30 C.F.R. Subpart I—Underground High-Voltage Distribution
Title 30 - Mineral Resources
[Statutory Provisions] High-voltage circuits entering the underground area of any coal mine shall be protected by suitable circuit breakers of adequate interrupting capacity which are properly tested and maintained as prescribed by the Secretary. Such breakers shall be equipped with devices to provide protection against under-voltage grounded phase, short circuit, and overcurrent. Circuit breakers protecting high-voltage circuits entering an underground area of any coal mine shall be located on the surface and in no case installed either underground or within a drift. The following circuit schemes will be regarded as providing the necessary protection to the circuits required by §75.800: (a) Ground check relays may be used for undervoltage protection if the relay coils are designed to trip the circuit breaker when line voltage decreases to 40 percent to 60 percent of the nominal line voltage; (b) Ground trip relays on resistance grounded systems will be acceptable as grounded phase protection; (c) One circuit breaker may be used to protect two or more branch circuits, if the circuit breaker is adjusted to afford overcurrent protection for the smallest conductor. (a) Circuit breakers and their auxiliary devices protecting underground high-voltage circuits shall be tested and examined at least once each month by a person qualified as provided in §75.153; (b) Tests shall include: (1) Breaking continuity of the ground check conductor, where ground check monitoring is used; and (2) Actuating at least two (2) of the auxiliary protective relays. (c) Examination shall include visual observation of all components of the circuit breaker and its auxiliary devices, and such repairs or adjustments as are indicated by such tests and examinations shall be carried out immediately. (a) Recordkeeping. The operator shall make a record of each test, examination, repair, or adjustment of all circuit breakers protecting high-voltage circuits which enter any underground area of the mine. (b) Record security. These records shall be made in a secure book that is not susceptible to alteration or electronically in a computer system so as to be secure and not susceptible to alteration. (c) Retention and access. These records shall be retained at a surface location at the mine for at least one year and shall be made available to authorized representatives of the Secretary, the representative of miners, and other interested persons. [64 FR 43287, Aug. 10, 1999] [Statutory Provisions] The grounding resistor, where required, shall be of the proper ohmic value to limit the voltage drop in the grounding circuit external to the resistor to not more than 100 volts under fault conditions. The grounding resistor shall be rated for maximum fault current continuously and insulated from ground for a voltage equal to the phase-to-phase voltage of the system. (a) Except as provided in paragraph (b) of this section, high-voltage circuits extending underground and supplying portable, mobile, or, stationary high-voltage equipment shall contain either a direct or derived neutral which shall be grounded through a suitable resistor at the source transformers, and a grounding circuit, originating at the grounded side of the grounding resistor, shall extend along with the power conductors and serve as a grounding conductor for the frames of all high-voltage equipment supplied power from that circuit. (b) Notwithstanding the requirements of paragraph (a) of this section, the Secretary or his authorized representative may permit ungrounded high-voltage circuits to be extended underground to feed stationary electric equipment if: (1) Such circuits are either steel armored or installed in grounded, rigid steel conduit throughout their entire length; or, (2) The voltage of such circuits is nominally 2,400 volts or less phase-to-phase and the cables used in such circuits are equipped with metallic shields around each power conductor, and contain one or more ground conductors having a total cross sectional area of not less than one-half the power conductor; and, (3) Upon a finding by the Secretary or his authorized representative that the use of the circuits described in paragraphs (b) (1) and (2) of this section does not pose a hazard to the miners. (c) Within 100 feet of the point on the surface where high-voltage circuits enter the underground portion of the mine, disconnecting devices shall be installed and so equipped or designed in such a manner that it can be determined by visual observation that the power is disconnected, except that the Secretary or his authorized representative may permit such devices to be installed at a greater distance from such area of the mine if he determines, based on existing physical conditions, that such installation will be more accessible at a greater distance and will not pose any hazard to the miners. [38 FR 4975, Feb. 23, 1973] [Statutory Provisions] On and after September 30, 1970, high-voltage, resistance grounded systems shall include a fail