 3S.
>>>         I guess my first question is :
>>>
>>>         Is this really a ground fault ?
>>>
>>>         I had removed the ground fault breaker when I upgraded due
>>>         to space considerations
>>>
>>>         In my entire time in this business, I’ve never had to deal
>>>         with the ground fault any suggestions on how I should be
>>>         tracing this?
>>>
>>>         Has anybody seen this in an FM 100 when it wasn’t a ground
>>>         fault?
>>>
>>>         I do own a megger&  I’ve never had to use it. I only bought
>>>         it about three months ago cause it seemed like a good idea
>>>         and I might need to use one someday, Maybe I’m psychic ?
>>>         now if I could just figure out how to trace this out.
>>>         All suggestions welcome thanks all!
>>>
>>>         Dana Orzel
>>>         C: 208.721.7003
>>>         E- dana at solarwork.com
>>>         _______________________________________________
>>>
>>
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