Has anyone got any diagrams how RCDs and main switches are wired up in a consumer unit? That would really help! Thanks!
A main switch in a consumer unit is just that, the meter tails (or supply) are wired directly into the main switch thus switching it off will kill the power (Line and Neutral) in the consumer unit with the exception of what is upline of the isolator i.e. the meter tails and the top of the isolator.
An RCD is a device which monitors line and neutral currents, in a healthy circuit the current flowing in the line must equal the current flowing in the neutral. If a fault occurs and current flows to earth either by the Circuit Protective Conductor (CPC) or via a person the current in the line will not equal that flowing in the neutral. If the fault current exceeds that of the RCD trip level it will trip and disconnect the power.
In a consumer unit which has an RCD protecting a number of ways it is important that all circuits connected into RCD protected ways have their Line connected to the MCB in the correct rail and their neutral connected into the correct neutral rail for that RCD, otherwise an imballance will occur and trip the device. The CPC should be connected to the correct numbered way in the consumer unit earth rail for identification purposes, this is usually just a single rail. Some RCDs have a fly lead which also connects to this rail.