High-Voltage Continuous Mining Machine Standard for Underground Coal Mines, 17529-17553 [2010-7309]

Agencies

• DEPARTMENT OF LABOR
• Mine Safety and Health Administration

[Federal Register Volume 75, Number 65 (Tuesday, April 6, 2010)]
[Rules and Regulations]
[Pages 17529-17553]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2010-7309]


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DEPARTMENT OF LABOR

Mine Safety and Health Administration

30 CFR Parts 18 and 75

RIN 1219-AB34


High-Voltage Continuous Mining Machine Standard for Underground 
Coal Mines

AGENCY: Mine Safety and Health Administration, Labor.

ACTION: Final rule.

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SUMMARY: This final rule revises the Mine Safety and Health 
Administration's (MSHA's) electrical safety standards for the 
installation, use, and maintenance of high-voltage continuous mining 
machines in underground coal mines. It also revises MSHA's design 
requirements for approval of these mining machines. The final rule will 
allow mine operators to use high-voltage continuous mining machines 
with enhanced safety protection against fires, explosions, and shock 
hazards and will facilitate the use of advanced equipment designs.

DATES: The final rule is effective on June 7, 2010. The incorporation 
by reference in this rule is approved by the Director of the Federal 
Register as of June 7, 2010.

FOR FURTHER INFORMATION CONTACT: Patricia W. Silvey, Director, Office 
of Standards, Regulations, and Variances, MSHA, 1100 Wilson Boulevard, 
Room 2350, Arlington, Virginia 22209-3939. Ms. Silvey can be reached at 
silvey.patricia@dol.gov (e-mail), 202-693-9440 (voice), or 202-693-9441 
(facsimile). (These are not toll-free numbers.)

SUPPLEMENTARY INFORMATION: The outline of this final rule is as 
follows:

I. Introduction
    A. Background
    B. Petition for Modification (PFM) Requirements in the Final 
Rule
II. Discussion of the Final Rule
    A. General Discussion--Part 18--Electric Motor-Driven Mine 
Equipment and Accessories
    B. General Discussion--Part 75--Mandatory Safety Standards--
Underground Coal Mines
III. Section-by-Section Analysis
    A. Part 18--Electric Motor-Driven Mine Equipment and Accessories
    B. Part 75--Mandatory Safety Standards--Underground Coal Mines
IV. Executive Order 12866: Regulatory Planning and Review
    A. Population at Risk
    B. Benefits
    C. Compliance Costs
V. Feasibility
    A. Technological Feasibility
    B. Economic Feasibility
VI. Regulatory Flexibility Act (RFA) and Small Business Regulatory 
Enforcement Fairness Act (SBREFA)
    A. Definition of a Small Mine
    B. Factual Basis for Certification
VII. Paperwork Reduction Act of 1995
    A. Elimination of Burden Hours
    B. Annual Burden Hours
    C. Details
VIII. Other Regulatory Considerations
    A. The Unfunded Mandates Reform Act of 1995
    B. Executive Order 13132: Federalism
    C. The Treasury and General Government Appropriations Act of 
1999: Assessment of Federal Regulations and Policies on Families
    D. Executive Order 12630: Government Actions and Interference 
With Constitutionally Protected Property Rights
    E. Executive Order 12988: Civil Justice Reform
    F. Executive Order 13045: Protection of Children From 
Environmental Health Risks and Safety Risks
    G. Executive Order 13175: Consultation and Coordination With 
Indian Tribal Governments
    H. Executive Order 13211: Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution, or Use

[[Page 17530]]

I. Introduction

A. Background

    Horsepower for electrical equipment in mines has increased over the 
years. The voltages required to operate this equipment have also 
increased to accommodate the design of safe, practical, and efficient 
equipment. Because of the industry's need for higher voltages and the 
marked improvement in the design and manufacturing technology of high-
voltage components, MSHA has established requirements for use of high-
voltage electrical equipment such as longwall systems. This rule 
establishes additional requirements to address the use and approval of 
high-voltage continuous mining machines. These additional requirements 
preserve safety and health protections for miners.
    MSHA's existing standards do not allow the use of high-voltage 
continuous mining machines because high-voltage mining machines were 
not available when the standards were developed. MSHA has granted 52 
Petitions for Modification (PFMs) since 1997 to allow mine operators to 
use this equipment. In granting the PFMs, MSHA determined that the 
methods the mine operator proposed to follow when using the high-
voltage equipment would at all times guarantee no less than the same 
measure of protection afforded the miners by the existing standards.
    On July 16, 2004, MSHA published a proposal (69 FR 42812) to 
establish design requirements in part 18 for approval of high-voltage 
continuous mining machines operating in production areas of underground 
mines. The proposal also included new requirements in part 75 for the 
installation, use, and maintenance of high-voltage continuous mining 
machines in underground coal mines.
    In the proposal, MSHA announced that it would hold four public 
hearings in September 2004, and would allow comments through October 
14, 2004. However, on August 23, 2004, MSHA published a notice changing 
the public hearing dates to November 2004 and extending the comment 
period to December 10, 2004 (69 FR 51787). Based on the review of all 
comments and testimony, MSHA re-proposed provisions related to the 
types of trailing cables that could be used with high-voltage 
continuous mining machines and the types of cable handling equipment 
that must be used when handling energized high-voltage trailing cables 
(71 FR 15359, March 28, 2006). In developing the final rule, MSHA 
considered the comments, hearing testimony, and granted PFMs.

