INTERPRETATION, APPLICATION AND GUIDELINES ON ENFORCEMENT OF 30 CFR
18.22 Boring-Type Machines Equipped for Auxiliary Face
Paragraph 18.22 of 30 CFR Part 18 requires each boring-type continuous-mining machine submitted for approval to be constructed with an unobstructed continuous space(s) of not less than 200 square inches total cross sectional area on or within the machine to which flexible tubing may be attached to facilitate auxiliary face ventilation.
This unobstructed continuous space(s) may consist of two or more spaces, the combined area of which must total a minimum of 200 square inches.
18.26 Static Electricity
The subject section requires nonmetallic rotating parts, such as belts and fans, to be provided with a means to prevent an accumulation of static electricity.
When V-belts are used, V-belts that meet the static conducting criteria specified in the Rubber Manufacturers Association Bulletin No. 3, Edition 2, approved 1972, Power Transmission Belt Technical Bulletin, satisfy this requirement. This criteria requires a resistivity measurement of the new belt to be 6 megohms or less when measured using two 5/8" diameter flat contacts, 8-1/2" apart on centers, moistened with water, and pressed against the belt with a force of 12-1/2 pounds per contact. The measurement shall be with an ohmmeter operating at a potential of 500 volts and having a range from 0 to 10 megohms.
18.30 Windows and Lenses
Paragraph 18.30(b) of 30 CFR Part 18 requires windows or lenses, other than headlight lenses, having an exposed area greater than 8 square inches to be provided with guarding or equivalent.
The exception for headlight lenses is also applicable to lenses of all machine lighting fixtures. Therefore, lenses having an exposed area greater than 8 square inches on machine lighting fixtures are not required to be provided with guarding or equivalent to satisfy the requirements of this paragraph. When installed on a machine, protection from damage must be provided by guarding or location, in accordance with the requirements of Paragraph 18.46(b) of Part 18.
18.32 Fastenings - Additional Requirements
Part 18, 30 CFR, provides construction requirements for explosion-proof enclosures. However, the use of eye bolts in through holes in these enclosures is not specifically addressed. When an eye bolt is installed as a plug in a through hole in an explosion-proof enclosure, it shall be secured by a continuous gas-tight weld (all around). Eye bolts used in through holes in conjunction with other devices where future access to the devices is desired, such as core pins in motor designs, shall be secured by spot welding, brazing, or equivalent.
18.36 Cables Between Machine Components
Clamping of Hose Conduit
Paragraph 18.36(b) of Part 18, 30 CFR, requires cables between machine components to be protected from mechanical damage by position, flame-resistant hose conduit, metal tubing or troughs.
To meet this requirement, when hose conduits are used, they should be clamped to a hose tube, gland extension, or equivalent, at both ends. Clamping the hose conduit directly to the cable is unacceptable.
18.37 Lead Entrances
The subject section specifies requirements for properly packed lead entrances. When the lead entrance is properly packed, a threaded packing nut shall have a minimum of a 3-effective (full) thread engagement with its mating part.
18.40 Cable Clamps and Grips
Section 18.40 of Part 18, 30 CFR, requires installation of insulated clamps or cable grips to prevent strain on both ends of each cable or cord leading from a machine to a detached or separately-mounted component. The requirement for strain relief does not apply to intrinsically safe cables and cords where they enter nonexplosion-proof components.
Cable-grip-type strain relief devices are unacceptable as strain relief devices meeting the requirements of this section in situations where the cable is placed intermittently in tension. Under this condition, the strain relief device may creep along the cable until its use no longer prevents strain on terminals of the cable on which it is installed.
Additionally, each cable exiting a battery enclosure shall be provided with an insulated strain clamp installed to prevent strain on the cable connections at the battery terminals. Cable grips anchored to the cable are unacceptable for this application.
Where the subject strain relief device is acceptable, a section on proper installation is required to be added to the factory inspection form or other appropriate document. The directions should indicate that:
1. Sufficient slack in the cable shall be provided between the machine and the strain relief device.
2. A hose clamp shall be provided on the outby end of the strain relief device to prevent slippage along the cable jacket.
To enable MSHA to verify compliance with the requirements of 30 CFR 18.40, all applicants for approval of a machine or system shall fully identify on submitted documentation each cable clamp or grip used on the machine or system.
