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Juhani Lehtonen avatar image
Juhani Lehtonen asked

AC Input current limit to protect the main fuse and the panel Amp rating

I am planning on adding 2 more identical Multiplus II 48/5000/70-50 to my system in Finland. I have tested a single MP for a year now with ESS.

It is a grid tied setup. My worry is that my main panel is rated to 3x35A as are my main fuses.

If I DO NOT have power assist enabled(checmark not selected in VEConfigure), will the Multiplus inverters overload the main fuse panel if I overload the house loads?

Or is powerassist just used with a generator?

I would like to think that without powerassist the system wont go over the total system current rating(being the same as the AC input limit), but could someone confirm?

In theory with the car charger, Bitcoin miner, 2 washing mashines, dryer, coffee maker, microwave, stove, oven and all the miscellaneous other appliances, I could go over 24kW.

Thou not likely. But with one single phase that could happen If I happen to stack up on a single phase.

If I would overcharge the panel in total and Multiplus starts to limit my "AC input current limit" from grid, will the multiplus then start to push extra amps to the panel from the battery bank, making it go over the rated amperage and start to overheat the panel bus bars?

Multiplus-II
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Juhani Lehtonen avatar image Juhani Lehtonen commented ·

To put it simple. I am looking for a way to have a Max A value for the AC loads which is 34A when having Fronius 10kW PV + Grid 3x35A + Multiplus inverter as possible sources for that power. If that is even possible.

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Duivert NL avatar image
Duivert NL answered ·

If you set the AC in current limit, the system will not go over that limit, but why do you have power assist off?


Power assist can help the system to power heavy loads if your house is on AC out on multiplus


When grid is feeding the loads with an ac current limit on ac in, the battery/pv will support when there is a heavy load

If the system is inverting (powering your house from PV and or battery) with a low or negative grid setpoint, and a heavy load kicks in the grid will support the inverter



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Juhani Lehtonen avatar image Juhani Lehtonen commented ·

It's off just as a test. Might turn it back on.

Can you please confirm what you said?

"f you set the AC in current limit, the system will not go over that limit".

So if I set the multiplus having a AC in current limit of 33A, my system will in any situation pull more amps(in total) to the fuse panel? Even if there is PV available for 16 more amps and the house has more than 34A of loads asking for power. So that 34A current limit is dynamic divided to the Grid + PV + Inverter?

How I understood it from the manual is that it only limits the AC in Amps, not for the rest of them down stream of the power sources. Like the Fronius PV.


There is also an option for Dynamic current limiter, but the manual says that it is intended to be used with generators. Not with grid.

I'm not sure if I'm making myself clear on the matter. I am not worried about any other part of the house electrical system other than the 3x35A rated main fuse panel and it's bus bars overheating/melting.


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Duivert NL avatar image
Duivert NL answered ·

Ac in current limit is there to keep the power draw from grid to the set maximum, so if you set it at 32A, the system wont pull more then 32A and will power assist from battery or DC pv when more is needed at ac out (if power assist is on)

If your fronius is on ac out of the mutliplus then power from there will go in your house loads first, then battery if needed and last surpluss is feed back in grid ( if that is allowed)


This will of course only work if the house loads are connected to ac out of multiplus, not in grid parallel topology


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Juhani Lehtonen avatar image Juhani Lehtonen commented ·
Thank you for the effort in answering. So it is as I already figured, that I just need to tightly keep an eye on my loads and replace the main panel if there are instances where the total load per phase goes near or over the rated limits because of multiple sources.

I will setup the house so that all the loads are after the AC-out that is relying on the battery backup and hence monitored for consumption. Also the Fronius AC inverter will inside the said backup so it wont shutdown if the grid goes down. 80kWh of LiFePo4 should be plenty to keep the house up for extended bits with 30kWp MPPT + 10kW AC PV.


I just hope there was a notification alert that I could setup if such overload situation occurs on AC loads. Perhaps I need to study the NodeRED system and build one custom.
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