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

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MSHA PROGRAM POLICY MANUAL VOLUME V 2. Second grounding circuit shall connect the frames of the stationary equipment to a low resistance ground field located near the utilization location. 3. The resistance of the grounding resistor and the resistance of the ground field shall be maintained in such a manner that not more than 100 volts will appear between the equipment frame and earth under fault conditions in the event that the grounding conductor should be severed. 75.803-2 Ground Check Systems not Employing Pilot Check Wires; Approval by the Secretary Wireless ground check circuits shall not be approved unless such circuits are tested and evaluated by Technical Support. 75.804 Underground High-Voltage Cables This Section does not apply to cables of ungrounded high-voltage circuits that are enclosed in steel armor or rigid steel conduit. All high-voltage cables, whether single or multiple conductor, shall conform to this Section. If single-conductor high-voltage cables are used, the cables should be installed on a well-supported messenger wire or on cable hangers, and a power grounding conductor and ground check conductor shall extend along with the power conductors. The messenger wire, when paralleled with the cable shielding, can serve as the grounding conductor for the circuit if the impedance of the grounding circuit is low enough to limit the voltage drop to 100 volts or less. Normally, the high resistance of steel messenger wire will limit the distance the circuit can be extended. The shielding shall be connected to the messenger wire at each splice (single-conductor cables) and, at each termination. Inspectors must calculate the parallel resistance of the messenger wire and the three shields when determining compliance with the requirement for a maximum voltage drop of 100 volts. Cables in systems using "other no less effective device approved by the Secretary or his authorized representative" as provided for in Section 75.803 for assuring grounding circuit continuity are exempted from the requirement to have an insulated ground check conductor. 75.805 Couplers An existing high-voltage coupler that is not equipped with a pin for the ground check circuit may be used if a locking switch is mounted on the coupler so that it cannot be uncoupled until the key is inserted in the lock and the switch is opened. This operation breaks the ground check conductor first. Several February 2003 (Release V-33) 79
MSHA PROGRAM POLICY MANUAL VOLUME V equipment companies are manufacturing conversion kits for installation on existing couplers not provided with ground check pins. Cable couplers that are mounted on portable substations are considered to be receptacles and should be grounded to the same grounding medium as the substation enclosure. When these portable substations supply power to underground circuits, the grounding conductor and shielding in the cable should be insulated from the coupler housing, and the metallic housings of both the receptacle and the male part of the metallic frame of the portable substation. The grounding conductor shielding shall be connected to the grounded side of the groundings resistor. 75.807 Installation of High-Voltage Transmission Cables Energized high-voltage cables shall be stored in unused crosscuts or other unused areas away from haulageways or mantrip stations where miners or equipment could contact or damage such cables. 75.808 Disconnecting Devices A "branch line" means a circuit that is formed by connection to an existing high-voltage circuit for the purpose of feeding branch loads. Cable couplers are acceptable as a disconnecting device only when used with an acceptable device such as a circuit breaker or oilfilled fused cutouts that are used to deenergize the circuit before the cable coupler is uncoupled. If a remote switch in the ground check circuit is used to trip a circuit breaker prior to uncoupling the coupler, visible or audible evidence must be provided to indicate that the circuit breaker has opened before the coupler is uncoupled. 75.809 Identification of Circuit Breakers and Disconnecting Switches The identifying markers for circuit breakers and disconnecting switches shall be large enough and shall be located so that they can be readily seen if the circuits need to be deenergized quickly. Either metallic or plastic material may be used for the marker to adequately identify the circuit (e.g., No. 2 Belt Drive, No. 3 Rectifier, 1 Rt. 3 North, etc.). The identifying markers shall leave no doubt as to which circuit or circuits will be deenergized when the switches are pulled. February 2003 (Release V-33) 80
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