The CFM is a self-resetting cable monitoring device for the detection of cable errors. Between Signal and triggering a time delay of 4.8 sec is integrated.

The device is used for the monitoring of the insulation of DC cable systems.  It works without auxiliary power supply. The connection is made between the insulating outer shell and a reference ground.

For the reporting, there are two potential free changeover contacts available. The device is integrated in a plastic housing that is made for the mounting on top-hat railways.

The voltage between a cable sheath and the earth is measured by a rectifier. If the voltage limit is exceeded a signalling relay is addressed.

The circuit operates with the constant-current principle. This means that even after the voltage increases to more than 1000 V the demand for electricity is not increasing. The leakage current flowing to earth is dimensioned with only 2 mA. Only in cases of failure the current load will be increased to 6 mA. The state of switching is displayed locally by a signal lamp.

For further information please download the datasheet: