Correct a MCB, detects an over current fault and unlike a fuse is resetable. This will not prevent you being killed if you touch a live wire, unless you exceed the current. The MCB is to protect the house wiring against a fault and on lighting circuits a shorting bulb.dgwebster said:Most homes have a MCB installed at the fuse box, which detects current overload (eg you are drawing 30A on a 20A circuit, best to cut off the supply.)
WRONG WRONG. Please check your source. An RCD (residual current device) cuts the power if there is an imballance between the live and neutral conductors ie the current is returning to earth through you, rather than the neutral wire. Touching a live wire via an RCB will generally cut the power before it kills you. Been there done that, got the brown pants......dgwebster said:An RCD detects shorts in your circuits e.g. someone has stuck their hand into the live tank and shorted it to earth.
Getting water on a plug will not blow the fuse or may not even trip the RCD. If the water gets between the live and neutral it will just fizz and steam nothing will trip. However it will also probably make a connection bewteen live and earth which will be detected as a fault and the RCD cut the power.
Current UK 17th reg now have combined MCB and RCD on all wiring circutis including lights, thus if you have a modern house adding an extra RCD adds nothing as both will most likely trip at 30mA fault current.
My house is old 15th regs (I think) and has MCB's on each circuit and all the plugs protected by a 30mA RCD, thus my fish tank tripping kills all the plug power in the house. So I have no RCD and don't need an RCD on the tank as if it faulted house trip would trigger as well. If you really did want RCD protection then 15mA trip RCD (rather than standard 30mA) would be better as this would most likely trip first before the house 30mA.
Obvioulsy if you have a realy old house with wired fuses, then an RCD is a very good idea.
Even better is unplug all electrics before fiddling with your tank.
Below is a 17th edition house consumer unit with RCBO's fitted (combined MCB and RCDs) on all circuits.
This what a RCBO looks like.