Cable Fault Location . . . Not for the Faint of Heart (Part III)

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Obtaining an approximate location of a fault prior to tracking along the cable path saves time, effort and reduces potential stress to the cable.  Keep in mind that although an approximate location can be obtained a pinpointing technique is still advised. 


Tracking and pinpointing techniques include:

 

Cable Type

Tracking / Pinpointing Techniques

Best Conditions/Limitations

Telecommunication (Copper)

Voltage gradient

 

Ideal for locating and pinpointing ground faults.  Limitation: Best suited for direct buried underground cable.

 

Tone Tracing

Can be used for both locating and pinpointing open circuits and/or ground faults when cables travel in conduit, pipe or trays.  Caution: Low frequency (audio) tones should be used.

 

Low Voltage Signal & Control

Voltage gradient

 

Ideal for locating and pinpointing ground faults.  Limitation: Best suited for direct buried underground cable.

 

Tone Tracing

Can be used for both locating and pinpointing open circuits and/or ground faults when cables travel in conduit, pipe or trays.  Caution: Low frequency (audio) tones should be used.

 

Electric Power (Medium and High Voltage)

Capacitive discharge / surging / “thumping”

Best suited for medium voltage electric power cable.  The capacitive discharge technique is performed with a surge generator.  This device converts line power into high voltage, unidirectional, impulses that are transmitted into a faulted power cable.  The surges create breakdown at the point of the cable fault (fault within the dielectric material of the cable).  The discharge of energy through the fault gap creates an audible “thump” that can be detected on the surface of the ground directly above the flashing cable fault.  Caution: This technique can cause stress to service aged cable and can accelerate the channel growth of “trees” in an aged dielectric.  Care should be taken to minimize the voltage applied to the cable.  Limitation: This technique alone will not locate a solid short in the cable (a spark gap is required to produce the audible “thump”).  In areas of heavy traffic and background noise it is strongly recommended that acoustic listening devices are used.

 

Voltage gradient

 

Ideal for locating and pinpointing ground faults on low voltage cable or locating sheath faults on jacked medium voltage cable.  Limitation: Best suited for direct buried underground cable.

 

 

Tone Tracing

Can be used for both locating and pinpointing open circuits and/or ground faults when cables travel in conduit, pipe or trays. 

 


When faults occur the pressure is on, but keep a cool head and stick to your step-by-step procedures, they will serve you well and keep you on the right path.  Call Protec Equipment Resources, we will be happy to outfit you with state-of-the-art cable testing, fault locating and fault pinpointing equipment as well as share our many years of experience.