safe ground check circuit to monitor continuously the grounding circuit to assure continuity and the fail safe ground check circuit shall cause the circuit breaker to open when either the ground or pilot check wire is broken, or other no less effective device approved by the Secretary or his authorized representative to assure such continuity, except that an extension of time, not in excess of 12 months, may be permitted by the Secretary on a mine-by-mine basis if he determines that such equipment is not available. The maximum voltage used for ground check circuits under §75.803 shall not exceed 96 volts. Ground check systems not employing pilot check wires will be approved only if it is determined that the system includes a fail safe design causing the circuit breaker to open when ground continuity is broken. (a) Underground high-voltage cables used in resistance grounded systems shall be equipped with metallic shields around each power conductor with one or more ground conductors having a total cross sectional area of not less than one-half the power conductor, and with an insulated external conductor not smaller than No. 8 (A.W.G.) or an insulated internal ground check conductor not smaller than No. 10 (A.W.G.) for the ground continuity check circuit. (b) All such cables shall be adequate for the intended current and voltage. Splices made in such cables shall provide continuity of all components. [38 FR 4976, Feb. 23, 1973] [Statutory Provisions] Couplers that are used with medium-voltage or high-voltage power circuits shall be of the three-phase type with a full metallic shell, except that the Secretary may permit, under such guidelines as he may prescribe, no less effective couplers constructed of materials other than metal. Couplers shall be adequate for the voltage and current expected. All exposed metal on the metallic couplers shall be grounded to the ground conductor in the cable. The coupler shall be constructed so that the ground check continuity conductor shall be broken first and the ground conductors shall be broken last when the coupler is being uncoupled. [Statutory Provisions] Single-phase loads, such as transformer primaries, shall be connected phase-to-phase. [Statutory Provisions] All underground high-voltage transmission cables shall be installed only in regularly inspected air courses and haulageways, and shall be covered, buried, or placed so as to afford protection against damage, guarded where men regularly work or pass under them unless they are 6 [Statutory Provisions] Disconnecting devices shall be installed at the beginning of branch lines in high-voltage circuits and equipped or designed in such a manner that it can be determined by visual observation that the circuit is deenergized when the switches are open. [Statutory Provisions] Circuit breakers and disconnecting switches underground shall be marked for identification. [Statutory Provisions] In the case of high-voltage cables used as trailing cables, temporary splices shall not be used and all permanent splices shall be made in accordance with §75.604. Terminations and splices in all other high-voltage cables shall be made in accordance with the manufacturer's specifications. [Statutory Provisions] Frames, supporting structures and enclosures of stationary, portable, or mobile underground high-voltage equipment and all high-voltage equipment supplying power to such equipment receiving power from resistance grounded systems shall be effectively grounded to the high-voltage ground. [Statutory Provisions] Power centers and portable transformers shall be deenergized before they are moved from one location to another, except that, when equipment powered by sources other than such centers or transformers is not available, the Secretary may permit such centers and transformers to be moved while energized, if he determines that another equivalent or greater hazard may otherwise be created, and if they are moved under the supervision of a qualified person, and if such centers and transformers are examined prior to such movement by such person and found to be grounded by methods approved by an authorized representative of the Secretary and otherwise protected from hazards to the miner. A record shall be kept of such examinations. High-voltage cables, other than trailing cables, shall not be moved or handled at any time while energized, except that, when such centers and transformers are moved while energized as permitted under this section, energized high-voltage cables attached to such centers and transformers may be moved only by a qualified person and the operator of such mine shall require that such person wear approved and tested insulated wireman's gloves. [35 FR 17890, Nov. 20, 1970, as amended at 60 FR 33723, June 29, 1995] A person who meets the requirements of §75.153 is a qualified person within the meaning of §75.812. The operator shall maintain a record of all examinations conducted in accordance with §75.812. Such record shall be kept in a book approved by the Secretary. Source: 67 FR 11001, Mar. 11, 2002, unless otherwise noted.
