VOLUME V - COAL MINES
75.511 Low-, Medium, or High-Voltage Distribution Circuits and Equipment; Repair
For the purpose of this Section, electrical work is considered to be the work required to install or maintain electric equipment or conductors. Listed below are examples of work that is required to be performed by a qualified person or a person trained to perform electrical work and to maintain electric equipment under the direct supervision of a qualified person.
- Locating faults in cables
- Replacing blown fuses, except blown fuses on trolley poles may be replaced by miners other than persons qualified to do electrical work when:
- it is not necessary to remove a cover lid or panel to gain access to the fuse;
- the correct replacement fuse is available;
- the fuse holder, power conductors, and motor controller have not been damaged;
- warning signs are placed on the equipment to warn miners of the dangers of changing a blown trolley pole fuse without removing the trolley pole;
- information signs are placed on the equipment to inform miners of the correct fuse for the equipment; and
- the miners who install the fuses have received training in the hazards of energized trolley wires, voltage and current ratings of fuses, and in the safe methods for installing fuses. All miners who perform tasks involving equipment that use trolley fuses (e.g., motorman, supply crewman) should receive this training as part of the training they receive under applicable provisions of Part 48.
- Making splices, connections and terminations in electric conductors and cables
- Installation of couplers on the end of cables
- Repair of electric components of electrically-powered portable, mobile or stationary equipment
- Installation of electric wiring
- Electrical maintenance of permissible equipment
- Any type of work performed inside rooms, vaults, substations and other similar enclosures where energized parts or conductors are exposed
- Any type of work performed inside transformers, power centers, rectifiers, switch boxes, switch houses, panels and other enclosures of electric equipment or conductors
- Electrical troubleshooting and testing
- Handling energized high-voltage power cables (see Section 75.812)
Listed below are examples of work that is not required to be performed by a qualified person or by a person trained to perform electrical work and maintain electric equipment under the direct supervision of a qualified person:
- operation of electric equipment;
- normal operation of control switches, switch boxes, or circuit breakers, provided no energized parts or conductors are exposed;
- operation of cutout switches in trolley circuits;
- hanging or removing fuse nips on or from trolley wires;
- changing bits;
- handling energized trailing cables;
- inserting low- and medium-voltage cable couplers into receptacles or withdrawing low- and medium-voltage cable couplers from receptacles;
- transportation of electric equipment and cables;
- mechanical repairs on electrically-powered equipment, provided no energized parts or conductors are exposed;
- installation and repair of equipment and circuits in which shock hazards do not exist (having a nominal rating of 40 volts or less), provided such equipment is not required to be permissible; and
- installation, repair, and guarding of trolley wires and trolley feeder wires.
Section 75.510 states that energized trolley wires may be repaired only by a person trained to perform electrical work and to maintain electrical equipment. Repair work is not required to be performed by a qualified person but must be performed by a person trained to repair and maintain energized trolley wires. However, electrical work, such as connecting a feeder wire inside the enclosed housing of a rectifier, is required to be performed by a qualified person or by a person trained to perform electrical work and to maintain electrical equipment under the direct supervision of a qualified person.
The phrase "under the direct supervision of a qualified person"must, as a minimum, include the following:
- The qualified person shall examine and/or test an electric circuit or machine and determine the need for repair or maintenance;
- The qualified person must give specific instructions to the employee assigned to perform this work with respect to the nature and extent of the repairs to be performed and, where necessary, prescribe the manner in which the work is to be performed;
- The qualified person is, at all times, under continuing duty to instruct, advise, or consult with the employee in the event the work which he has assigned cannot be performed by the employee in the manner prescribed; and
- The qualified person must examine and test, if necessary, the completed work before the circuit is energized or the machine is returned to service.
Testing and troubleshooting of energized equipment shall be done only by qualified persons, except that a person trained to perform electrical work and to maintain electrical equipment under the direct supervision of a qualified person may do testing and troubleshooting on energized circuits as a part of his or her training program if a qualified person is present at all times to observe, instruct, and aid the trainee during such testing and troubleshooting.
Mining equipment manufacturers' service representatives are not required to be qualified persons, but are considered to be persons "trained to perform electrical work and to maintain electrical equipment under the direct supervision of a qualified person." When work is performed by manufacturers' service representatives who are not qualified persons, the completed work is required to be examined and tested, if necessary, by a qualified person before the machine or equipment is placed in service.
