It would be a type of TN system. Whether RCDs would operate or not is one question (you'd need to know the source impedance to determine 100 %, but probably except in certain cases where the RCD has an FE connection) - however, whether the RCD test button will operate is a further question. Where the test button circuit uses outgoing line and incoming neutral, there should be no problem, but where FE is used for the RCD, possibly not.

vantech said:

The article states this is a TN-S earthing arrangement if a reference to earth is made using a rod, however I note there is no N-E relay/bond. 

Whilst this arrangement is used in certain situations, it is not suitable (at least as shown) for Prosumer's Electrical Installations for systems that are sometimes connected to the grid, and sometimes battery, as discussed in Chapter 82.

The reason for this, is that, in connected mode there will be an effective "fault" between Line or Neutral (swapping 100 times per second), and this will operate RCDs. It is also contrary to the general requirements of BS 7671 and also, effectively, ESQCR.

To make this work in a Prosumer's Electrical Installation, the N-E bond relay would be required between MET and the battery mid-point. BUT opening the battery mid-point in connected mode means the battery floats - meaning the DC side would need to be double or reinforced insulation or equivalent, rather than "TN-S DC".

And it is that reason why the IET CoP for Electrical Energy Storage Systems shows the N-E bond being made to the AC Neutral.


There are, perhaps, ways of making a TN-S DC battery work, but it would require isolation in the inverter (and still an N-E bond to AC Neutral), or an arrangement where the battery inverter is only used when the grid fails - although the latter is really a type of UPS that has a "break before make" transfer and therefore not really ideal for either UPS or for energy storage in a prosumer's electrical installation.

Thanks for your input 

Thanks for your input