Abstract: A neutral circuit current monitoring device detects at least one current level, which includes harmonic currents, flowing in a neutral circuit of a power distribution system such that preliminary warnings can be given to personnel operating the system before serious overload problems exist. Warnings can be given via audible and/or visual alarms and/or by electrical contacts which can be used to operate auxiliary devices. Preferably, two current levels defined by interchangeable secondary fuses within the monitoring circuit are detected with a first or low current level in the neutral circuit being calculated to also indirectly monitor for overheating of the distribution transformer caused mainly by circulating third harmonic currents in the transformer primary. The low current level permits personnel to investigate and correct a developing problem before it occurs. Preferably, a second or high current level of the current sensor can be set at a value less than 100% of the phase current rating.