DNO guys did not take any readings, just looked at the service. The garden room co will be paying the electrician and yes I've paid them minus a few hundred quid.
Could it be that the electrician measured a high Ze and the DNO bloke either just looked at the service and never took a loop reading, or did so with the bonding in place.
Just to give the flip side.
of course if the electrician explained his reasoning for wanting a PME terminal it would save everyone a lot of guessing!
That's correct. In both cases the 'S' means 'Separate' (separate neutral and earth).
In contrast TN-C means 'Combined neutral and earth' and, since that combined neutral and earth splits into separate neutral and earth after entering the premises, is gains an extra 'S' and becomes TN-C-S - usually refered to as 'PME'. PME stands for 'Protective Multiple Earthing' and, although it's not (electrically) an inevitable feature of a TN-C-S supply, a TN-C-S supply is not allowed in the UK unless it has PME, so 'PME' is commonly used to refer to this sort of supply.
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