What is an RCD why is it not like a MCB trip switch?
In essence, a MCB ‘trip switch’ can protect against overload and fault currents. The level of protection is indicated by the rating of the MCB and is, for example, usually 32 Amps for a modern socket circuit. If the circuit is overloaded (e.g. too many appliances) the MCB will switch itself off to prevent danger. It will also eventually switch itself off if a significant fault occurs causing any live part if the circuit or appliance to come in contact with any metal casing, pipe-work or other structural metal. It requires relatively high fault currents to pass for it to switch off the electricity in the regulation time (faster than 0.4 seconds). To get such a large fault current to flow a very effective earth path is required, i.e. we need to be able to to ‘soak up’ all this electricity. In certain conditions it is not always possible to get a good enough earth path to do this (out doors, for example) and so we need something else to switch off the electricity in the event of a fault.
