Electricity meters. Domestic electricity equipment mounted on a wall. There are three types of meters here, ranging from the oldest (lower right, with pointer dials) to the next oldest (centre, with a cylindrical number display) to the newest (centre right, white, with a liquid crystal display). They all measure the electricity used in kilowatts per hour (kWh), a measure of the energy used. Other electrical equipment includes a fuse box (upper left). Fuses break overloaded electrical circuits. The residual current device (RCD, centre left) is a newer type of fuse that trips (switches off) an overloaded circuit. It can be switched back on, unlike a fuse, which has to be replaced.