The PCM177 pilot cable monitor is an earth continuity relay. It provides earth continuity protection in accordance with AS/NZS 2081 ensuring the earth connection through a trailing/reeling cable is maintained. A pilot cable is connected to earth via a diode, the PCM177 detects open and short circuits between the pilot and earth conductors of the trailing cables. The unit has filtering to remove unwanted inductively or capacitive coupled ac signals. The LEDs indicate power to the unit and the status of the pilot cable (‘HEALTHY’ LED). There are two changeover contacts rated at 8A/250V which are fail-safe. Output contacts de-energise (unHEALTHY) on conditions of:
- Loss of power
- Open circuit of pilot cable
- Loop resistance exceeds set value.
- Pilot cable shorted to earth.
- Leakage resistance to earth is less than 600Ω
There are two basic operating models;
- Local or automatic reset models go into a HEALTHY condition when no fail conditions exist. A stop button can be wired in series with the pilot cable to de-energize relay if necessary. In local mode, the PCM177 will automatically reset after the fault has been cleared.
- Remote start or latching models have a remote 100Ω series resistor connected across a remotely mounted normally open start button. When start is pressed the PCM177 checks loop resistance before switching to a HEALTHY condition. The PCM177 will go into an unHEALTHY state if the start button is held or stuck for longer than 15 seconds. In latching mode, a manual reset (press start button) is needed after the fault has been cleared.
