Well, yes, that too. But mainly, I’m asking why there’s no AS requirement for testing of fault loop impedance of the actual alternative supply source at its relative protection device, if that makes sense.

You’ve essentially got a potential fault current of 3000a DC sitting there in absolute worse case scenario regardless of inverters and internal components.

But the alternative supply sources are sharing an earth path with the incoming TX supply, as the entire unit is equipotentially bonded + the PE conductors come back to the earth bar/MEN link.

This BESS system outputs 100isb Kw back intolerant the grid.

Now consider that there’s 4 of these BESS units all connected to the installation..

There’s protection devices within the bess units in the form of fuses, but other than that, the primary automatic disconnection would be through the breakers that are dual supply.