The consumer unit – always known as the “fuse box” in installation work. This is because it contained fuses, a piece of wire between two screws, that melts or “blows” in the event of a current overload. For example a short circuit exceeding the value of the fuse wire. The presence of these type of fuses are a good indication that the fuse box and possibly the wiring needs replacing. The modern overload device is an MCB (Miniature Circuit Breaker) which trips when a circuit overload problem occurs and can just be reset when the problem has been rectified.
Over the past few years the regulations on consumer units have become more stringent with special needs to avoid electric shock and fire. The most important change is that all circuits are to include an RCD (Residual Current Device) for supplementary protection against electric shock. An RCD is a device that detects an imbalance in the live and neutral supply above 30mA which normally occurs when there is an earth fault in the wiring.
If an exposed metal part becomes live due to a fault which, for example, could occur in an electric kettle or toaster and to avoid the risk of electrical fires, especially with older wiring, the RCD would trip if the fault current rises dangerously high. Consumer units are also now metal clad. This is to avoid the possible risk ,if for instance conductors become overheated to the point of causing a fire the metal clad unit is designed to contain the fire. This is a known cause of house fires with earlier insulated consumer units.
Reeves Electrical Limited recommend the use of RCBO’s. This is a combined RCD and an MCB in a single module. In this configuration if there is a fault on a circuit only that circuit is lost not several circuits or the whole house if the RCD is placed down-stream of those circuits.