ground-fault - Electrician Talk - Professional Electrical Contractors Forum

Hal260 · 05-17-2012, 08:11 PM

I'd like to ask for input and ideas relative to a possible ground-fault problem. I recently was called out to troubleshoot a residential PV system that had four (4) 2.5KW inverters. Three (3) of the inverters were inoperative (red lights + error codes). The two AC line fuses in three inverters were blown. I replaced the fuses with the following results: 1) inverter #2 of 4 came online and has remained online for a week now without any problems; 2) inverter #3 of 4 blew not only the two (2) ac fuses, but also blew a ground-fault fuse - it is completely inoperative at this time; 3) inverter #4 of 4 came online, but has both a green and red light indication with an error code that indicates there is a heatsink error. I got with the manufacturer and they sent me two (2) replacement inverters to replace inverters #3 and #4. I think simply replacing inverter #4 will bring it online as I believe the problem is / was internal. However, my big concern is inverter #3. I do not want to replace the inverter and have it damaged by the same problem that took out its predecessor. So, what I am looking for is any and all troubleshooting ideas you can think of to help me identify and fix the apparent ground-fault problem. Thanks.

Hal260 · 05-30-2012, 11:44 AM

Well, I didn't get any posts to my question, but I'll tell you how things worked out in the hope that it may help someone else out there. To recap, there were two (2) inverters that were being replaced (inverter #3 & 4) by the manufacturer. Inverter #3 was blowing all three (3) fuses including the ground-fault fuse. Inverter #4 was giving a heatsink error message.
My concern was that I did not want to replace the old inverters with new inverters and have an external circuit related problem (like a ground-fault) damage the new replacement inverter.
Well, in addition to taking voltage measurements I decided to swap the two bad inverters, that is, remove bad inverter #3 and reinstall it into position #4 and to do the same with bad inverter #4 by re-installing it into position #3. Because the inverters had different problems I figured that if the symptoms did not change the problem was internal to the inverter and it would be safe to install the new inverter(s) without worry of damaging it. If, for example, former inverter #4 (heat sink error) now in position #3 experienced a ground-fault and blew the fuses (like the former #3 did) then the problem was external and would need to be remedied before installing the new inverter.
Well, long story short, the symptoms did not change indicating the problems were internal to the inverters and "green lighted" the installation of the new inverters - which were installed without any problems experienced. So, the story has a happy ending.

woodchuck2 · 05-31-2012, 08:18 AM

I am curious of why so many inverters? How are the inverters wired together or are they separate? I have only worked on a couple of these off-grid systems but they always had one inverter. Both of these systems were Magnums with one inverter and one chargers and an AGS controller.

Hal260 · 05-31-2012, 01:23 PM

I'm in California, but noted that you are from NY (Adirondacks); I graduated high school in Plattsburgh, NY, so am a fellow New Yorker.

First, you assumed ... this is NOT a stand-alone system. It is a grid-tied system. It is almost a 10KW PV system (on an attorney's home) in Palm Springs (think lots of air-conditioning). I am not the original installer so am not sure why they opted not to go with a single larger inverter. They are PV Power brand inverters. Maybe they got a better price on the smaller inverters. I am sure it was something like that. Each inverter receives two series strings. So eight (8) series strings in all, with 9 modules per string. The AC output is, of course, paralleled at the main service panel bus bar (with AC disconnects in between) via backfed breakers. So, the inverters are not wired together (prior to the main service panel).

mcclary's electrical · 05-31-2012, 02:53 PM

Quote:

Originally Posted by Hal260

I'm in California, but noted that you are from NY (Adirondacks); I graduated high school in Plattsburgh, NY, so am a fellow New Yorker.

First, you assumed ... this is NOT a stand-alone system. It is a grid-tied system. It is almost a 10KW PV system (on an attorney's home) in Palm Springs (think lots of air-conditioning). I am not the original installer so am not sure why they opted not to go with a single larger inverter. They are PV Power brand inverters. Maybe they got a better price on the smaller inverters. I am sure it was something like that. Each inverter receives two series strings. So eight (8) series strings in all, with 9 modules per string. The AC output is, of course, paralleled at the main service panel bus bar (with AC disconnects in between) via backfed breakers. So, the inverters are not wired together (prior to the main service panel).

Around here, a system larger than ten kw requires you to become a utility and subject to at least a 79 dollar monthly surcharge