just a quick thing, there is a difference between an RCD and an RCBO. typically an RCD provides additional leakage protection for a number of circuits, each of these circuits have their own MCB. That's why when they trip (due to an iron for example) all the sockets in the house trip, even though there are three or four circuits, the RCD sits on top of them all and will kill power to all MCBs / other circuits it feeds.
An RCBO is a combined RCD and MCB, it acts alone, it only controls one circuit so when it trips only one circuit goes down, i.e a shower tripping will not kill sockets and a broken kettle wont trip the shower.
For most typical power showers like Triton T90 and the Mira elite range a 10sq cable and 40 Amp RCBO is required.
An additional Isolation switch, local to the shower is also required to allow someone to isolate the unit to work on it safely, and to provide a quick and obvious mean s to kill power to the unit.
Under no circumstances should an electric shower be installed without a double pole isolator as part of the circuit.
also sometimes with electric showers there is not enough water head i.e the water tank is too near to the shower, the greater the distance between the tank and a pump shower the better, this creates a semi constant amount of water with a bit of pressure behind it, 1 M is about the minimum I think.
Last edited by Stoner; 13-01-2009 at 23:10.