GroWatt AFCI on 10kw Grid tie

[sbalak]

I need some help to understand AFCI (arc fault circuit interrupter). My setup consists of 3 strings. Each string contains nine (9) 400w Canadian Solar panels. I use Tigo RSS shutdown modules. The first 8 panels use 4 Tigo TS4-A-2F modules, but the 9th uses a single TS4-A-2F module. All the panels are on the same roof face so they all share the same ground. I have a 10kw Growatt inverter (MIN10000TL-XH-US) is errors out for a ground fault (200 AFCI). Growatt support has said they're having some issues with AFCI and so I've done a couple rounds of firmware upgrades and settings changes, but ultimately I can't reach 10kw of consistent performance.

I'm trying to track down if I actually have a ground fault or if I have an inverter problem. Each of my strings outputs about 297v. When I measure negative to ground for each string I get between ~1.0vdc to 0.08vdc. I think the variation is due first string's positions on the roof. The highest makes slightly more than the middle. The middle makes slightly more than the bottom.

Is some voltage between negative and ground "normal" or since it's no 0.000 this confirms I have a ground fault?

Thanks for the help.

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[BentleyJ]

All the panels are on the same roof face so they all share the same ground.

There are 2 types of earth ground:
Equipment Ground. The PV racking and frames should connected to the earth which originates in the electrical panel. This satisfies the requirement for an Equipment Ground.

System Ground. Neither the Neg or Pos side of the PV output (System) should be connected to earth ground. This is sometimes referred to an "ungrounded system" where System is referring only to the electrical circuits where current flows.

Is some voltage between negative and ground "normal" or since it's no 0.000 this confirms I have a ground fault?

The only way there would be zero Volts between negative and ground is if they were connected.
They shouldn't be, so by definition it is normal for there to be some potential on BOTH the Pos and Neg PV DC as compared to earth ground.

 

[MajicDiver]

When I measure negative to ground for each string I get between ~1.0vdc to 0.08vdc.

Are you certain you have negative and positive correct in your discussion?
I just triple checked mine. I have anywhere between 5 and 12 vdc between PV positive legs and ground. I have string voltage between PV negative and ground. Others on this forum have discussed at length that one leg of the PV is referenced to ground by inverters and it can vary by manufacture. We have the same inverters, mine is the 11.4.

The only times I’ve had the AFCI trip is when our well pump was running which is only couple of times a week in summer, the reason is the power for it is sharing 3 conductors of a 5 conductor cable, the other 2 are a PV string. I leave the AFCI off over the summer, and up until this year turned on in fall but I never turned it back on last fall, partly because of reading of people having problems on this forum.

By the way, I just installed more panels and am in process of laying additional wires in trench to those and the string that shares conductors with the brushless DC pump. I never liked sharing conductors but had no choice at the time and am finally getting it right.