Sections 75.814 through 75.822 of this part are electrical safety standards that apply to high-voltage longwall circuits and equipment. All other existing standards in 30 CFR must also apply to these longwall circuits and equipment where appropriate. (a) High-voltage circuits must be protected against short circuits, overloads, ground faults, and undervoltages by circuit-interrupting devices of adequate interrupting capacity as follows: (1) Current settings of short-circuit protective devices must not exceed the setting specified in approval documentation, or seventy-five percent of the minimum available phase-to-phase short-circuit current, whichever is less. (2) Time-delay settings of short-circuit protective devices used to protect any cable extending from the section power center to a motor-starter enclosure must not exceed the settings specified in approval documentation, or 0.25-second, whichever is less. Time delay settings of short-circuit protective devices used to protect motor and shearer circuits must not exceed the settings specified in approval documentation, or 3 cycles, whichever is less. (3) Ground-fault currents must be limited by a neutral grounding resistor to not more than— (i) 6.5 amperes when the nominal voltage of the power circuit is 2,400 volts or less; or (ii) 3.75 amperes when the nominal voltage of the power circuit exceeds 2,400 volts. (4) High-voltage circuits extending from the section power center must be provided with— (i) Ground-fault protection set to cause deenergization at not more than 40 percent of the current rating of the neutral grounding resistor; (ii) A backup ground-fault detection device to cause deenergization when a ground fault occurs with the neutral grounding resistor open; and (iii) Thermal protection for the grounding resistor that will deenergize the longwall power center if the resistor is subjected to a sustained ground fault. The thermal protection must operate at either 50 percent of the maximum temperature rise of the grounding resistor, or 150 °C (302 °F), whichever is less, and must open the ground-wire monitor circuit for the high-voltage circuit supplying the section power center. The thermal protection must not be dependent upon control power and may consist of a current transformer and overcurrent relay. (5) High-voltage motor and shearer circuits must be provided with instantaneous ground-fault protection set at not more than 0.125-ampere. (6) Time-delay settings of ground-fault protective devices used to provide coordination with the instantaneous ground-fault protection of motor and shearer circuits must not exceed 0.25-second. (7) Undervoltage protection must be provided by a device which operates on loss of voltage to cause and maintain the interruption of power to a circuit to prevent automatic restarting of the equipment. (b) Current transformers used for the ground-fault protection specified in paragraphs (a)(4)(i) and (5) of this section must be single window-type and must be installed to encircle all three phase conductors. Equipment safety grounding conductors must not pass through or be connected in series with ground-fault current transformers. (c) Each ground-fault current device specified in paragraphs (a)(4)(i) and (5) of this section must be provided with a test circuit that will inject a primary current of 50 percent or less of the current rating of the grounding resistor through the current transformer and cause each corresponding circuit-interrupting device to open. (d) Circuit-interrupting devices must not reclose automatically. (e) Where two or more high-voltage cables are used to supply power to a common bus in a high-voltage enclosure, each cable must be provided with ground-wire monitoring. The ground-wire monitoring circuits must cause deenergization of each cable when either the ground-monitor or grounding conductor(s) of any cable become severed or open. On or after May 10, 2002, parallel connected cables on newly installed longwalls must be protected as follows: (1) When one circuit-interrupting device is used to protect parallel connected cables, the circuit-interrupting device must be electrically interlocked with the cables so that the device will open when any cable is disconnected; or (2) When two or more parallel circuit-interrupting devices are used to protect parallel connected cables, the circuit-interrupting devices must be mechanically and electrically interlocked. Mechanical interlocking must cause all devices to open simultaneously and electrical interlocking must cause all devices to open when any cable is disconnected. (a) The section power center must be equipped with a main disconnecting device installed to deenergize all cables extending to longwall equipment when the device is in the “open” position. See Figures I-1 and I-2 in Appendix A to this subpart I. (b) Disconnecting devices for motor-starter enclosures must be maintained in accordance with the approval requirements of paragraph (f) of §18.53 of part 18 of this chapter. The compartment for the disconnect device must be provided with a caution label to warn miners against entering the compartment before deenergizing the incoming high-voltage circuits to the