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Multiplus-II - Transfer Switch Overload Characteristics


We are looking to install a 3-phase setup using a 5000VA Multiplus-II on each phase in a residential property. The house is grid-connected and the grid is very reliable. The house loads are split across 3 phases and are currently protected by a 63A TPN MCB, in reality though, the current draw on a given phase is not expected to surpass 40-45A. The goal of the installation is primarily self-consumption. The backup capability is of course interesting/valuable, but there is no plan to run off-grid for any extended period of time. We have an existing 12.5kW 3-phase Solaredge inverter.

The recommended approach, I believe, in this scenario is to put critical loads on AC-out-1 and put everything else on AC-out-2, but this involves work on the existing electrical installation to split things out which isn't trivial and adds to costs. An alternative approach is to put everything internal to the house (no car chargers) on AC-out-1 which would simplify the installation. There are of course two caveats to this approach though:

1) When running off-grid (very rare in our case), we'd need to take deliberate care not to draw more than 18A/phase to avoid overloading the inverter.

2) When running on-grid (particularly when there is no PV generation) we'd be drawing a fair amount of current through the Multiplus-II transfer switches.


What are the specific overload characteristics of the transfer switch? The manual says to use a 50A MCB to protect the AC-in of the 5kA Multiplus-II, but it does not specify what type of MCB. So, this begs the question as to what happens if there is a draw of above 50A for a short period of time and what the overload characteristics are.

Is the 50A a maximum and therefore the design current need to be a fair bit lower and not complying with this can cause damage to the inverter? Or, is the 50A the maximum continuous design current and as long as the current draw doesn't trip the MCB on AC-in then there isn't an issue?

What MCB type (curve) is recommended for AC-in?


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Related Resources

MultiPlus-II Product page 

MultiPlus-II Manual

MultiPlus-II 230V Datasheet 

VE.Bus Error codes

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