Electrical installation in an outbuilding

[ppppenguin]

Not 100% sure why but I think it's realted to neutral faults. PME is prohibited in various other situations too. Petrol stations for example. I think it's all to do with making sure that earth really does stay at earth potential. A neutral fault on a PME system can dump a lot of current into equipotential bonding conductors which is why they are sometimes bigger on PME systems than others. Keeping an exported PME earth at earth potential could be awkward under fault conditions.