B. Petition for Modification Requirements in the Final Rule

    The final rule includes most of the requirements that were in the 
granted PFMs. In each instance where a PFM requirement was not included 
in the rule, MSHA has addressed the Agency's rationale in the section-
by-section analysis of the preamble.
    This final rule supersedes all PFMs granted prior to the effective 
date, and eliminates the need for mine operators to file for a PFM to 
use high-voltage continuous mining machines with voltage up to 2,400 
volts.

II. Discussion of the Final Rule

A. General Discussion--Part 18--Electric Motor-Driven Mine Equipment 
and Accessories

    The final rule addresses design requirements for approval of high-
voltage continuous mining machines. The rule is intended to prevent the 
following hazards:
    (1) High-voltage arcing;
    (2) Ignition of a methane-air mixture surrounding the machine if an 
arc or methane explosion occurs within the explosion-proof enclosure;
    (3) Enclosure failure from an increased pressure rise if an arc or 
methane explosion occurs within the explosion-proof enclosure; and
    (4) Electrical shock hazards to miners when working with or around 
high-voltage equipment.
    One commenter stated that the proposal did not provide the same 
level of safety that some of the granted PFMs provided. This commenter 
expressed concern that MSHA was trying to issue a one-size-fits-all 
regulation while mine-specific PFMs better assure safety. MSHA does not 
believe that the final rule represents a generic approach or 
compromises safety. MSHA reviewed all provisions contained in granted 
PFMs and the final rule includes most of the provisions. However, in 
some cases, the Agency revised the language in the PFMs to allow more 
flexibility for mine specific conditions. The Agency explained at the 
public hearing that Part 18 covers this commenter's examples and should 
eliminate the concerns. Additionally, the final rule incorporates 
additional safety measures such as short-circuit, under-voltage, 
sensitive ground-fault protection, a look-ahead circuit, cable handling 
methods, and cable inspection procedures that would assure the same 
level of safety as the granted PFMs.
    This final rule provides a mining environment as safe as the 
existing environment and facilitates the use of advanced equipment 
designs.

B. General Discussion--Part 75--Mandatory Safety Standards--Underground 
Coal Mines

    This final rule revises 30 CFR Part 75 to establish mandatory 
electrical safety standards for the proper installation of high-voltage 
continuous mining machines, electrical and mechanical protection of the 
equipment, handling of trailing cables, and procedures for performing 
electrical work. These safety standards include new provisions as well 
as most of the provisions contained in granted PFMs.
    There are 27 high-voltage continuous mining machines used in 8 
underground coal mines that have been granted PFMs. Some of the 
requirements in this final rule are not included in those PFMs. 
Accordingly, mine operators with granted PFMs who wish to continue 
using high-voltage continuous mining machines will be required to 
comply with the additional requirements specified in this final rule. 
These additional requirements include new testing and recordkeeping 
requirements for tramming the machine in and out of the mine. In 
addition, there may be other new provisions that mine operators must 
adopt, such as following the cable manufacturers' recommended 
procedures when pulling the trailing cable with equipment other than 
the continuous mining machine (See Sec.  75.828).
    The final rule also revises Sec.  75.1002 by adding paragraph 
(b)(5) to allow the use of high-voltage continuous mining machines in 
areas where permissible equipment is required.

