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Battery backup earthing - PME supply

vantech

Hi, 

I am installing a battery (Alpha ESS) to a PME system. 

The battery charges during off-peak and discharges during the day during peak hours. There is no solar. 

This relatively straight forward and will be notified to the DNO. 

The system features a back-up supply, where if the grid supply fails, a set of loads can be powered from a dedicated “backup” output on the inverter. This output is already separate from the grid input. 

The question I have is around earthing. When in normal operation the inverter is connected to the PME supply via the MET in the distribution board and the “backup” output is earthed through this connection. When the grid fails (outage, for example) my thinking is that the PME “earth” cannot be relied upon for the backup circuit (lost neutral for example). 

What would be the best course of action to resolve this situation? 

  1. Earth rod at the customer premises connected to the MET? 
  2. Rely on the manual and it’s wiring diagram? 
  3. Other? 
     

The inverter manual gives no indication. 

Thanks.

Battery Inverter Manual: 

https://www.alpha-ess.com/Upload/Images/20190814093353_165226.pdf

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    vantech: 
    Thanks for this. 

    I will ask the manufacturer for specifics. 

    If the inverter has an automatic relay creating the E-N link on mains failure, i presume a supplementary earth rod will then make the system complaint (at least from an earth perspective). 
     

    This would then form an island TN-S system for the inverters output?

    Thanks. 

    No!, you can't quite assume that. Whilst it may form “TN-S”, it has to also include a [compliant] switching arrangement to appropriately disconnect the DNO's neutral.

     

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  • 0

    vantech: 
    Thanks for this. 

    I will ask the manufacturer for specifics. 

    If the inverter has an automatic relay creating the E-N link on mains failure, i presume a supplementary earth rod will then make the system complaint (at least from an earth perspective). 
     

    This would then form an island TN-S system for the inverters output?

    Thanks. 

    No!, you can't quite assume that. Whilst it may form “TN-S”, it has to also include a [compliant] switching arrangement to appropriately disconnect the DNO's neutral.

     

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