Strange three pin plug socket

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Regarding HI earthing, I haven't committed the 17th to memory yet, but I'm as sure as I can be that the 16th stipulated two rings for the CPC. Is that wrong?

Without going into pages and pages again - all the guidance notes I have seen for the 16th edn regs (and the 17th) and the on site guide, also guidance by the NICEIC all indicate that a single ring can be if the certain criteria is met.
I think that is the NICEIC one that RF shows in the first one you linked to.
 
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Without going into pages and pages again - all the guidance notes I have seen for the 16th edn regs (and the 17th) and the on site guide, also guidance by the NICEIC all indicate that a single ring can be if the certain criteria is met.
I think that is the NICEIC one that RF shows in the first one you linked to.
A single cpc ring can be, but the certain criteria includes the ones in 543.7.1.3 (i) or (ii), so the cpc in 2.5mm² T/E does not comply.
 
When high integrity earthing first materialised, you used to see people in the wholesaler trying to get sockets, not really knowing what they where doing, and the wholesaler also confused and trying to sell them MK sockets with CLEAN earth terminals (two terminals, one for the actual earth pins and the other for the two securing screws for the building earth.)

It took a while for both sparks and wholesalers to understand the requirement, and manufacturers too. There is now a huge choice of manufacturers of DUAL earth terminal sockets.
 
It isn't normal in domestic installations so if you aren't into industrial or commercial you probably will not come across HI earthing.
It is used where earth leakage exceeds a limit such as an office where there are lots of leaky computers and monitors.
Basically it is ensuring the CPC is large enough so it isn't easilly accidentally lost or if the CPC isn't large enough it is backed up.
There's plenty to read about it here:
 

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