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

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MSHA PROGRAM POLICY MANUAL VOLUME V 75.605 Clamping of Trailing Cables to Equipment Section 18.40 requires insulated strain clamps or cable grips on the trailing cables of permissible machines, except that mesh-wire cable grips (e.g. Kellems grips) are not permitted on trailing cable reels. Where mesh-wire cable grips are permitted, they shall be installed in accordance with the following: 1. Sufficient slack shall be provided in the trailing cable between the machine and the cable grip. 2. A hose clamp shall be provided on the outby end of the cable grip to prevent slippage along the cable jacket. A length of flame-resistant hose conduit is acceptable for insulating a metal strain clamp. 75.606 Protection of Trailing Cables Trailing cables shall be placed away from roadways and haulageways where they might be run over or damaged by mobile equipment. Where the method of mining requires that trailing cables cross roadways or haulageways, the cables shall be securely supported from the mine roof, or if the height of the coal seam does not permit hanging the cables, the cables shall be installed in a trench cut into the mine roof or mine floor. A substantial bridge for the equipment to pass over the cables is also acceptable if, in the opinion of the inspector, the cables are adequately protected. February 2003 (Release V-33) 71
MSHA PROGRAM POLICY MANUAL VOLUME V Subpart H Grounding 75.701 Grounding Metallic Frames, Casings, and Other Enclosures of Electric Equipment When a three-phase resistance grounded system supplies power to a rectifier bridge and to other portable or mobile loads, neither the positive nor negative conductor of the direct-current circuit can be grounded. The frames of the direct-current equipment must be grounded to the alternating-current ground rectifier frame. However, when a power system is being designed so as to provide a separate bank of transformers to supply power to the rectifier bridge and a separate bank of transformers to supply power to the a.c. portable or mobile loads, then one polarity of the rectifier bridge can be grounded. All frames of direct-current equipment are then grounded to the grounded power conductor. 75.702 Protection Other Than Grounding Portable tools protected by an approved system of double insulation, or its equivalent, need not be grounded. Where such an approved system is employed, the tool will be distinctly marked. 75.703 Grounding Off-Track Direct-Current Machines and Enclosures of Related Detached Components "Related detached components" refers to associated parts such as contactor compartments, control switches, or rheostats that are not installed on the frame of the machine. The metal frames or enclosures of such components shall be connected to the same grounding medium as the main frame of the machine to which it is related. Metal frames or housings of pumps, battery chargers, sequence and slippage switches, breaker boxes, remote control switches, rheostats, rock-dusting machines, auxiliary fans, belt drives, belt feeders, contactor compartments, and any other equipment or devices receiving power from direct-current power systems shall be grounded to the grounding medium of the power system feeding such equipment or devices. The grounding medium for d.c. systems is normally the mine track or grounded d.c. feeder. When ungrounded d.c. systems are used, the grounding medium is usually the grounded frame of the rectifier or generator. The metal battery case of batteries being charged shall be grounded. In instances where batteries are being charged without removing them from mobile equipment, the frame of the machine or battery case shall be grounded to the grounded frame of the charger to prevent the machine from becoming "alive" through failure of insulation in the charger, such as between primary and February 2003 (Release V-33) 72
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