Rebuilding of electric equipment by original equipment manufacturers or rebuild shops may be performed by persons other than qualified persons; however, mine management is under a continuing responsibility to assure that such equipment is examined by a qualified person to assure safe operating condition before the equipment is placed in service.
Section 75.512 requires examinations and tests to be made only by a qualified person. The very nature of the required examinations and tests precludes the work being performed by a person trained to perform electrical work and to maintain electrical equipment under the direct supervision of a qualified person.
The disconnecting device is intended to provide workers with a visible means of readily determining that the equipment or circuit is deenergized. The worker must be able to see the power disconnect blades or contacts easily to determine, without any doubt, that the circuit is deenergized.
Disconnecting devices shall be locked out, where possible, and suitably tagged by persons who perform the work. Locking out is"possible" in almost all cases and can be accomplished in a practical manner. Single-pole blade-type disconnects and fused-type disconnects in high-voltage circuits are examples of cases where locking out is not practically possible. In all instances,trailing cables equipped with cable couplers or fused nips shall be opened, tagged and locked out. Some methods by which locking out may be accomplished are:
- Drilling a small hole in the shell of the cable coupling so as to accommodate a padlock;
- Chaining the cable coupler to the power center with a short cable and padlock; and
- Placing the cable couplers or fuse nips inside a box equipped with a padlock.
In every instance, the padlock shall be removed by the person who installed it if the person is present in the mine. If the person who installed the padlock is not present, the operator or the operator's agent (a responsible official) must designate a person to remove the padlock.
"Suitably tagged" means that a sign with wording such as "Danger,Repairs in Progress," shall be attached to the locked disconnecting device.
Disconnecting Devices Installed On-Board Mine EquipmentWhen disconnecting devices are installed on-board mine equipment,they may be used to meet the requirements of 30 CFR 75.509,75.511 and 75.1725(c), provided the disconnecting devices are safety constructed, designed, and installed on the equipment as required by 30 CFR 75.520.
To meet the requirements of 30 CFR 75.509, 75.511, and 75.1725(c), disconnecting devices must function so as to provide positive visual confirmation that the equipment or circuit is deenergized. The worker must be able to easily see the power disconnect blades or contacts to determine, without any doubt,that the equipment or circuit is deenergized.
To meet the requirements of 30 CFR 75.520, disconnecting device enclosures must be explosion-proof and installed in a location on the machine that will not be hazardous to the machine operator or diminish visibility. In addition, the enclosure housing the disconnecting device must be the first enclosure on-board the machine that the trailing cable enters. The covers of disconnecting device enclosures must be provided with interlock switches so that miners cannot be exposed to energized parts when these covers are removed.
These covers must also be provided with caution labels to warn miners against entering these enclosures before deenergizing the trailing cables to the equipment. The disconnecting device must be capable of carrying the full-load current of the machine, and of interrupting the full-load current of the machine unless the device is interlocked to remove the load prior to opening. In addition, if the device is intended to interrupt short circuit current, it shall have a current interrupting rating greater than the available fault current at the machine.
Permitting a disconnecting device installed on-board a machine to be used as the visual disconnect for the equipment creates a change in established electrical work procedures. As a result,all miners who perform maintenance on this equipment must receive task training as required by 30 CFR 48.7(a)(3). This training must include clear instructions that the disconnecting device will only deenergize the machine, and that the trailing cable will remain energized.
75.512 Electric Equipment; Examination, Testing and maintenance
This Section requires that each individual piece of electric equipment, including locomotives, personnel carriers, electric track switches and derails, compressors, car hauls, conveyor units, pumps, rock-dusting machines, battery-powered equipment and permissible equipment, be examined and tested. The required examinations and tests must be thorough enough to insure that the electric equipment has not deteriorated through neglect, abuse or normal use into an unsafe condition that could result in a shock,fire, or other hazard to the miners.
The record of examinations of electric equipment required by this Section shall list separately each individual piece of electric equipment in the mine.
If the qualified person making the required examinations and test finds any potentially dangerous condition, that person shall immediately cause the defective equipment to be removed from service until such condition is corrected.
If each individual piece of electric equipment is not listed separately and identified with a serial or company number and the location of each unit, and if all dangerous conditions and corrective actions are not recorded, the records of weekly examinations of electric equipment are incomplete and shall be considered to be in violation of this Section.
