Assuming both Main protective Bonding connections are in place, and your confirmation that Ze is good, I cant see there is a lot you can do.
Its always possible its originating from a neighbouring property with a fault maybe?
I watch this thread with interest.
MICC was quite common during my apprenticeship years.
One particular job was a famous stationary shop in New Bond Street, opening up the basement to extend the shop. The whole installation was Pyro (as was best known). I quite enjoyed dressing and installing it. Some old Pubs were also a common...
Someone getting in a bath when light is good, spending a long time in the bath until ambient light has decreased and whipping a door open to switch the light on before continuing to get dried etc.
Most normal people wont, but you cant fix stupid with some.
Edit: Not meant to be aimed at you...
If a switch is positioned just outside a bathroom, it will have the benefit of being more protected from a poorly ventilated room, but will not stop some dope opening the door and using the switch with wet hands.
It is untidy. Leaving the customer to get a second opinion was probably his biggest mistake. I'd say he'd best ask permission to return and sort the problem out himself. I realise his delicate position at the moment, so would a colleague be able to do this on his behalf?
There are a couple of...
You might start off with a global insulation test, and if any problems work down to individual circuit insulation tests. You also need to ensure there are no borrowed neutrals or interconnecting circuits. As already said in #2, go through all testing sequences, loose connections may also contribute.
Look into the Arduino, very flexible. There are many available programme strings available of this sort which can be altered very easily.
If your programming skills are not too hot the use of "XOD" is excellent.
Unknown to me, there are apparently class II construction shavers sockets - my bad.
However, whether it complies and the CE mark etc are genuine or not, it still looks of very poor construction.
https://m.japanese.alibaba.com/p-detail/Double-shaver-socket-for-mirror-60572223649.html...
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