Protection for low and medium voltage AC trailing cables

In 1981 a mining equipment manufacturer approached the Mine Safety and Health Administration with a combination fuse contactor device requesting that it be permitted as a means of protection for low and medium voltage, three phase AC trailing cables. The concept behind the design of the vacuum contactor-fuse device was to use a vacuum contactor to provide protection to a specific current level during abnormal circuit conditions. If fault currents exceeded this level, a current limiting fuse would be used to interrupt the current before the vacuum contractor could open. The authors describe the tests and criteria developed to ensure that the device provided no less protection than a molded case circuit breaker. Details of the laboratory tests are presented. The vacuum circuit breaker meets 30 CFR 75900, 75902 and 75601 in that it provides suitable protection against undervoltage, grounded phase, overcurrent, and short circuits.<>