compartment. (c) Disconnecting devices must be rated for the maximum phase-to-phase voltage of the circuit in which they are installed, and for the full-load current of the circuit that is supplied power through the device. (d) Each disconnecting device must be designed and installed so that— (1) Visual observation determines that the contacts are open without removing any cover; (2) All load power conductors can be grounded when the device is in the “open” position; and (3) The device can be locked in the “open” position. (e) Disconnecting devices, except those installed in explosion-proof enclosures, must be capable of interrupting the full-load current of the circuit or designed and installed to cause the current to be interrupted automatically prior to the opening of the contacts of the device. Disconnecting devices installed in explosion-proof enclosures must be maintained in accordance with the approval requirements of paragraph (f)(2)(iv) of §18.53 of part 18 of this chapter. (a) High-voltage cables must be guarded at the following locations: (1) Where persons regularly work or travel over or under the cables. (2) Where the cables leave cable handling or support systems to extend to electric components. (b) Guarding must minimize the possibility of miners contacting the cables and protect the cables from damage. The guarding must be made of grounded metal or nonconductive flame-resistant material. Longwall mining equipment must be provided with cable-handling and support systems that are constructed, installed and maintained to minimize the possibility of miners contacting the cables and to protect the high-voltage cables from damage. (a) Energized high-voltage cables must not be handled except when motor or shearer cables need to be trained. When cables need to be trained, high-voltage insulated gloves, mitts, hooks, tongs, slings, aprons, or other personal protective equipment capable of providing protection against shock hazard must be used to prevent direct contact with the cable. (b) High-voltage insulated gloves, sleeves, and other insulated personal protective equipment must— (1) Have a voltage rating of at least Class 1 (7,500 volts) that meets or exceeds ASTM F496–97, “Standard Specification for In-Service Care of Insulating Gloves and Sleeves” (1997). (2) Be examined before each use for visible signs of damage; (3) Be removed from the underground area of the mine or destroyed when damaged or defective; and (4) Be electrically tested every 6 months in accordance with publication ASTM F496–97. ASTM F496–97 (Standard Specification for In-Service Care of Insulating Gloves and Sleeves, 1997) is incorporated by reference and may be inspected at any MSHA Coal Mine Safety and Health district office, or at MSHA's Office of Standards, Regulations, and Variances, 1100 Wilson Blvd., Room 2352, Arlington, Virginia 22209–3939, and at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, call 202–741–6030, or go to: http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.php. In addition, copies of the document can be purchased from the American Society for Testing and Materials, 100 Barr Harbor Drive, West Conshohocken, Pennsylvania 19428–2959. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. [67 FR 11001, Mar. 11, 2002, as amended at 67 FR 38386, June 4, 2002; 71 FR 16668, Apr. 3, 2006] Compartment separation and cover interlock switches for motor-starter enclosures must be maintained in accordance with the approval requirements of paragraphs (a) and (b) of §18.53 of part 18 of this chapter. (a) Electrical work on all circuits and equipment associated with high-voltage longwalls must be performed only by persons qualified under §75.153 to perform electrical work on all circuits and equipment. (b) Prior to performing electrical work, except for troubleshooting and testing of energized circuits and equipment as provided for in paragraph (d) of this section, a qualified person must do the following: (1) Deenergize the circuit or equipment with a circuit-interrupting device. (2) Open the circuit disconnecting device. On high-voltage circuits, ground the power conductors until work on the circuit is completed. (3) Lock out the disconnecting device with a padlock. When more than one qualified person is performing work, each person must install an individual padlock. (4) Tag the disconnecting device to identify each person working and the circuit or equipment on which work is being performed. (c) Each padlock and tag must be removed only by the person who installed them, except that, if that person is unavailable at the mine, the lock and tag may be removed by a person authorized by the operator, provided— (1) The authorized person is qualified under paragraph (a) of this section; and (2) The operator ensures that the person who installed the lock and tag is aware of the removal before that person resumes work on the affected circuit or equipment. (d) Troubleshooting and testing of energized circuits must be performed only— (1) On low- and medium-voltage circuits; (2) When the purpose of troubleshooting and testing is to determine voltages and currents; and (3) By persons qualified to perform electrical work and who wear protective