18KPV won't invert. GFCI fried when AC disconnect opened.

[meltdowndave]

Working two issues, but perhaps they are related?

2 x EG4 Power Pros connected an 18KPV. No PV yet.

Brought online for the first time last weekend at my remote cabin. Off grid mode with AC charging enabled. Set to cycle between 56.2V and 47V before recharging from the grid.

It initially charged and discharged but the SOC and voltage were out of step causing a low voltage alarm at 27%. Batteries wouldn't charge above 77% and it wouldn't discharge at all after it stopped charging (possibly in Back up Only mode?).

Changing the battery type to lead acid corrected the charging issue for now, at least.

But it still won't output and discharge the batteries once the battery was topped off.

Thinking that it might somehow be stuck in Back Up mode, I opened the supply side AC disconnect to force the battery to discharge.

However, it did not.

I shut the disconnect and then noticed that the GFCI for my satellite modem was solid red and wouldn't reset. Typically that means the outlet is done for.

Since I then couldn't research from the cabin I returned home.

On the drive back I started thinking that perhaps there's a safety interlock in the inverter that's preventing it from outputting because it senses a wiring problem. The root issue could also kill the GFCI.

But the outlet worked fine before cycling the disconnect and the inverter generated AC until the low voltage alarm. Even after it stopped inverting it continued to pass AC from the grid. Other GFCIs still work. Also, I've remotely restarted the inverter several times this week and the modem came back online, meaning that the outlet that provided the power survived those reboots.

To be fair, the GFCI was "recycled" when we demolished another structure and was repurposed for a dedicated modem outlet. So it had some age to it and could have been ready to "pop" and something as simple as the surge from shutting a disconnect switch may have finished it off.

Am I overthinking this and the solution still lies in the settings or is the dead GFCI a bad omen?

 

[sunshine_eggo]

Where is your N-G bond?

 

[meltdowndave]

Where is your N-G bond?

Main load center, upstream of the inverter.

That being said....

My configuration mimics the Partial Home Backup with Backfeed Breaker diagram in the install manual.

But there's a modification. I added bypass breakers to the main load center and critical load panel. A series of mechanical interlocks prevent the critical load panel from being energized by both sources at the same time, it's an "either - or" arrangement.

However, the arrangement also means that the critical load panel has two grounds and two neutrals that aren't isolated.

The picture should help. The blue ink represents two hot wires plus neutral and ground coming from the main load center.

Essentially, the neutral from the grid runs directly to the critical loads panel via a "shortcut" and also takes the "scenic route" via the neutral lugs on the AC disconnect and inverter. Ditto with the ground.

The intent was to create a way to bypass the inverter, if needed, but I'm wondering now if I was only half as clever as I thought that I was and the two neutrals might have a difference in potential or some such.

But why did it work initially?