Program Policy Manual - VOLUME V - Mine Safety and Health ...

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MSHA PROGRAM POLICY MANUAL VOLUME V setting of d.c. overload relay located in the output leads of the rectifier bridge. In such instances, the instantaneous setting of the circuit breaker shall not exceed 82 percent of the equivalent d.c. overload relay setting. Reclosing circuit breakers used to protect trolley systems should be equipped with load-measuring circuits. Reclosing circuit breakers used to protect multiple-feed systems should also be equipped with voltage-differential circuits. Loadmeasuring and voltage-differential circuits are necessary to prevent the circuit breaker from reclosing on a short circuit or abnormally high load. Load-measuring circuits should be adjusted to as low a value of current as practical. In almost all instances, the system will perform satisfactorily with the load-measuring circuits adjusted at or below 300 amperes; however, there may be instances when slightly higher values are required because of pumps, lights, and other continuous loads on the system. Voltage-differential circuits should be adjusted to values equal to or exceeding 85 percent of the system voltage. The mine operator should establish a program under which all trolley circuits will be tested and calibrated at least once every 6 months. The circuit breaker may be tested by loading the circuit until the current reaches that amount necessary to cause actuation of the circuit breaker or an external current source may be used. Circuit breakers equipped with solid state controls that are actuated by the voltage drop across a shunt may be tested by disconnecting the control circuit leads from the shunt and applying the proper amount of voltage to the shunt leads to cause actuation. Current actuated relays shall be tested by passing the necessary amount of current through them to cause actuation. Relays that have a current calibration coil may be calibrated with an external current calibration source, provided that: (1) each relay is installed, adjusted, maintained, tested and calibrated in accordance with the manufacturer's instructions; and (2) the tolerance of the calibration current source and the specified relay operating tolerance shall not exceed 15 percent. The record required by this Section shall be kept in a book and should contain the following: 1. Date of test; 2. Name of qualified person making test; 3. Indicated current setting; and February 2003 (Release V-33) 87
MSHA PROGRAM POLICY MANUAL VOLUME V 4. Current required to activate the breaker. 75.1002-1 Location of Other Electric Equipment; Requirements for Permissibility The distance shall be measured by following the shortest distance that air can travel (tight string distance) through crosscuts, entries or other openings. In longwall mining, the 150-foot distance shall be measured in a straight line from the wire, cable or electric equipment in question to the outby edge of the longwall roof-support system. Except in longwall mining, the 150-foot distance specified in this Section and Section 75.1002 shall be measured from the wire, cable or electric equipment in question to the nearer of either: 1. The outby edge of the pillar being mined; or 2. The inby edge of the solid pillars immediately outby the previously pillared area. 75.1003 Insulation of Trolley Wires, Trolley Feeder Wires and Bare Signal Wires; Guarding of Trolley Wires and Trolley Feeder Wires Guarding shall be done with wood, plastic, or other substantial nonconductive material, firmly secured. Guarding shall extend for at least 6 feet from each side of the door or stopping. In advancing sections where the trolley feeder wire is extended beyond the track, or in retreating sections where the track is removed before the trolley or trolley feeder wires, adequate guarding shall be required between the end of such wires and the end of the tracks. 75.1003-1 Other Requirements for Guarding of Trolley Wires and Trolley Feeder Wires "Equipment" for the purpose of this Section is interpreted to mean track-mounted equipment, off-track mining equipment, component parts of mining equipment, mine supplies, or any item used in the operation or maintenance of a coal mine. This Section applies to movement of any item that is used in the production or transportation of coal or in performing any duty necessary for the operation and maintenance of the mine. This Section requires mine management to take adequate precautions prior to movement of equipment to prevent the item being moved from contacting the trolley or trolley feeder wire. If the February 2003 (Release V-33) 88
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