Instantaneous Circuit Breaker Settings for the Short-Circuit Protection of Direct Current 300-and 600-V Trailing Cables

Present Federal regulations which specify maximum instantaneous circuit breaker settings for the short-circuit protection of coal mine trailing cables are discussed. Characteristics of mine power systems, which limit short-circuit current in dc trailing cables, and minimum expected short-circuit currents for dc 300- and 600-V trailing cables are analyzed. New maximum instantaneous circuit breaker settings, based on minimum expected short-circuit currents and typical circuit breaker tolerances, are proposed with emphasis on safety, and tests are cited.