The following information shall be provided for insulated strain clamps on submitted or referenced drawings:
1. the flame-resistant insulation material and thickness;
2. the method of securing the clamp to the cable; and
3. the clamp dimensions with tolerances. The clamps shall be designed such that a minimum interference of l/8 inch or 10 percent of the nominal cable outside diameter, whichever is smaller, is provided between the clamp and the minimum cable outside diameter.
If cable grips are used in lieu of insulated strain clamps, the submitted or referenced drawings shall specify:
1. that sufficient slack is provided in the cable between the machine and the strain relief device; and
2. that an integral clamp is provided at the outby end of the cable grip which can be tightened to secure the grip in place after the grip is properly positioned on the cable.
18.41 Plug and Receptacle-Type Connectors
Use of Padlocks on Battery Connectors
Paragraph 18.41(f) of Part 18, 30 CFR, allows for the use of a padlock in lieu of an interlock on connectors used on mobile battery-powered machines, provided the plug is held in place by a threaded ring or equivalent mechanical fastening in addition to the padlock.
An acceptable means for meeting this requirement is the use of a device that is captive and requires a special tool to disengage to allow separation of the connector, along with a caution tag that the connector must not be disengaged under load.
18.45 Cable Reels
Insulation of Cable Reel and Spooling Devices
30 CFR § 18.45(e) requires cable reels and spooling devices to be insulated with flame-resistant material.
To satisfy the intent of this requirement, any part of the machine that the trailing cable normally contacts, such as the cable reel hub and flanges, cable guide, sheaves, and bar rollers, must be insulated to prevent voltage being placed on the machine frame from spot contact with a worn or damaged trailing cable. The insulating material shall be tested and accepted as flame-resistant by the Approval and Certification Center. Cable reel hub and flanges, cable guide, sheaves, and bar rollers may be made or formed from non-metallic flame-resistant insulating materials. Also, these parts may be made of metal provided the surfaces contacted by the cable are coated or lined with a flame- resistant material.
Isolated components, insulated from the machine frame, are acceptable if they are inaccessible to mine personnel while operating the machine. For shuttle cars, isolated components are not permitted in the area between the sheave wheels and the area housing the cable reel and spooling device. They are permitted if the isolated parts are located away from contact by the mine personnel. Since it is normal practice for mine personnel to clean mined material build up on bar rollers, these rollers must be insulated to prevent a damaged trailing cable from energizing the rollers. In this case the bar rollers are not considered isolated.
18.47 Voltage Limitation
The voltage of alternating-current control circuits shall not exceed nominal 120 volts line-to-line. This requirement will allow any appropriate control circuit wiring configuration, including those that allow or cause 120 volt line-to-ground control voltage levels to exist.
18.48 Circuit-Interrupting Devices
Clarification of Terms Used in 30 CFR 18.48
The following terms have been more specifically defined in order to clarify 30 CFR 18.48.
1. Circuit-interrupting device. A circuit-interrupting device is considered to be a single device designed and installed to disconnect all power conductors on a machine from the trailing cable. The device shall simultaneously open all phase conductors on an alternating-current or direct-current machine. The contacts of the device shall be either spring loaded and latched closed or held closed by a magnetic field.
The device shall be:
- a. Installed so that it can be operated (opened and closed) and reset without opening the enclosure in which it is mounted.
b. Designed so that the interruption of all power conductors occurs in a single enclosure.
c. Mounted in a manner so as to preclude the possibility of its closing by gravity.
d. Capable of carrying and interrupting the full-load current of the machine.
2. Power Conductor/Control Conductor. A power conductor is considered to be a conductor that supplies electric power to an electric component or device on a machine or to a related detached component of a machine. This definition includes conductors supplying electric power to motors, motor controllers, power resistors, power take-off receptacles, power transformers and lighting components (e.g., transformers, resistors, ballasts and fixtures).
Conductors not covered by this definition include:
a. The trailing cable conductors.
b. The conductors that supply electric power to control transformers provided that the control transformers are located in the same enclosure as the main circuit-interrupting device.
c. Control circuit conductors.
d. Conductors that supply electric power to a machine mounted methane monitoring system(s).
