gkenyon: 
 

AJJewsbury: 
 

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

Correct. Typically all the "Earths" are (DNO and local electrode) are permanently connected together - the DNO's can't be relied upon during a grid failure and the local rod becomes just another bonded extraneous-conductive-part when the grid supply is working. But in island mode all the live conductors (N as well as L) of the inverter are kept completely separate from the DNO's.

   - Andy.

Sorry Andy, whilst this would at first appear correct, you also need to disconnect the supplier's neutral from the installation for a number of reasons. Failure to do so can render RCD protection inoperative (or could cause nuisance tripping) … and that may well be important because of the reduced EFLI in island mode.

Further, the DNO won't like it if they isolate the PME main for maintenance, and potentially find voltage on it they weren't expecting.

Regardless, it's effectively a requirement of ESQCR.

Hi,

If the inverter makes a direct connection between earth and its “backup“ neutral output, the disconnection of live and neutral “backup” outputs would already be isolated to prevent feedback into the inverters “grid“ input (otherwise the grid input of the inverter would become live powering non-essential loads). 

So the inverter itself (at least the type I have posted) will disconnect incoming L+N from its battery back up output. 

If we installed a change over switch that disconnects L+N into the inverter, or indeed the whole installation, there would still be a permanent connection through the earth conductor (as this has been switched in automatically) on the intertevers backup output and the N-E link on the PME system (for example on the cut-out). 

Albeit the L+N can be isolated firmly, there will also be a ”link” of sorts between the PME connection, the ground rod and the N connection of the inverters output.

The inverter is designed to provide an instantaneous change over to prevent loss of power to essential loads, so the use of a manual change over is not required. 

What impact (if any) will the PME earth (inside the cut-out or the street, wherever the DNO may have done this) to neutral link have, with regards to isolation? 

Thanks. 

gkenyon: 
 

AJJewsbury: 
 

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

Correct. Typically all the "Earths" are (DNO and local electrode) are permanently connected together - the DNO's can't be relied upon during a grid failure and the local rod becomes just another bonded extraneous-conductive-part when the grid supply is working. But in island mode all the live conductors (N as well as L) of the inverter are kept completely separate from the DNO's.

   - Andy.

Sorry Andy, whilst this would at first appear correct, you also need to disconnect the supplier's neutral from the installation for a number of reasons. Failure to do so can render RCD protection inoperative (or could cause nuisance tripping) … and that may well be important because of the reduced EFLI in island mode.

Further, the DNO won't like it if they isolate the PME main for maintenance, and potentially find voltage on it they weren't expecting.

Regardless, it's effectively a requirement of ESQCR.

Hi,

If the inverter makes a direct connection between earth and its “backup“ neutral output, the disconnection of live and neutral “backup” outputs would already be isolated to prevent feedback into the inverters “grid“ input (otherwise the grid input of the inverter would become live powering non-essential loads). 

So the inverter itself (at least the type I have posted) will disconnect incoming L+N from its battery back up output. 

If we installed a change over switch that disconnects L+N into the inverter, or indeed the whole installation, there would still be a permanent connection through the earth conductor (as this has been switched in automatically) on the intertevers backup output and the N-E link on the PME system (for example on the cut-out). 

Albeit the L+N can be isolated firmly, there will also be a ”link” of sorts between the PME connection, the ground rod and the N connection of the inverters output.

The inverter is designed to provide an instantaneous change over to prevent loss of power to essential loads, so the use of a manual change over is not required. 

What impact (if any) will the PME earth (inside the cut-out or the street, wherever the DNO may have done this) to neutral link have, with regards to isolation? 

Thanks.