AERL Earth Guard detecting Negative to Ground fault on MultiPlus II 3000/48

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Isaac Shannos asked Jun 27, '20

AERL Earth Guard detecting Negative to Ground fault on MultiPlus II 3000/48

Hello,

Installing a ground fault detection device (the AERL EarthGuard) which references PV +, PV- and Ground.

System is 250/100 MPPT, 3 Multi Plus II 3000/48 / 35-32s, Kilowatt Labs 3.55kWh modules x2.

It all works fine, but when I installed the Earth Guard, which was the last thing I did. It detected a fault between ground and negative. Which I've isolated to be coming from the MultiPlus II.

Is there functional negative grounding in the MPIIs? Is there an option to turn this off?

The AERL manufacturer said it could be a faulty unit.

Multiplus-II Grounding

2 |3000

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Answer 1 · 2020-06-27T12:42:29Z

Guy Stewart (Victron Community Manager) answered · Jun 27, 2020 at 12:42 PM

Hi @Isaac Shannos,

There is not a functional grounding connection between ground and battery negative on the MultiPlus-II. It doesn't exist so it cannot be disabled. The Ground relay that is adjustable (depending on grid code) is between AC Neutral and ground, not battery negative and ground.

Have you double checked the resistance reading yourself with a Multimeter? Or just relied on the EarthGuard?

If there a link between Negative and Ground, it could be due to a product, or installation fault.

The next step would be to diagnose installation or product with a troubleshooting process to isolate the Multi's from the rest of the installation.

You said you have already isolated it to the MultiPlus-II's, but to one or all of them?

Also you didn't mention Battery Negative as a reference point, only PV+ and PV- and Ground. I presume you haven't done any functional earthing of the PV array? and you have fully isolated that as well? Testing and isolating the Ground connection from the PV?

Remember the 3 phase online training and note in the 3 phase and parallel manual that there must be a continuous battery negative connection between the three units while the comms are connected between them on the VE.Bus. So be very careful when testing.

Lastly to make sure there actually IS a fault:

What is the sensitivity of the EarthGuard unit?

What is the actual measured resistance?

And what is the legal requirement where you are installing?

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Isaac Shannos commented · Jul 13, 2020 at 09:50 PM

Hi Guy,

Thanks so much for your quick reply. The situation resolved itself the following day somehow after physically disconnecting and reconnecting (for fault finding) every component of the system. Must've been a moody Earth Guard unit.

When this fault wouldn't go away, I was worried for a while because there are functionally earthed modules running through the Fronius Galvo. All good it turns out! The Earth Guard is attached to the 250/100 only, which caters for the battery side earth fault detection too.

PS Looks like you've sent my "lizard cage" job to Victron they've been in contact with me. How fun!

Cheers

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