TX 75E avatar image
TX 75E asked

Polarity protection Using Multiplus 2 with Schuko


I'm in the design phase my sailboats power system and was thinking about using a Multiplus 2 as the charger / inverter on the boat.

I know that this question has been up before but no satisfactory answer has been posted.

The manual states that it's important not to get the phase and the neutral mixed.

Normally this is not a problem most marinas has 16A 1-phase land power connection and its not a problem with them. The problem is that many marinas still have the Schuko connection only.

I know how to measure what is what, but I just know that there will be a time when I get in to port wet and tiered and there is only Schuko connection and I will forget to check and just plug the thing in.

The question is what will happen? I can live with it just not working and needed to switch the connection around, but I don't want to damage the unit. If there is a risk of damage does any protection device exist that can protect the unit from this?



Multiplus-IIsystem design
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1 Answer
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

Nothing will happen, it doesn't matter, the MultiPlus will work normally.

It's AC current, the polarity is switching 50 times in one second.

The reason for this warning is that if you plug it in wrong you will have the live wire on the neutral and if a circuit breaker trips you still have the live at the the device.

So what you should do is to use dual pole circuit breakers for the AC output and maybe add a dual pole switch at the AC input.

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bbmz avatar image bbmz commented ·
Couldn‘t there be a problem at the moment of connection (depending of the infrastructure of the marina)?

My spontaneous answer would be, that you create a fault-current at the moment of connection/synchronisation. The island-mode multiplus still has an active connection between PE and (island) N while you are connecting L (marina) to this. Or does the multiplus first opens the ground-relays and afterwards tries to synchronise?

Nevertheless this seems more an academical question. I agree that there will be no damage to the multiplus.

But be aware - never mess up with line and neutral in multi-phase (!) systems. This can (and probably will) destroy multiplus-inverters.

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TX 75E avatar image TX 75E bbmz commented ·

Ok, thanks for the answers.

In the current setup I already have a circuit breaker breaking both just to handle that problem with not knowing where the Live could be. Just wanted to make sure that the device is not damage if it happens.

Multi-phase is not a problem because the need is not there, or the infrastructure in the marinas to provide it. So this will always be a single phase system.

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ bbmz commented ·

After connecting a AC source the Multi/Quattro will start to synchronize it's output voltage and frequency to match the input voltage/frequency.
In the moment of the switch over the internal ground relay will be opened.

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Related Resources

Additional resources still need to be added for this topic

MultiPlus-II Product page 

MultiPlus-II Manual

MultiPlus-II 230V Datasheet 

VE.Bus Error codes