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

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MSHA PROGRAM POLICY MANUAL VOLUME V jacketed by a grounded metal covering or enclosure, suspended by a grounded messenger wire, installed under grounded metal framework, protected by the umbrella-effect of overhead grounded static line, or are buried in the earth are not considered exposed for the length so protected. If the trolley wire of a d.c. system is paralleled by an exposed feeder cable, one lightning arrester would provide protection for both if they are interconnected near the lightning arrester. To comply with this Section, three-phase alternating-current circuits should be provided either with three separate lightning arresters or with a three-phase arrester which consists of three arresters in one case having a common ground terminal. 77.511 Danger Signs at Electrical Installations "Major electrical installations" shall include the following: 1. All high-voltage installations housing exposed energized parts, such as: fence enclosed substations; skid-mounted transformers; transformers or switchgear located in vaults or rooms; circuit breaker and switch houses; enclosures on board machines, in preparation plants, or shops, that house high-voltage switches, fuses or exposed buss; and high-voltage motor controls. Examples of high-voltage installations that are not considered to be major are: high-voltage cables serving surface mine equipment; pole-mounted transformers, regulators and capacitors; pole-mounted disconnecting switches; motor generator sets having no exposed highvoltage parts, and high-voltage cables or wiring in conduits passing through enclosures from floor to floor in preparation plants or machines. 2. Rooms or areas housing switchboards containing exposed parts energized at more than 40 volts to ground. 77.513 Insulating Mats at Power Switches Insulating mats or dry wooden platforms are required to be kept in place where a person would normally stand at switchboards or power control switches only if a shock hazard exists. Installations where a shock hazard exists include, but are not limited, to the following: 1. all live front switchboards with exposed components energized at more than 40 volts to ground; and February 2003 (Release V-33) 179
MSHA PROGRAM POLICY MANUAL VOLUME V 2. all overhead high-voltage disconnect switches which are operated from the ground by means of mechanical linkage. (See Section 77.704-9 for requirements for high-voltage switches.) Enclosed power control switches such as portable circuit breakers of switch houses that are supplied power from a resistance-grounded system, as required by Section 77.802 or 77.901, are not considered to pose a shock hazard. Grounded metal mats or plates may not be used instead of insulating mats in front of live front switchboards. Insulating mats or platforms installed at high-voltage installations shall be rated for not less than the phase-tophase voltage of the circuit. Insulating mats can provide such additional safety if placed at low-voltage linestarters, fuse boxes, and other low-voltage switchgear containing renewable parts. 77.516 Electric Wiring and Equipment; Installation and Maintenance Section 77.516 requires, in addition to compliance with Sections 77.503 and 77.506, that electric equipment installed after June 30, 1971, meet the requirements of the NEC. The NEC has been incorporated into MSHA standards to address wiring and wiring methods for surface facilities and structures not specifically covered in Part 77. The NEC will continue to be applied to surface facilities and structures other than the specified excavation equipment. The NEC contains safety guidelines which are not specifically tailored to surface mine excavation equipment and conductors, but which cover a much broader scope. While Section 77.516 addresses wiring and electric equipment installed after June 30, 1971, on surface mining machines, many provisions of the NEC are not applicable to the wiring methods, types of equipment, and conditions on these machines. For example, certain excavation equipment designed and installed since June 30, 1971, is not compatible with the requirements of the 1968 NEC. Therefore, strict application of and compliance with the NEC for the wiring methods used on surface mine excavation equipment is not practicable. Wiring and electric equipment installed after June 30, 1971, on-board electric or diesel-powered surface excavation equipment are not required to comply with the NEC under Section 77.516, although mine operators are free to rely on it as a guideline. This policy applies to equipment such as draglines, shovels, dozers, bucket wheel excavators, mobile February 2003 (Release V-33) 180
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Program Policy Manual - VOLUME V - Mine Safety and Health ...

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