U.S. Department of Labor Mine Safety and Health Administration Protecting Miners' Safety and Health Since 1978

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30 CFR § 75.601-1 Short circuit protection; ratings and settings of circuit breakers. Circuit breakers providing short circuit protection for trailing cables shall be set so as not to exceed the maximum allowable instantaneous settings specified in this section; however, higher settings may be permitted by an authorized representative of the Secretary when he has determined that special applications are justified:

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              ---------------------------+-------------------
                                         | Maximum allowable
                                         |  circuit breaker
               Conductor size AWG or MGM |   instantaneous
                                         | setting (amperes)
              ---------------------------+-------------------
               14........................|        50
               12........................|        75
               10........................|       150
               8.........................|       200
               6.........................|       300
               4.........................|       500
               3.........................|       600
               2.........................|       800
               1.........................|     1,000
               1/0.......................|     1,250
               2/0.......................|     1,500
               3/0.......................|     2,000
               4/0.......................|     2,500
               250.......................|     2,500
               300.......................|     2,500
               350.......................|     2,500
               400.......................|     2,500
               450.......................|     2,500
               500.......................|     2,500
              ---------------------------+-------------------