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

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MSHA PROGRAM POLICY MANUAL VOLUME V Section 77.503. Enforcement action should not be taken if cables do not meet the specifics of the 1968 NEC ampacity and temperature rating standards, but equal or surpass the minimum level of safety afforded by compliance with the NEC. This enforcement policy will allow the use of newly-designed electric conductors which are not addressed by the 1968 NEC, but which do comply with Section 77.503 and offer equal or greater miner protection. Trailing cables are required to meet the minimum capacity requirements of the Insulated Power Cable Engineers Association (IPCEA) - National Electric Manufacturers Association (NEMA) standards. This policy does not affect MSHA's treatment of trailing cables. 77.504 Electrical Connections or Splices; Suitability This Section requires that splices made in electric conductors be made in a workman-like manner and establish sufficient electrical conductivity so that the joined conductors will not heat or spark under load. Because of the different characteristics of devices, such as pressure terminal or pressure splicing connectors and soldering lugs, they shall be suitable for the material of the conductor and shall be properly installed and used. Conductors of dissimilar metals shall not be intermixed in a terminal or splicing connector where physical contact occurs between dissimilar conductors, unless the device is suitable for the purpose and conditions of use. Materials such as solder, fluxes, inhibitors, and compounds, where employed, shall be suitable for the use and shall be of a type which will not adversely affect the conductors, installation, or equipment. Soldered splices in electric conductors shall be joined with suitable connectors and then soldered. Splices made by twisting conductors together, tying knots in conductors, splices that have bare or exposed conductors, splices that heat or arc under load, or splices in multiple conductor cables that do not have the outer jacket replaced would constitute noncompliance. All connections or splices in insulated conductors shall be reinsulated to at least the same degree of protection as the remainder of the conductor. Tape, such as rubber, glass, asbestos, or plastic will be acceptable as insulation. Friction tape is not an acceptable insulation material, but may be used to provide mechanical protection. 77.505 Cable Fittings; Suitability For the purpose of this Section, a cable, with either single or multiple conductors, is one that has an outer jacket in addition to the insulation provided for each power conductor. An electrical fitting is an accessory such as a clamp or other part of a wiring system that is intended primarily to perform a February 2003 (Release V-33) 177
MSHA PROGRAM POLICY MANUAL VOLUME V mechanical rather than an electrical function. The function of a proper electrical fitting for a cable entering a junction box, electrical panel, termination box, or other electrical enclosure is to prevent a strain on the electrical connections and to prevent chafing or other movement of the cable that might allow an energized electrical conductor to fault to the enclosure frame. Proper fittings would permit box connectors, packing glands, strain insulators, strain clamps, or metal or wood clamps, etc. Electric circuits that are made up of individual insulated wires that enter junction boxes, termination boxes or other electrical enclosures need not have fittings, but must be provided with insulated bushings. 77.506 Electric Equipment and Circuits; Overload and Short- Circuit Protection Section 77.506 requires "automatic circuit-breaking devices or fuses of the correct type and capacity" on electric equipment and circuits to protect against short circuits and overloads. Section 77.506-1 specifies what was considered to be the correct type and capacity for circuit breakers and fuses at the time the standard was enacted. It requires such devices and fuses to meet the minimum requirements of the 1968 NEC. For certain excavation equipment, requiring strict compliance with the terms of the 1968 NEC could prevent the use of circuit protective devices of appropriate type and capacity. Therefore, Section 77.506-1 should not be applied to some equipment which meets the requirements of Section 77.506. Alternating- and direct-current loop (feedback) systems and their controls, which are used on large shovels, draglines and in-mine hoisting installations are normally designed so that their currents are limited to values below those which would cause a harmful overload condition to circuits or motors. These circuits on the equipment specified above comply with Section 77.506, and will not be required to have short-circuit or overload protective devices to comply with the terms of the NEC. 77.507 Electric Equipment; Switches The intent of this Section is to require that all control devices be fully enclosed to prevent exposure of bare wires and energized parts. Improvised starting methods such as plug and receptable devices, trolley taps and trolley wire "stingers" that are used to start or stop electric motors are examples of noncompliance with this provision. 77.508 Lightning Arresters, Ungrounded and Exposed Power Conductors and Telephone Wires Conductors that are provided with a metallic shield or are February 2003 (Release V-33) 178
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Program Policy Manual - VOLUME V - Mine Safety and Health ...

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