R.C.D Explained
A residual current device (RCD) is an electrical device that disconnects a circuit whenever it detects that the current is not balanced between the live conductor and the neutral conductor.Such an imbalance happens when a person or livestock is grounded and touches an energized part of a circuit (faulty socket or appliance).In normal conditions with no RCD the person would recieve a severe electrick shock, RCDs are designed to disconnect quickly enough to mitigate the harm caused by such shocks.Therfore RCDs are a must for electrical safety in nearly all installations or upgrades.
New 17th Edition dual RCD consumer unit
The 17th edition wiring regulations now states that almost every circuit in a new installation must Have RCD protection and the Electrical safety council advises anyone planning on getting any electrical work done should consider a consumer unit upgrade if there existing consumer unit is not RCD protected.RCD consumer units can be very sensitve and Sometimes you may get nuisance tripping caused by light bulbs blowing etc.If this is the case, once the lamp is changed the RCD should have no probems going back on.Thats why in the 17th edition consumer unit you have two RCDs in place protecting two banks of circuits, so if one bank trips the other stays on preventing total darkness when trying to locate the consumer unit.