III. Section-by-Section Analysis

A. Part 18--Electric Motor-Driven Mine Equipment and Accessories

Section 18.54 High-Voltage Continuous Mining Machines
    Final Sec.  18.54(a) is derived from existing requirements for 
high-voltage longwall mining systems and is similar to the proposal. 
The final rule retains the proposed requirement that low- and medium-
voltage circuits in each motor-starter enclosure be separated from 
high-voltage circuits by barriers, partitions, or covers. The purpose 
of this provision is to protect persons from coming in contact with 
energized high-voltage conductors or parts when testing and 
troubleshooting low- and medium-voltage circuits.
    Several commenters expressed concern over this proposal. They 
indicated that in order to comply with the proposed provisions, 
existing high-voltage continuous mining machines would need to be 
retrofitted with

[[Page 17531]]

additional interlocked barriers and partitions to separate low- and 
medium-voltage from high-voltage components and circuits. One commenter 
stated that it is not the location of components that is the risk, but 
rather the access to energized high-voltage components. The commenter 
further stated that barriers, partitions, or the enclosure itself can 
prevent access. The primary purpose of proposed paragraph (a) is to 
prevent access to energized high-voltage components and circuits. In 
the final rule, MSHA has revised the proposal to clarify its intent to 
assure that existing equipment would not need retrofitting. The final 
rule permits high-voltage and low- and medium-voltage components and 
circuits in the same compartments if barriers are provided and covers 
are arranged so that testing and troubleshooting can be performed 
without exposing persons to any high-voltage conductors or parts. This 
change allows for flexibility in design and does not reduce safety for 
miners.
    Final paragraph (a), like the proposal, requires barriers and 
partitions to be constructed of grounded metal or nonconductive 
insulating board.
    One commenter expressed a preference for using barriers made of 
insulating boards rather than grounded metal, but stated that either is 
acceptable. MSHA agrees that use of either material would meet the 
requirements of final paragraph (a).
    Final paragraph (b) requires that each removable cover, barrier, or 
partition of a motor-starter enclosure that provides access to high-
voltage components be provided with at least two interlock switches 
that automatically de-energize the high-voltage components when the 
cover, barrier, or partition is removed.
    A commenter expressed concern with the proposed requirement for 
interlock switches on all barriers, partitions, and covers. The 
commenter requested that MSHA not require interlock switches except 
when the cover, barrier, or partition provides access to energized 
high-voltage circuits or parts.
    MSHA did not intend to require interlock switches on all barriers, 
partitions, and covers and has clarified the language in the final rule 
to require interlock switches only when there is direct access to high-
voltage circuits. Interlock switches protect miners from shock hazards 
by de-energizing high-voltage circuits when barriers, partitions, or 
covers are removed.
    Final paragraph (c), like the proposal, requires that circuit-
interrupting devices be designed and installed to prevent automatic re-
closure to protect miners from electrical shocks, fires, explosions, 
and unintentional machine movement. For example, a roof-collapse or 
equipment insulation failure can result in short-circuit or ground-
fault condition. This could result in the automatic re-closing of the 
circuit-interrupting device and pose a hazard to miners. MSHA received 
no comments on this proposal.
    Final paragraph (d), like the proposal, includes requirements for 
the grounding of the electrostatic shield for high-voltage transformers 
supplying control voltages on continuous mining machines.
    Final paragraph (d)(1), like the proposal, requires that the 
nominal control voltage not exceed 120 volts line-to-line. Limiting the 
control voltages to 120 volts line-to-line reduces the potential for 
electrocution of miners. This provision is consistent with granted 