Note: The voltage of alternating-current control circuits shall not exceed 60 volt to ground.
Control circuit conductors are considered to be conductors used for control circuits and for connections between instrument transformer secondaries, instruments, meters, relays, or other similar equipment.
A motor controller is considered to be a device or group of devices that serves to govern, in some predetermined manner, the electric power delivered to the motor or group of motors of which it is connected.
3. Trailing Cable Termination. The trailing cable is considered to extend from the last short-circuit protective device which meets the requirements of 30 CFR 75.601 through 30 CFR 75.601-3 to the line side of the circuit interrupting device required by 30 CFR 18.48(a). When a connector or connection box is used to sectionalize the trailing cable on the machine, the portion of cable between the connector and/or connection box and the line side of the circuit interrupting device required by 30 CFR 18.48(a) will be considered to be part of the trailing cable provided the conductors in the on board portion of the trailing cable are not smaller than the minimum acceptable size of the conductors in the off board portion of the trailing cable. In addition, the on board portion of the trailing cable shall be protected in accordance with the requirements of 30 CFR 18.36(b). The on board portion of the trailing cable will not be required to be flame resistant if the cable is installed in flame resistant hose conduit.
When it is impracticable to mount the circuit interrupting device on board the machine as provided in 30 CFR 18.48(b), the trailing cable is considered to extend from the last short-circuit protective device which meets the requirements of 30 CFR 75.601 through 75.601-3 to its first point of connection on the machine.
4. Manually-Operated Controller. A "manually operated controller" as referenced in 30 CFR 18.48(a) is a rotary drum controller such as was used to control the traction motors of mining machine trucks, loaders and continuous mining machines.
These interpretations are based on current regulations and existing technology. It is recognized that these interpretations of 30 CFR, Part 18, could potentially have a significant impact on the design of mining machinery.
Deenergization of Lighting Conductors by Main Circuit-Interrupting Device Paragraph 18.48(a) of Part 18, 30 CFR, requires that each machine be equipped with a circuit-interrupting device by means of which all power conductors can be deenergized at the machine.
Conductors to lighting components are considered power conductors and shall be deenergized by the main circuit-interrupting device.
Two-Pole Switches Required for Lighting Circuits
Paragraph 18.48(c) of Part 18, 30 CFR, requires that "separate two-pole switches shall be provided to deenergize power conductors for headlights or floodlights." These switches must be separate physical devices by which all power conductors for machine lights, headlights, or floodlights can be deenergized; i.e., a switch(s) which controls only the lighting circuit. Relay actuated contactors are not acceptable as the sole means of providing this function.
More than one separate two-pole switch may be used to satisfy this requirement. However, each switch must control only a lighting circuit. All other circuits must be controlled by a different switch(s). Three-phase lighting systems must have a separate three-pole switch to satisfy this requirement. A circuit breaker may be used as the required switch for the lighting circuit.
18.50 Protection Against External Arcs and Sparks
Power Take Off Receptacles
Section 18.50 of Part 18, 30 CFR, requires the frames of components not on a common chassis to be maintained at safe voltages by means of diode grounding, actuation of a circuit interrupting device, or a separate grounding conductor within the input power cable. In order to ensure that the PTO adequately provides means of fulfilling these requirements for any type of auxiliary mining equipment which it may power, each PTO receptacle is required to have an electrode which is separate from those used for power, connected to frame ground.
Grounding of Machine Components
The subject section requires that provisions shall be made for maintaining the frames of all off-track machines and enclosures of related detached components at safe voltages.
All metallic enclosures used on an electrical machine are required to have a common electrical ground with the frame of the machine by either the method of attachment or by use of a separate grounding conductor.
To improve the safety afforded by permissible products, effective May 1, 1980, the Approval and Certification Center in applying Part 18 requires:
1. The cross-sectional area of the grounding conductor shall be at least 50 percent of one of the power conductors on No. 6 (AWG) or larger cables, and cables smaller than No. 6 (AWG) shall be required to have a grounding conductor at least the same size as one power conductor. This requirement eliminates the exception previously permitted concerning the use of a ground fault tripping relay.
2. In addition, all machine-mounted lighting fixtures shall be electrically grounded to the machine by a separate grounding conductor.
