Cable Theft Monitoring Device

Brief Description of the Cable Theft Monitor Operation

The Cable Theft Monitor (Better known as the CTM) can monitor single or 3 phase cables with a maximum voltage of 600V AC

The controller has 2 Outputs which get wired to the Inputs. The first output will indicate a power failure on the cable we are monitoring, and the second output indicates that the cable has been cut.

The controller is normally in a “sleep mode” while AC power is present on the cable it is monitoring and  will only start up when the AC power is no longer present on the line, this lack of AC presence could be due to a number of reasons:

  1. The load (e.g. pump) has been turned off
  2. The load (e.g. pump) has been removed for maintenance.
  3. Mains Utility Power has failed
  4. Thieves have cut the cable while it was live, this cut has caused an imbalance and the circuit breaker upstream has tripped because of this event.

Once the AC power is no longer present on the cable then the controller will wake up”, two things will then happen simultaneously, a) the Power Fail Output will go active & b) The CTM will inject a small DC signal into the cable.

At the far end of the cable you will have a device called the DC Reflector installed, this device allows the DC signal we are injecting to be reflected and returned to our controller. If the cable has been cut then the DC signal will not return to the controller and the Cable Cut Output will go active

It is important to note that the controller should be installed after the circuit breaker that feeds the load at the far end.

The same logic would apply for the DC Reflector, if the load has a circuit breaker installed then the DC Reflector should be installed before this circuit breaker. The reason for this is simple, if either of these circuit breakers trip for any reason then the controller will start injecting the DC signal and it will not be reflected due to the open path created by the circuit breaker. This open path will result in a false alarm as the DC signal will fail to return

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