PFMs. MSHA received no comments on this proposal.
    Final paragraph (d)(2), like the proposal, requires that control 
transformers with high-voltage primary windings in each high-voltage 
motor-starter enclosure, or that supply control power to multiple 
motor-starter enclosures, have an electrostatic (Faraday) shield 
installed between the primary and secondary windings. The purpose of 
the electrostatic shield is to isolate the high-voltage from lower-
voltage circuit. This protects miners from high-voltage shocks should a 
fault develop between the primary and secondary windings. Electrostatic 
shielding also prevents transients (sudden short-term changes in 
voltage and current) occurring on the primary circuit from being 
transferred to the secondary circuit. These transients can damage 
equipment and create the risk of a fire and electrical shock.
    Final paragraphs (d)(2)(i) and (d)(2)(ii) address requirements for 
grounding the electrostatic shield. If the transformer has an external 
grounding terminal, paragraph (d)(2)(i) requires the shield to be 
connected from the grounding terminal to the equipment ground by a 
minimum of a No. 12 American Wire Gauge (A.W.G.) grounding conductor. 
This requirement will assure proper current carrying capacity and 
mechanical strength of the grounding conductor.
    If the transformer does not have an external terminal, paragraph 
(d)(2)(ii) requires that the electrostatic shield be connected to the 
transformer frame by an internal conductor. This conductor, generally 
installed when the transformer is manufactured, is considered an 
extension of the shield and therefore may be smaller than a No. 12 
A.W.G. In this case, bolting the transformer frame to the equipment 
enclosure will provide the required path to ground, as long as an 
effective low impedance electrical connection is maintained. MSHA 
received no comments on these proposals.
    Final paragraph (e), like the proposal, addresses requirements for 
indicator light circuits. Final paragraph (e)(1) requires a grounded-
phase indicator light on any ungrounded, three-phase power circuit 
onboard the machine to alert the machine operator when a grounded-phase 
condition occurs. Ungrounded circuits include high-voltage transformers 
that power low- and medium-voltage circuits. The secondary windings of 
these transformers are connected in an ungrounded configuration. With 
ungrounded systems, the capacitive coupling between each phase 
conductor and ground can subject the ungrounded system to dangerous 
over-voltages resulting from intermittent ground faults. If a second 
phase is grounded, a short-circuit condition will occur and cause 
arcing between components. This could result in a methane-air 
explosion, cause failure of the enclosure, and expose miners to 
electrical shock. MSHA received a number of comments on this proposal.
    Some commenters stated that a grounded phase indicator light should 
be required on all high-voltage continuous mining machines. MSHA does 
not agree. This requirement is unnecessary when the three-phase power 
circuits onboard are grounded because the circuits are protected with 
ground-fault devices that automatically trip the circuit breaker at the 
power center. Currently, all 2,400-volt continuous mining machines have 
grounded-phase indicator light circuits because they have ungrounded 
power circuits onboard.
    Several commenters stated that lower voltage continuous mining 
machines and high-voltage shearing machines are not required to have a 
grounded-phase indicator light circuit and have operated many years 
without incident. They further stated that grounded-phase indictor 
light circuits are unnecessary and create a shock hazard for those who 
perform maintenance on the machine.
    In response, MSHA notes that lower voltage continuous mining 
machines and high-voltage shearing machines are designed differently 
from high-voltage continuous mining machines. Explosion-proof 
enclosures onboard low- and medium-voltage continuous mining machines 
and explosion-proof enclosures for high-voltage shearing machines are 
designed and tested to withstand arcing faults within the enclosure. On 
a high-voltage continuous

