A current monitoring device (CMD) with a set of electromagnetic field sensors located within one or more grounded housings positioned within the combined electromagnetic fields generated by one or more electric power lines. The CMD includes electronics, typically located within the grounded housings, defining impedance networks that combine the measurements received from the field sensors to create output signal indicative of electric current values for the phase conductors. The housings can be conveniently attached and to transmission line towers, distribution line poles, and high voltage power line supports in transmission and distribution substations. The CMD controls response equipment, such as a circuit interrupter that responds to current disturbances detected by the CMD. The CMD may also include communication for sending the current values to a remote controller, such as a central control station, that implements a wide range of response equipment.