Instantaneous Circuit Breaker Settings for the Short-Circuit Protection of Three-Phase 480-, 600-, and 1040-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. The characteristics of mine power systems that limit short-circuit current in three-phase trailing cables are analyzed and minimum expected short-circuit currents for three-phase 480-, 600-, and 1040-V trailing cables are tabulated. New maximum instantaneous circuit breaker settings, based on minimum expected short-circuit currents and typical breaker tolerances, are proposed with emphasis on safety. Finally, atypical mine power systems are discussed and field tests cited.