Christian McArdle wrote:
I'm sure I should know - but what is PME ?

It stands for Protective Multiple Earth and is an obsolete term for
describing what is now known as TN-C-S. These letters, which are based on
French indicate that:

T - earth is related to ground potential. (alternative being I- isolated)

Silly question - is this 'ground', as in the big ball of stuff we're all
sitting on?