Blasting circuits.

§ 75.1323 Blasting circuits. (a) Blasting circuits shall be protected from sources of stray electric current. (b) Detonators made by different manufacturers shall not be combined in the same blasting circuit. (c) Detonator leg wires shall be shunted until connected into the blasting circuit. (d) Blasting cables shall be— (1) Well insulated, copper wire of a diameter not smaller than 18-gauge; and (2) Long enough to permit the round to be fired from a safe location that is around at least one corner from the blasting area. (e) Blasting cables shall be shunted until immediately before firing, except when testing for circuit continuity. (f) Wire used between the blasting cable and detonator circuitry shall— (1) Be undamaged; (2) Be well insulated; (3) Have a resistance no greater than 20-gauge copper wire; and (4) Be not more than 30 feet long. (g) Each wire connection in a blasting circuit shall be— (1) Properly spliced; and (2) Separated from other connections in the circuit to prevent accidental contact and arcing. (h) Uninsulated connections in each blasting circuit shall be kept out of water and shall not contact the coal, roof, ribs, or floor. (i) When 20 or fewer boreholes are fired in a round, the blasting circuit shall be wired in a single series. (j) Immediately prior to firing, all blasting circuits shall be tested for continuity and resistance using a blasting galvanometer or other instrument specifically designed for testing blasting circuits. [53 FR 46786, Nov. 18, 1988; 54 FR 27641, June 30, 1989]