CHAPTER XV 

 CABLE TESTING 

 FAULT LOCATION 



Continuity of service is essential to the success of any elec- 

 trical undertaking, whether it be for supplying light or power. 

 So far as the transmission lines are concerned, continuity implies 

 that the risk of interruption has been reduced to a minimum by 

 the use of proper methods of construction, and of suitable 

 materials, such as cables, insulators, etc. Even when the 

 greatest care has been exercised in these matters, cables will 

 break down, line wires will become crossed or grounded and 

 insulators will be punctured or broken. 



Accidents which interrupt the service are often due to abnormal 

 conditions, over which one has no control, and it is necessary 

 to have means of locating the position of the defective parts of 

 the lines or cables, in order that repairs may be expeditiously 

 made. Newly installed power cables not infrequently break 

 down during the high-voltage acceptance tests, and these breaks 

 must be located. 



The special problem of locating faults in long submarine cables 

 is discussed in such works as Kempe's "Handbook of Electrical 

 Testing," and will not be considered here. 



In general, the methods here treated will be those employed 

 in dealing with power cables in cities, and with telephone and 

 telegraph lines, and it will be assumed that only one fault, or 

 connection to ground, exists. 



The theory underlying the methods of fault location is very 

 simple, but, on account of constantly varying circuit conditions, 

 the practical execution of the tests requires a skill and judgment 

 which can be obtained only by actual experience. 



Location of Grounds and Crosses. An earth fault, or ground, 

 is due to any defect in the insulation of the conductor which 

 impairs or destroys its efficiency so that a current may pass 

 from the wire to the earth or to the cable sheath. A cross is due 



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