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brmurray avatar image
brmurray asked

Ungrounded Neutral in 3-phase System

Hello,


I understand from the manuals that Multiplus 3-phase networks must be Wye/Star, not delta. However, I should be able to run 3-phase delta loads from the legs of the star, since the line-line voltage would still be 400V. Such a concept is drawn below.

1610495156236.png

My question is, what to do with the neutrals? They much be connected for the Multis to reference each other, and they are grounded by the ground relay. As drawn, there is nowhere to place an RCD or ground fault interrupter.


What is the best way to power a 400V_LL, three-wire, three-phase load.


MultiPlus Quattro Inverter Charger3 phase
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2 Answers
Johannes Boonstra (Victron Energy Staff) avatar image
Johannes Boonstra (Victron Energy Staff) answered ·

Hello, the "unused" Neutral may remain floating, the fact that they will be connected to ground isn't relevant in your setup.

You may however use a 3p RCD if you want if the ground relay is active by the way.


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bjwtb avatar image bjwtb commented ·
That's a short and clear answer to the obvious question which the manual leaves us floating around with.


I'll give it a try with ABB ACS and Emotron FDU drives as well as a Hitachi TIG welding inverter.

Thanks Johannes!

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mvas avatar image mvas bjwtb commented ·
If you do not connect the Neutrals to Ground, then will your RCD be able to detect all ground faults?


In your case, your 3-Wire 3-Phase "Delta" Loads do not care that the AC Supply is 3-Wire 3-Phase "Wye".
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bjwtb avatar image
bjwtb answered ·

FDU manual recommends a B class RCD. It's running on the grid on a A class RCD now.

B class RCD's are generally recommended for VSD's and also for solar inverters.

Good to know for the 3ph setup.

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