Operational characteristics of trailing cable splices

Abstract

Abstmct-The U.S. Bureau of Mines investigated the operational characteristics of spliced portable power cables. This research had a dual purpose: (1) to determine the thermal and mechanical performance of repaired trailing cables and compare them with undamaged cables, and (2) to gauge the impact of longterm localized heating on the insulating and jacketing materials contained in cable splice kits accepted or approved by the Mine Safety and Health Administration. The ranges of splice joint resistance and tensile breaking strength were determined from laboratory measurements. The choice of crimping tools affected the strength of the splice under tension. Thermal profiles of energized spliced cables were constructed, which showed that spliced conductor joints operated 5 to 20 "C hotter than the intact cable at rated currents. Accelerated life tests of thermallyaged samples of splice kit insulation and jacket materials confirmed a deficiency in the thermal rating of the insulating tape. The recommendations in this paper may be utilized to revise splice kit design, splice kit acceptance criteria, and trailing cable loading guidelines. Characterizing the thermal operating limits of spliced trailing cables may help to minimize associated risks from explosions, fires, personnel burns, and shock. minutes, the splice may catch fue or rupture, jeopardizing underground safety and disrupting production. In fact, the largest criminal penalty ever assessed for mine safety violations ($1 million), involved a defective splice that resulted in a fatality [1,2]. If the current-induced temperature rises of damaged or spliced cable sections could be confined to appropriate limits, trailing cable service life would be lengthened. In addition, splice kit materials that are appropriately rated for the application would minimize the risk that such weakened sections pose from explosion, fire, or personnel burns. This paper documents the accomplishments of a research project supporting the U.S. Bureau of Mines (USBM) goal to enhance the safety of the Nation's underground miners. The specific project objectives were: (1) to determine the thermal and mechanical performance of repaired trailing cable samples and compare them with undamaged cables, and (2) to gauge the impact of long-term localized heating on the insulating and jacketing materials contained in cable splice kits accepted or approved by the Mine Safety and Health Administration (MSHA). The results of this work may be useful in revising splice kit design, splice kit acceptance criteria, and trailing cable loading guidelines. BACKGROUND I. INTRODUCTIONThe trailing cables of mobiIe equipment in underground coal mines are abused mechanically as they are pulled and dragged through this abrasive environment, and rarely last a year. During the course of a cable's brief service life, broken or exposed metallic conductors are repaired at the worksite. Restoration typically involves excising the defective cable portion, rejoining the conductors, insulating, and sealing the splice from mo...