gloves on circuits that exceed 40 volts in accordance with the following table: (4) Rubber insulating gloves must be rated at least for the nominal voltage of the circuit when the voltage of the circuit exceeds 120 volts nominal and is not intrinsically safe. (e) Before troubleshooting and testing a low- or medium-voltage circuit contained in a compartment with a high-voltage circuit, the high-voltage circuit must be deenergized, disconnected, grounded, locked out and tagged in accordance with paragraph (b) of this section. (f) Prior to the installation or removal of conveyor belt structure, high-voltage cables extending from the section power center to longwall equipment and located in the belt entries must be: (1) Deenergized; or (2) Guarded in accordance with §75.816 of this part, at the location where the belt structure is being installed or removed; or (3) Located at least 6.5 feet above the mine floor. (a) At least once every 7 days, a person qualified in accordance with §75.153 to perform electrical work on all circuits and equipment must test and examine each unit of high-voltage longwall equipment and circuits to determine that electrical protection, equipment grounding, permissibility, cable insulation, and control devices are being properly maintained to prevent fire, electrical shock, ignition, or operational hazards from existing on the equipment. Tests must include activating the ground-fault test circuit as required by §75.814(c). (b) Each ground-wire monitor and associated circuits must be examined and tested at least once each 30 days to verify proper operation and that it will cause the corresponding circuit-interrupting device to open. (c) When examinations or tests of equipment reveal a fire, electrical shock, ignition, or operational hazard, the equipment must be removed from service immediately or repaired immediately. (d) At the completion of examinations and tests required by this section, the person who makes the examinations and tests must certify by signature and date that they have been conducted. A record must be made of any unsafe condition found and any corrective action taken. Certifications and records must be kept for at least one year and must be made available for inspection by authorized representatives of the Secretary and representatives of miners. In addition to the high-voltage cable design specifications in §75.804 of this part, high-voltage cables for use on longwalls may be a type SHD cable with a center ground-check conductor no smaller than a No. 16 AWG stranded conductor. The cables must be MSHA accepted as flame-resistant under part 18 or approved under subpart K of part 7. [67 FR 11001, Mar. 11, 2002; 67 FR 18823, Apr. 17, 2002]
Title 30: Mineral Resources
PART 75—MANDATORY SAFETY STANDARDS—UNDERGROUND COAL MINES
Subpart I—Underground High-Voltage Distribution
§ 75.800 High-voltage circuits; circuit breakers.
§ 75.800-1 Circuit breakers; location.
§ 75.800-2 Approved circuit schemes.
§ 75.800-3 Testing, examination and maintenance of circuit breakers; procedures.
§ 75.800-4 Testing, examination, and maintenance of circuit breakers; record.
§ 75.801 Grounding resistors.
§ 75.802 Protection of high-voltage circuits extending underground.
§ 75.803 Fail safe ground check circuits on high-voltage resistance grounded systems.
§ 75.803-1 Maximum voltage ground check circuits.
§ 75.803-2 Ground check systems not employing pilot check wires; approval by the Secretary.
§ 75.804 Underground high-voltage cables.
§ 75.805 Couplers.
§ 75.806 Connection of single-phase loads.
§ 75.807 Installation of high-voltage transmission cables.
§ 75.808 Disconnecting devices.
§ 75.809 Identification of circuit breakers and disconnecting switches.
§ 75.810 High-voltage trailing cables; splices.
§ 75.811 High-voltage underground equipment; grounding.
§ 75.812 Movement of high-voltage power centers and portable transformers; permit.
§ 75.812-1 Qualified person.
§ 75.812-2 High-voltage power centers and transformers; record of examination.
High-Voltage Longwalls
§ 75.813 High-voltage longwalls; scope.
§ 75.814 Electrical protection.
§ 75.815 Disconnect devices.
§ 75.816 Guarding of cables.
§ 75.817 Cable handling and support systems.
§ 75.818 Use of insulated cable handling equipment.
§ 75.819 Motor-starter enclosures; barriers and interlocks.
§ 75.820 Electrical work; troubleshooting and testing.
------------------------------------------------------------------------ Circuit voltage Type of glove required------------------------------------------------------------------------Greater than 120 volts (nominal) (not Rubber insulating gloves intrinsically safe). with leather protectors.40 volts to 120 volts (nominal) (both Either rubber insulating intrinsically safe and non-intrinsically gloves with leather safe). protectors or dry work gloves.Greater than 120 volts (nominal) Either rubber insulating (intrinsically safe). gloves with leather protectors or dry work gloves.------------------------------------------------------------------------
§ 75.821 Testing, examination and maintenance.
§ 75.822 Underground high-voltage longwall cables.
Appendix A to Subpart I to Part 75—Diagrams of Inby and Outby Switching