Grounding Through Cable Reels
Paragraph 18.50(a) of Part 18, 30 CFR, provides for maintaining the frames of off-track machines and the enclosures of related detached components at safe voltages by use of a separate conductor(s) by which the frame or enclosure can be connected to an acceptable grounding medium.
In order to satisfy the requirements of this paragraph, alternating current cable reels shall have at least one slip ring that will be used solely for the grounding circuit.
Acceptance of Silicon Diodes for Grounding
Paragraph 18.50(c) of Part 18, 30 CFR, contains provisions for acceptance of silicon diodes for maintaining the frames of off-track machines and the enclosures of related detached components at safe voltages.
The requirements contained in this paragraph are consistent with, but not as explicit as, the requirements of Paragraphs 75.703-3(d)(1) through 75.703-3(d)(10) of Part 75, 30 CFR. Therefore, the installation and rating of silicon diodes shall be consistent with the requirements for Part 75, 30 CFR, to satisfy the provisions of Paragraph 18.50(c) of Part 18, 30 CFR. The installation of silicon diodes shall meet the following minimum requirements:
1. Installation of silicon diodes shall be restricted to electric equipment receiving power from a direct-current system with one polarity grounded;
2. Where such diodes are used on circuits having a nominal voltage rating of 250, they must have a forward current rating of 400 amperes or more, and have a peak inverse voltage rating of 400 or more;
3. Where such diodes are used on circuits having a nominal voltage rating of 550, they must have a forward current rating of 250 amperes or more, and have a peak inverse voltage rating of 800 or more;
4. Where fuses approved by the Secretary are used at the outby end of a trailing cable connected to electrical equipment employing silicon diodes, the rating of such fuses must not exceed 150 percent of the nominal current rating of the grounding diodes;
5. Where circuit breakers are used at the outby end of a trailing cable connected to electrical equipment employing silicon diodes, the instantaneous trip setting shall not exceed 300 percent of the nominal current rating of the grounding diode;
6. Overcurrent devices must be used and installed in such a manner that the operating coil circuit of the main contactor will open when a fault current with a value of 25 percent or less of the diode rating flows through the diode;
7. The silicon diode installed must be suitable to the grounded polarity of the power system in which it is used and its threaded base must be solidly connected to the machine frame on which it is installed;
8. In addition to the grounding diode, a polarizing diode must be installed in the machine control circuit to prevent operation of the machine when the polarity of a trailing cable is reversed;
9. When installed on permissible equipment, all grounding diodes, overcurrent devices, and polarizing diodes must be placed in explosion-proof compartments;
10. When grounding diodes are installed on a continuous miner, their nominal diode current rating must be at least 750 amperes or more.
Additionally, assemblies of multiple diodes combined to provide the required voltage and current ratings are acceptable in lieu of a single diode having the required ratings.
18.51 Electrical Protection of Circuits and Equipment
Circuit-Interrupting Device; External Operation Requirement
A circuit-interrupting device may be accepted without a method for external operation if the following criteria are met:
1. the circuit-interrupting device is not required by 30 CFR 18.51(a);
2. the circuit-interrupting device protects only control circuit wire(s) or device(s);
3. the circuit-interrupting device provides protection only for cables or components internal to the explosion-proof enclosure; and
4. the circuit-interrupting device can be reclosed without exposing personnel to any energized power circuit.
18.52 Renewal of Fuses
Criteria for Suitable Interlock Systems
The following criteria shall be applied to determine a suitable interlock system as required by 30 CFR, Part 18, Section 18.52: 1. The interruption of the electrical circuit must be accomplished in an explosion proof enclosure.
2. The electrical circuit will not automatically reenergize when the explosion proof integrity is reestablished.
Silicon Controlled Rectifier (SCR) Fuses
When Silicon Controlled Rectifier fuses are used, the following interpretation applies:
1. Fuses used to protect SCR's are power fuses and therefore, the enclosure housing them shall meet 30 CFR Section 18.52 interlock requirements.
2. A microswitch circuit may be used to satisfy the interlock requirements of Section 18.52 provided that the electrical circuit will not automatically reenergize when the explosion proof integrity of the enclosure is reestablished.