As has been said, they certainly would not be compliant. If the customer is determined, and you were brave (Bakelite is a pretty unforgiving material to work on!), I suppose it might be possible to engineer a situation in which a 'tool' was needed (even if only by drilling a couple of holes in unobtrusive places and putting a cable tie through them)? A grub screw would be another option, but that would require even more frightening 'machining' operations!
Fair enough - but, if the alternative were to throw them out, you'd lose nothing (and might even surprise yourself!) by attempting some surgery! B22 'plugs' (the 'cover' just screwed off, like a lampholder), common in my youth, eventually acquired a little nylon grub screw to make them compliant with more recent regulations!As I thought then, thanks. I will go back to them with the options of expensive modern equivalents or good old white plastic! Don't think I will attempt operating on them John!
Using SELV and a relay has advantages such as being able to use alarm size cable for the switch drops which reduces the amount of chasing required.
Use DC for the ELV as over time relays with AC coils can develop irrrating humming sounds.
I would earth the negative side of the ELV so that any insulation breakdown fault in a relay ( Live to ELV ) would trip the RCD .
Depending how far you have got with the re-wire it may be of value to group the relays in clusters and use individual twin and earth to each lamp.
All my lights work this way to avoid chasing switch drops in the walls which are wattle and daub, lath and plaster or stone.
By connecting one side of the ELV supply to the "earth" and supplying it from an RCD protected LV source the regulations are sort of complied with. If there is a fault that brings the ELV circuits up to a mains voltage ( but still 12 volts across the output of the ELV supply unit ) then the RCD will trip so the safety the regulations are supposed to achieve is achieved.
If we're talking about the regulation concerning 'buried/concealed cable' then, as far as I can see, whether the ELV circuit is earthed (PELV) or not (SELV) (and provided it is isolated from the LV circuitry), by virtue of 522.6.204(v) and 522.6.202, RCD protection would not be required because the cable was buried.
Fair enough - but I still don't know what it was of which you said "there is no such thing".TBH I was going by (a possibly faulty) memory - I thought we established a few months ago that RCD protection was needed for ELV cables.....
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