Ah, maybe that was perhaps the same 'electrician' who, very many years ago (and just before I 'sacked' him) tried to vigorously insist that I needed a second RCD close to a shower, since, "by the time it got back to the RCD in the (admittedly fairly distant) CU" any leakage/imbalance current would have fallen to too low a level to trip the RCDBut getting back to electrical matters, I've actually had electricians tell me with complete certainty that the dividers between sections of trunking only insulate one way Yes, some believe that you can only put the mains in a certain section, and ELV stuff (e.g. my network cables) in another specific section.
Kind Regards, John