Voltage asymmetry sensor CAM-11 is used for protection of devices supplied from a three-phase network (e.g. motors) against damage caused by loss of phase voltage or asymmetry of phase voltages. Value of asymmetry threshold is factory set to 55V. The sensor protects also against a symmetrical drop of voltage switching the relay off if the voltage on any of the phases drops below 150 V (regardless of asymmetry level). The device can be supplied from any phase what causes that the presence of voltage on one phase is sufficient to ensure full functionality. 4sec. shutdown delay and voltage hysteresis cause that the sensor is resistant to short-term voltage fluctuations.