UK RCOCB BS 4293

[banny07]

Hi Guys.
I went to see a job today where customer wanted to replace front plate of sockets and switches. Switches has no cpc but cpc is present in the cieling roses. As I opened consumer unit the main switch was 80A 2 pole RCOCB bs 4293 which has 100mA rated tripping current and 2000A breaking capacity. My question " Is it acceptable in dwellings". customer doesn't want to upgrade consumer unit. Please advise . Thanks in advance

 

[timhoward]

If the RCD works, I'd get on with it and get out of there!
If it doesn't, this is one where you could easily open a large can of worms that I'd personally choose to keep shut. It would be a rather challenging CU change if it turns out to be required. (Inset CU and looks like conduit for CPC). It's fairly likely the 100ma RCD is for fault protection of a TT system, or maybe it was TT once and is now PME.
I'd do a Zs@DB (remembering there could be parallel paths). If inconclusive I'd test local incoming earth (disconnected) with main switch off .
If I got higher that TNS numbers back I wouldn't get involved beyond advising in writing to customer that the fault protection of their installation couldn't be confirmed and more work is needed to investigate and rectify.