Many thanks Dingbat for your quick response.
I appreciate your candour and concern.! The answer to your 1st question is NO!
However, I am not as green as I make out. I re-wired my house 25 years ago, including elec shower. Of course, no rcd's or rcbo's in those days and thankfully never any problems. I know my limitations and will not do this unless 100 per cent confident.
To answer your direct questions - I am sure that it has both forms of protection, i.e. MCB current overload function AND voltage drop - earth leak detection. (These are my layman's terms but you will know what I mean.)
I cannot send you a pic, but details from the box are as follows. Makers are Felten and Guilleaume. Trade name Moeller? Fl/LS kombischalter Disjuncture differential. RCBO Interruttore combinato. (How is your German, French and Italian) 40A B 30mA Type-AC 1p+N 6kA 921972133 FL7-40/1N/B/003-6 JP43C is stamped on the front of unit. The leaflet describes it as a Combined Residual Current Device FL4, FL7-6. I am assured by my source of 25 years that it is correct. He did mention the cable size, and I am happy with original 6 square over a run of approx 15 metres. Shower is a Triton T90 8.5 KW tank-fed. Separate (single-pole? will check) switch fitted in hot press 25 years ago.
Initially there was no space left on the DIN bar for this new unit so, I have removed one MCB from the DIN bar (and busbar) and re-wired that circuit through another MCB of same rating which serves downstairs lights.. The removed MCB only served house alarm (.5 Amp?) so no overload on 2nd MCB.
This unit does not line up with the present MCB's on DIN bar. The bottom is offset - i.e. it is recessed further into the cu - therefore I presume that it is not to be supplied from the busbar, but have its own supply from main switch? All the switches align when the cover is replaced on cu..
I don't want to overload you with too much info and I have probably left out something important. If I am right about the top 2 terminals, how do I supply a live and neutral to the bottom 2 in such a way that only the shower is going through RCBO. For now I don't want any other items going through it which may trip the device. If and when I get it going OK for a while I will most likely run kitchen sockets through it also. (These serve the garden)
Thanks again,
Look fwd to your reply,
Bash (That name was already taken - hence The Real Bash!)