The qualified person making the examination is not required to sign the book; however, the name of the qualified person who made the required examination and test shall appear under "Examiner"in the book, Form 6-1492 (Weekly Record). The results of examinations required by this Section may be entered or recorded by the qualified person making the examination or by a responsible mine official (superintendent, mine foreman,electrical or maintenance foreman) or may transfer information from a check list, filled out by the examiner, to the required book. If the examiner cannot be readily identified from the records of weekly examinations of electric equipment, the records are incomplete and in violation of this Section.
75.512-2 Frequency of Examinations
The examination of electric equipment may be made at any time during each calendar week, even if more than 7 days pass between examinations.
75.513-1 Electric Conductors; Size
If power cables are manufactured in accordance with the Insulated cable Engineers Association (ICEA) standards, the ampacity tables by the ICEA shall be used for determining compliance with this Section.
75.514 Electrical Connections or Splices; Suitability
This Section requires that conductors be joined together with clamps, connectors, track bonds, or other suitable connectors to provide good electrical connections. Splices made by twisting conductors together or by tying knots in conductors, splices that have bare or exposed conductors, or splices that heat or arc under load shall constitute noncompliance.
When splices are made in insulated conductors, the conductors must be reinsulated with insulating materials similar to the original. Flame-resistant insulating material should be used to replace flame-resistant insulation. Glass, asbestos, or other heat-resistant material should be used to replace high temperature insulation.
Feeder wires shall be joined together by proper feeder-wire splices. Wire rope clamps will be acceptable for splicing feeder wire; however, a minimum of two clamps of the proper size should be used in making each splice. The wire rope clamps should be examined periodically for tightness.
Where track is used as a power conductor, efficient connections require that:
- Both rails of main-line tracks shall be welded or bonded at every joint, and cross bonds shall be installed at intervals of not more than 200 feet. If the rails are paralleled with a feeder circuit of like polarity, such parallel feeder shall be bonded to the track rails at intervals of not more than 1,000 feet.
- At least one rail on secondary track-haulage rails shall be welded or bonded at every joint, and cross bonds shall be installed at intervals of not more than 200 feet.
- Track switches in entries shall be well bonded.
- In rooms where electric equipment is dependent upon the room track rails as a power conductor, rail joints shall be secured by means of fish plates, angle bars, or the equivalent, and at least one rail shall be bonded at each joint.
Main-line track is interpreted to be track used to transport coal outby the junction of two or more coal-producing sections. All other track is considered to be secondary track and includes track that is used to transport miners and material or coal from a single coal-producing section. Both rails of secondary track may need to be bonded or welded at each joint if the additional current-carrying capacity is needed for compliance with Section 75.1001.
Bonding as used herein means a connection used to insure the required electrical conductivity between the rails. The connection may be obtained mechanically, as with a wedge or by welding the bonds on the rails.
75.515 Cable Fittings; Suitability
This Section requires fittings of such design as to prevent chafing of cable or wire insulation that would expose or accidentally ground the conductors at points where they enter the compartment walls of switch boxes, starters, motors, cable couplers, etc. Insulated wires passing through walls of metal enclosures shall be protected against damage to the insulation by insulated bushings or suitable insulating material, such as fire-resistant hose conduit used in conjunction with a suitable fitting or clamp that will prevent movement of the conductor in the opening. Fittings for cables need not be insulated. When insulated wires pass through holes in metal dividers within the same enclosure, insulating bushings or other suitable insulating material shall be used to bush the holes. For the purpose of this Section, "cable" means two or more insulated conductors covered by an additional abrasion-resistant covering.
75.516 Power Wires; Support
"Power wire" means a current-carrying conductor which may be bare, insulated, or part of a cable assembly.
Shielded cables that meet all of the requirements of Section 75.804 are not required to be installed on insulators, even if they are used to supply low-, medium-, or high-voltage equipment.All other power wires and cables supplying belt conveyor drives,pumps, air compressors, and other units of portable or stationary equipment (except distribution boxes, portable pumps, battery chargers, and rock-dusting machines which are used on coal-producing sections and which require frequent movement) shall be installed on insulators and are not allowed to contact combustible material, roof, or ribs.
Acceptable insulators are constructed of noncombustible,nonabsorptive insulating material adequate for the voltage being used. Furthermore, insulators must have sufficient mechanical strength and must be installed in such a manner as to provide adequate support for the power wires or cables installed on them.Cables that meet the requirements of Section 75.600 may be supported from noncombustible material such as sand rock or slate roof, concrete or metal roof supports, or masonry walls by lengths of flame-resistant cable or conveyor belting.
