Electricity meter and consumer unit on a wall in a house. The meter (black box on left) measures the amount of electricity used. It displays this information on a cylindrical number display, black and red, in kilowatts per hour (kWh). The large white box is a modern consumer unit, or fuse box. The old system of fuse wires has been replaced with miniature circuit breakers (MCBs) and the box also houses as residual current device (RCD). The MCBs and RCD protect electrical devices from excessive currents. Each separate circuit in the house has its own MCB. At a specific current the MCB will 'trip', breaking the circuit. The circuits are reset by using the switches.