Growatt SPF5000 - trips breaker when AC coupled (Aus 240v)

[Hyena]

Hi all,
I'm in the process of setting up my house to run off batteries as much as possible and only draw on the grid when necessary. I'm in Australia with our standard 240v system so there's no split phase shenanigans or added complexities like in the US.
I have a 48v 300ah battery and Growatt SPF 5000 ES. I've yet to connect the PV input but have tested the AC input (20A outlet in my garage) and it charges the battery as expected. I connected up the AC out today and it is now running my house off the battery alone but the problem is when it tries to draw from the AC in it pops the 20A breaker. The inverter displays the incoming AC voltage and frequency but trips when it tries to draw any current. It was fine before I connected the AC out to my house circuits so I'm guessing it's an issue with the neutral side?

The line/active wiring is connected only to the inverter AC out but the house mains earth and neutral wiring is shared with the inverter output. Do I need to isolate the inverter neutral from the remaining house neutral link ? I thought the inverter passthrough allowed the inverter and grid to run in parallel once the inverter is maxed out, but after reading some other posts here it sounds like that isn't the case ?

Any other suggestions ?
Thanks!

 

[sunshine_eggo]

If it's not a wiring/ground issue, it may be a charge/load issue:

20A * 230V = 4600W

4600W is the ABSOLUTE UPPER LIMIT OF YOUR COMBINED CHARGING AND LOADS. When drawing from AC, it is passing through to power the loads. That's why it's recommend a generator be 50% larger than the inverter rating to allow for both loads and charging.

 

[Hyena]

If it's not a wiring/ground issue, it may be a charge/load issue:

20A * 230V = 4600W

4600W is the ABSOLUTE UPPER LIMIT OF YOUR COMBINED CHARGING AND LOADS. When drawing from AC, it is passing through to power the loads. That's why it's recommend a generator be 50% larger than the inverter rating to allow for both loads and charging.

Thanks, I should have mentioned that it's not actually set to pull the full 20A - I have it programmed for 40A (battery) which is only 2400w. Plus it was running OK when testing from a standard 10A outlet so it shouldn't be that.

Can any one else comment on how they neutral wiring is set up ? Do they need to be isolated ?

 

[wattmatters]

I am NOT an electrician, so bear that in mind when reading my thoughts below.

Growatt SPF 5000 ES

This is an off-grid only inverter.

I thought the inverter passthrough allowed the inverter and grid to run in parallel once the inverter is maxed out, but after reading some other posts here it sounds like that isn't the case ?

The inverter can pass grid power through, but it is not designed to operate in parallel with the grid.

The circuits you supply from the output of the inverter must be separated from the grid. They absolutely must not be connected to the inverter's output and the grid supply at the same time.

If your circuits are wired with both sources in parallel then this is probably why the RCD is tripping, and it's a good thing too.

One way to isolate your off-grid circuits is to install a make before break transfer switch. That way the end circuits can be powered by the grid, or by the inverter, but never by both in parallel at the same time.

If you wanted to have an inverter to power home circuits in parallel with the grid then you would need a grid-tied inverter designed just for that. These are the normal type of solar PV inverter which most homes in Australia with solar PV have installed. They synchronise their output and operate in parallel with the grid. They also require formal approval to install and must be done by accredited installers.

I connected up the AC out today and it is now running my house off the battery alone but the problem is when it tries to draw from the AC in it pops the 20A breaker. The inverter displays the incoming AC voltage and frequency but trips when it tries to draw any current. It was fine before I connected the AC out to my house circuits so I'm guessing it's an issue with the neutral side?

If however your end circuits are actually isolated from the grid when being supplied power by the inverter, then there are a couple of other possibilities.

I had tripping not dissimilar to what you describe. It was cause by having more than one RCD breaker in the circuit.

All of my end circuits are protected with RCBOs. Over current protection and residual current protection in one breaker.

When my sparky installed the small off-grid AC distribution panel for me, he fitted an RCBO on the circuit which was feeding the transfer switch, which then ultimately fed all the home circuits. This meant that all my circuits effectively had two RCD protection devices in series. That often results in erroneous tripping of an RCD, and so it was for me.

Solution was simple, replace the RCBO on the AC output from the inverter with a regular over current breaker instead. Nuisance tripping ceased and I had no safety concern as all my end circuits were already protected with RCBOs.
.

Another possibility is the lack of earth connection you describe on the AC output from the inverter. That might be showing up as a ground fault and trip

If the inverter was sold as being compliant for use in Australia, then you should be connecting all three wires (active, neutral and ground) to both the AC input and output terminals. The inverter should have terminals for all three wires on both the AC input and output.