Trolley wires and trolley feeder wires shall be supported only on bell-and-clip-type insulated hangers or other supports especially designed for that purpose.
All wires and cables that are required to be supported on insulators shall be supported in such manner that they do not contact combustible materials, roof, or ribs.
75.516-1 Installed Insulators
J-hooks shall be acceptable as insulators for the permanent installation of insulated cables if the manufacturer certifies the dielectric and tensile strength of the J-hook and if, in the opinion of the authorized representative of the Secretary, the J-hook is adequate for the duty imposed. The following guidelines shall be used as criteria for the acceptance of J-hooks as insulators:
- The dielectric strength of the J-hook shall not be less than eight times the voltage of the circuit.
- The tensile strength shall not be less than three times the weight the J-hook is intended to support.
This Section does not prohibit single-conductor cables used in three-phase resistance-grounded low-voltage circuits from being installed on proper hangers and supported by a grounded messenger wire or insulated wires from being installed in grounded metal conduit.
75.517 Power Wires and Cables; Insulation and Protection
Any ungrounded power conductor extending from the track entry for any purpose shall be insulated. In addition, power wires and cables shall be installed under well supported roof and far enough away any from moving equipment to prevent damage; however,in some locations, metal or nonmetallic conduit may be necessary for additional protection against damage. Examples of these locations include: where power wires or cables other than trolley feeder wires cross the trolley wire; where power wires or cables pass through doors or stoppings; where power wires or cables are installed along supply storage areas; where power wires or cables are installed on tight corners with insufficient clearance; or other areas where power wires or cables cannot be isolated sufficiently to afford protection.
This Section also requires that damaged insulation on insulated power wires and cables (including trailing cables) and damaged jackets on power cables (including trailing cables) be repaired.
The outer jacket of a cable is intended to protect the internal conductors from cuts, abrasion, moisture, etc., and must be intact for the cable to be fully protected as required by this Section.
Tapes or other materials that are used to form the outer jacket of approved permanent splices may be used to replace damaged areas of outer jackets of trailing cable. Outer jackets shall be replaced in such manner so as to prevent moisture from entering the cable.
Tar-impregnated friction tape is not adequate for insulation or protection in the damp and wet areas of underground coal mines.Such tape will absorb mine water, which is highly conductive,creating a serious shock hazard to the miners.
75.518-1 Electric Equipment and Circuits; Overload and Short Circuit Protection; Minimum Requirements
In direct-current systems that are either ungrounded or provided with a neutral grounding point, protective elements shall be provided for both positive and negative lines. This necessitates the use of either a two-pole circuit breaker or a fuse in each polarity. Fuses of the correct type and capacity are acceptable as overload protection only for d.c. or single-phase a.c.circuits and motors. The proper selection is based on wire size,motor design, horsepower, and method of starting. If the computed value is other than a common size, the next higher size common fuse or thermal element is acceptable.
The installation of overload devices on locomotives operating on grades exceeding 5 percent can create a hazardous condition due to a decrease in braking power if the overcurrent protective devices open. Noncompliance with this Section shall not be cited for locomotives operating on grades exceeding 5 percent until suitable automatic brakes have been designed and installed on such locomotives and haulage cars.
75.518-2 Incandescent Lamps, Overload, and Short-Circuit Protection
Not more than 8 feet in distance means not more than 8 feet of ungrounded conductor.
75.519-1 Main Power Circuits; Disconnecting Switches;Locations
This Section applies to low- and medium-voltage power circuits entering a mine and to low-, medium-, and high-voltage power circuits at the bottom of shafts and boreholes. The requirements for disconnecting switches for high-voltage power circuits entering a mine are contained in Section 75.802(c).
A high-voltage cable coupler, switch, or other device not designed for load-breaking duty that is located at the bottom of a shaft or borehole may be used in conjunction with a high-voltage circuit breaker located on the surface provided:
- A remote control switch that, when activated, will open the circuit breaker is provided at the bottom of the shaft or borehole; and
- A visual or audible means to indicate that the circuit breaker has opened when the remote control switch is activated is provided at the bottom of the shaft or borehole. Signal lights will be acceptable if the lights receive power through the auxiliary contacts on the circuit breaker.