Multiplus II GX MCB sizing (48 / 5000 )

DIY
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1

I am replacing the charging side of an old Solax SU3700E, and retaining the PV side so nothing fancy. The configuration is as follows:-

o AC-IN connects through a two pole rotary isolator to an MCB in the consumer Unit.
o Current transformer connected MP II
o Existing 3.7kw solar connected to CU via an isolator and separate MCB (AC-IN side)
o AC-OUT 1 not connected
o AC-OUT 2 not connected
o 5 x Pylonntech batteries will be connected once settings have been made in the MP II
o It is my intention to set the AC-IN limit at 20amp

So there will be no passthrough from AC-In to either AC-OUT1 or AC-OUT2, the input to MPII is cabled on 4mm2 singles (39amp cable).

As there is no passthrough it would be possible to use a 25A MCB, however would it be better to fit a 32amp MCB, and should this be a Type B, or a Type C due to the potential inrush current.

Clarification would be a great help.

Steve W

2

I have done some fresh searches and it appears that the inrush current causes a B curve MCB to trip if the batteries are not connected. I hadn’t connected the batteries as I wanted to check the configuration and then connect the batteries (a bit of a catch 22).

The post in question is :-

Which MCB with MP2 5000 used for 3680 VA?)

Response 4 from Matthias Lange - M_Lange - Victron Expert

It’s not recommended to start the MultiPlus without a battery.
The high inrush current to charge the capacitors causing the breaker to trip.
If you connect the battery first that won’t happen and a smaller B breaker can be used.

I will connect one of the batteries and confirm that a type B is sufficient if the batteries are connected.