For an electrolytic cell, an apparatus and method are described that use one or more sensors to measure magnetic field strength about a conductor carrying electrical current. A processor is in electrical communication with the sensors and determines a compensated magnetic field strength based on the magnetic fields of other conductors that also carry electrical current to or from the electrolytic cell. The processor uses this compensated magnetic field strength to determine the cathode electrical current carried by the conductor and to identify open and short circuits between the anodes and cathodes of the cell. The described apparatus and method account for interactions between the magnetic fields of the neighboring cathodes.