Electric motor underload protection system

This disclosure relates to an underload protection system for an electric motor connected to first and second power supply lines, the lines being connectable to an AC power supply. The system comprises a line voltage sensing circuit connected to the first line and having a line voltage signal impressed therein, and an amplitude adjustment circuit connected to the voltage sensing circuit for adjusting the line voltage signal to produce an amplitude adjusted voltage signal. A line current sensing circuit is connected to the second line and has a line current signal impressed thereon, and a phase adjustment circuit is connected to the current sensing circuit for adjusting the phase of the current signal to produce a phase adjusted current signal. A phase responsive circuit is connected to the amplitude adjustment circuit and to the phase adjustment circuit for producing an adjusted power factor signal, and disconnect circuit is connected to the phase responsive circuit for disconnecting the power lines when the power factor is below a preset value.