Carlo Gavazzi's ER4 is a single-phase full-wave plug-in power monitoring relay. It has four universal current/voltage inputs, relay output, and a built-in digital display for energy reading and alarms. It can be used for power monitoring and switchover applications in single phase or two wire three phase systems. The ER4 can be used to monitor parameters such as power, voltage, current, and energy, as well as alarms for overload and overvoltage, and is compatible with both AC and DC applications. It can be installed in power distribution panels or directly into a fuse box. The relay output allows it to be connected to an external circuit, and the digital display can be connected to either a 4-20mA current loop or a simulated mains voltage. Additionally, it can be connected to a modem/remote monitoring system, allowing it to be accessed remotely.