Burn-Off Characteristics of A-C. Low-Voltage Network Cables

This paper describes tests made to determine the characteristics of the clearance of faults in several types of a-c. low-voltage network copper-conductor cables installed in accordance with present standards of underground construction, and includes a discussion of test results together with other relative data studied. The investigation included the burning clear of various types of faults in buried non-magnetic sheath cables, and non-metallic sheath and lead-covered cables for duct installation. A comparison is made of the burn-off characteristics of the several cable constructions and their installations. The amount of short-circuit current and length of time required to clear the different types of faults in No. 4/0, 350,000-and 500,000-cir. mil cables have been determined by test and by calculations in some instances. Conclusive data were not obtained to clear up all present conflicting opinions related to the burn-off characteristics of a-c. low-voltage network cables. However, a study of the subject matter would seem to establish at least a partial basis in regard to burn-off characteristics for determining the conductor size of low-voltage network mains and the spacing of network transformers. Desirable developments for a-c. network cables indicated by the results of this investigation are emphasized.