The WITT CM 3 is a self-resetting cable monitoring device for the detection of cable faults. A delay of 4.8 seconds is integrated between the signal and the triggering.
The device is used to monitor the insulation of cable systems in DC systems. It works without auxiliary voltages. The connection is made between the insulating outer jacket and a reference earth. Two potential-free changeover contacts are available for the message. The device is built into a plastic housing that can be mounted on a DIN rail.
The voltage between the cable jacket and earth is taken off via a rectifier. As soon as this voltage rises above an adjustable threshold, the signal relay responds. The circuit works according to the constant current principle, i.e. even if the voltage rises to 1000 V or more, the current requirement does not increase any further. The leakage current that flows to earth is very low at 2 mA; the current load only increases to 6 mA in the event of a fault. The switching status is displayed locally via a signal lamp.