Contact Resistance and Temperature Rise of Cable Connections in Cable Distribution Cabinets

Abstract

Initiated by a number of fire accidents in the low voltage switchgear in cable distribution cabinets, investigations have been performed to identify the cause of these fires. The results indicate that the cable connection was likely to be the cause of the problems, rather than overheating of the fuse links accommodated in the fuse switch disconnector modules. In the relevant equipment, the cable is connected with a cable clamp tightened with a specified torque. However, it was found that by mechanically stressing the cable (moving the cable in order to connect another phase), the individual strands of the cable conductor might be displaced and the contact pressure reduced. Based on these findings, laboratory testing have been done, investigating how contact resistance and temperature rise of the cable connection might vary with the practical execution. The results seems to indicate that applying a cable lug connection could be a more reliable solution. Finally, measurement of temperature rise of properly installed cable connections in the field are made by applying miniature wireless sensor elements. The findings show that during a relatively mild Norwegian winter (ambient temperatures between -5-5°C) the temperature rise of the cable connection is far below the relevant temperature limits of such contacts set by the IEC 60439-1.