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ty-web avatar image
ty-web asked

2 x Multiplus-II 48/5000 in paralell.- connections

I have 2x Multiplus-II units I want to parallel. they are same vintage hardware. I have 5kw of AC coupled PV with Fronius, all currently working with one unit.

Q1. When both outputs are paralleled at the sub board, do I need to set one of the Multies to NOT close the earth neutral relay?

Q2 I have run in both Output cables and they are the same length, but the cable supplied only has a 2.5mmsq earth in the cable. So Iam thinking I need to run separate larger earths from the swb earth bar to both Multies. does this need to be the same lenght for both?

thanks in advance.

System is offgrid, however there is a change over switch to align the house to the Grid should there be a multiplus issue. Hence I need to use the Neutral Earth relay.

Multiplus-II
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2 Answers
Mike Dorsett avatar image
Mike Dorsett answered ·

Q1: For the earth relay, no you don't need to change this behavior.

Q2: each multi should have a 4 or 6mm earth bond from the stud to the earth bar, and these do not need to be the same length.

With parallel inverters, you need to try to balance the resistance in the AC path of each inverter and also the dc path. Over-sizing the cables is not recommended as this decreases the resistance, making it harder to balance.

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ty-web answered ·

Thanks Mike, I was aware of the AC cable and the DC cable requirements, thanks for confirming this. I have run 10mm Sq Earth to the studs, they are both equal length, but after your comments I can shorten the closest one by 3m, which I have had to loose in the wall and duct as I have done with the AC cable.

Thanks for taking the time to reply, you have answered my questions perfectly.

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