near my consumer unit and the board which the supply head/meter is attached to (what's the name for this called again as I cannot remember)!! there is a RCD on the wall, which has 3 leads going into it (L N and Earth I suppose from the colours, red black and green/yellow)! a lead (with all 3 wires in one cable) then this goes off to my electric cooker! My question is, can 1 RCD be used for 2 applainces, eg my cooker and also a power/electric shower?? Or will I neeed separate ones for each appliance?