Certainly possible - for single phase it's just a matter of a better PE than N (e.g. due to parallel paths on the PE side - e.g. bonding to extraneous-conductive-parts shared with installations closer to the substation for instance).

3-phase SSC would of course be higher, so there would need to be a more dramatic difference - but still possible in a few cases.

Of course it might be useful to show that the PEFC is lower (e.g. because RCDs don't have the same breaking capacity).

   - Andy,

Andy,

I struggle to believe that a bolt 3 phase short circuit between all phases could be smaller in magnitude than a fault between any phase and earth

Thats why I refer to a 3 phase DB and not a 1 phase DB where I know that there are cases where the fault between L and E is higher than the fault between L and N

Cheers

Andy,

I struggle to believe that a bolt 3 phase short circuit between all phases could be smaller in magnitude than a fault between any phase and earth

Thats why I refer to a 3 phase DB and not a 1 phase DB where I know that there are cases where the fault between L and E is higher than the fault between L and N

Cheers

But you're taking L-N and doubling it - so if there's a reduced N in the supply somewhere (reduced N cables were quite common a few decades back - I guess there's still rather a lot still in service) - L might have rather less than half the impedance of your assumptions, so a small PE impedance might still bring the total within the same ballpark.

   - Andy.

In some industrial installations the parallel paths from various bits of metalwork: structural steel, pipe work, containment etc provides a much lower impedance path than the actual conductors.