Details of BS7671:2018 Amendment 1 are here.

AJJewsbury:

That to some extent is my gripe. The amendment aims to deal with the risk in single phase installations, but not 3-phase ones.

Yes, the new device described in option (iv) - based on the L-N voltage going out of bounds - is only permitted for single phase installations. From what I gather that's not casting any aspersions on 3-phase systems, but an acknowledgement that the approach is basically flawed as it is possible to have a combination of 3-phase loads and a broken PEN such that a L-N voltage is still within 230V+/-10% but the PEN is way over 70V from true Earth. If you do have a 3-phase system (and can't compare voltage with an electrode) you're far better off using one of the approaches in option (iii) - i.e. comparing with an artificial N point generated from all three lines (see A722.4) as that's far more reliable. So basically the most flawed approach is only allowed where there's no better alternative.

AJJewsbury:

That to some extent is my gripe. The amendment aims to deal with the risk in single phase installations, but not 3-phase ones.

Yes, the new device described in option (iv) - based on the L-N voltage going out of bounds - is only permitted for single phase installations. From what I gather that's not casting any aspersions on 3-phase systems, but an acknowledgement that the approach is basically flawed as it is possible to have a combination of 3-phase loads and a broken PEN such that a L-N voltage is still within 230V+/-10% but the PEN is way over 70V from true Earth. If you do have a 3-phase system (and can't compare voltage with an electrode) you're far better off using one of the approaches in option (iii) - i.e. comparing with an artificial N point generated from all three lines (see A722.4) as that's far more reliable. So basically the most flawed approach is only allowed where there's no better alternative.