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Neutral-Earth link is Island mode

David Slate

Hi all, quick questions.

Why the need for a N>E link in island mode?

If the system is TT or the back up part is, and L&N are disconnected by the inverter from the grid, once back up has switched, therefore supplying its own L&N why would that N need to be connected to the TT earth?

Or is the N>E link relay only necessary for systems that don't provide a neutral terminal on the back up side?

We have an Alpha Smile 5 unit. its provides a L&N in back up/UPS mode. Talking with Alpha this back up is effectively an IT network so requires a TT electrode for earth

Thanks in advance!!

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    IT or TT ? IT must not have an earth TT must, and TT also has an NE link, at the source. I'd be most surprised if you wired a UPS as a TT, normally TN-S.

    If there is no NE link, consider carefully what happens if there is a fault and the 'live'  output of the UPS is shorted to some nominally earthed fabric of the building ? What we do not want is that phase to then be earthed, and 'neutral' to now be at 230V to earth, and any other phase to be at 400V to earth, unless the wiring and ADS strategy has been carefully designed to still work safely that way.

    Mike.

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  • 0

    IT or TT ? IT must not have an earth TT must, and TT also has an NE link, at the source. I'd be most surprised if you wired a UPS as a TT, normally TN-S.

    If there is no NE link, consider carefully what happens if there is a fault and the 'live'  output of the UPS is shorted to some nominally earthed fabric of the building ? What we do not want is that phase to then be earthed, and 'neutral' to now be at 230V to earth, and any other phase to be at 400V to earth, unless the wiring and ADS strategy has been carefully designed to still work safely that way.

    Mike.

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