[[Page 17532]]

mining machine, however, only explosion-proof enclosures containing 
high-voltage switchgear are designed and tested to withstand internal 
arc faults. High-voltage continuous mining machines also have 
explosion-proof enclosures that do not contain high-voltage switchgear. 
These enclosures are not designed and tested to withstand high-energy 
arcing faults. Therefore, to prevent ignition hazards, the final rule 
requires indicator light circuits to assure that arcing does not occur 
and injure miners. Additionally, maintenance personnel are not exposed 
to shock hazards if they follow the troubleshooting and testing 
procedures specified in this final rule. MSHA believes that a greater 
hazard exists when a grounded-phase condition goes undetected.
    Final paragraph (e)(2), like the proposal, requires that the 
indicator light be installed so that the machine operator can readily 
observe it from any location where the continuous mining machine is 
normally operated. MSHA received no comments on this proposal.
    Final paragraph (e)(3), like the proposal, requires that the 
onboard ungrounded, three-phase power circuit have a test circuit for 
the grounded-phase indicator light circuit. It also requires that the 
test circuit be designed so that it can be activated without removing 
any enclosure covers and without creating a double-phase-to-ground 
fault. This requirement will assure proper operation of the indicator 
light circuit and that personnel conducting the test are not exposed to 
any hazard. MSHA received no comments on this proposal.
    Final paragraph (f) addresses the current carrying capacity, 
outside diameter, and the physical properties of high-voltage trailing 
cables. Unlike the proposal, the final rule does not incorporate by 
reference the Insulated Cable Engineer's Standards (ICEA) S-75-381/
National Electrical Manufacturer's Association (NEMA) Standard, NEMA WC 
58-1997, but rather includes a table for the outside diameters and 
ampacity ratings for high-voltage trailing cables. This table is 
referenced as Table 10 in Appendix I of 30 CFR Part 18, and is 
consistent with tables contained in the ICEA S-75-381/NEMA WC 58-1997. 
The purpose of the table is to standardize the ampacity and outer 
diameter of cables to ensure the interchangeability of trailing cables 
provided by different manufacturers.
    A commenter expressed concern that proposed paragraph (f) did not 
specifically limit trailing cable length. Existing Sec.  18.35(a)(5) 
specifies the maximum allowable lengths for trailing cables used to 
conduct electrical energy to production equipment, including continuous 
mining machines. For this reason, the Agency does not believe that it 
needs to limit trailing cable length in this provision.
    Final paragraph (f)(1), like the proposal, requires that trailing 
cables be constructed to include 100 percent semi-conductive tape 
shielding over each insulated power conductor. Final paragraph (f)(2) 
requires a grounded metallic braid shielding over each power conductor. 
The combination of semi-conductive tape and grounded metallic shielding 
around each power conductor provides symmetrical distribution of 
voltage stresses on the conductor insulation. Shielding also prevents 
transients on power systems. These provisions protect miners from shock 
and electrocution. MSHA received no comments on these proposals.
    Final paragraph (f)(3) requires that the cable include either a 
ground-check conductor not smaller than a No. 10 A.W.G., or a center 
ground-check conductor not smaller than a No. 16 A.W.G. stranded 
conductor. The term ``stranded'' has been added in the final rule to 
describe the No. 16 A.W.G. ground-check conductor for accuracy. The 
ground-check conductor is either located in the outer interstice of a 
trailing cable along with the grounding conductors or in the center of 
the trailing cable. Cables designed with a No. 16 A.W.G. center ground-
check conductor have been successfully used in high-voltage longwall 
applications for several years.
    A commenter indicated that the reference in the proposed preamble 
to the No. 16 A.W.G. ``stranded'' conductor describing the center 
ground-check conductor is technically incorrect, and suggested 
``special annular stranded with extensibility.'' MSHA does not agree. 
Cable manufacturers and ICEA/NEMA standards reference the center 
ground-check conductor as ``stranded.'' The terminology suggested by 
the commenter is a description of the quality of the No. 16 A.W.G. 
ground-check conductor and is consistent with the cable designs 
specified in the ICEA/NEMA standard.
    Final paragraph (f)(4), like the re-proposal, addresses the design 
and construction of high-voltage trailing cable jackets. MSHA received 
several comments on the proposal.
    Some commenters suggested that the final rule allow single-jacketed 
cables made of thermoplastic polyurethane (TPU) because of its high 
tensile strength and resistance to abrasion and tear. A commenter 
stated that the minimum tensile strengths for the single-jacketed and 
double-jacketed cables are 5,000 and 2,400 pounds per square inch, 
respectively; and tear strengths are 120 and 40 pounds per inch, 
respectively. The commenter also stated that the TPU material can be 
made in a color other than black, that TPU-jacketed trailing cables 
have been in use in the mining industry for 11 or 12 years, and that 
they have been used successfully on mining equipment such as shearing 
machines and medium-voltage continuous mining machines.
    Others stated that at least one granted PFM permitted the use of a 
TPU jacket as an alternative to the double-jacket requirement on two 
high-voltage continuous mining machines and on shuttle cars for over 
two years without any problems.
    Based on the comments, MSHA re-proposed paragraph (f)(4) to allow 
the option of using either a double-jacketed or a single-jacketed 
cable. The final rule contains requirements for both types of trailing 
cables.
    Final paragraph (f)(4)(i) requires that a double-jacketed cable, if 
used, consist of two reinforced layers of jacket material, with the 
inner layer a distinctive color from the outer layer. It also requires 
that black not be used for either layer. If used, a double-jacketed 
cable must have tear strength of more than 40 pounds per inch thickness 
and a tensile strength of more than 2,400 pounds per square inch.
    Final paragraph (f)(4)(ii) specifies the requirements for a single-
jacketed cable. If used, a single-jacketed cable must have tear 
strength of more than 100 pounds per inch thickness and a tensile 
strength of more than 4,000 pounds per square inch, and not be black in 
color. The final rule specifies the minimum values for the tear and 
tensile strength based on granted PFMs.
    In the re-proposal, MSHA requested comments on the minimum tear and 
tensile strength values for single-jacketed cables and received none.
    Final paragraph (g), like the proposal, requires manufacturers to 
provide safeguards against corona on all 4,160-volt circuits in 
explosion-proof enclosures.
    Corona is a luminous discharge that occurs around electric 
conductors that are subject to high electric stresses. Corona can cause 
premature breakdown of insulating materials in explosion-proof 
enclosures onboard the high-voltage continuous mining machine. This 
poses the risk of arcing and may result in explosion. Although corona 
usually does not present a hazard until a voltage of 8,000 volts is 
reached, safeguards should be taken at 4,160

[[Page 17533]]

volts, the maximum voltage permitted under Part 18. Safeguards include 
using cables with a corona-resistant insulation such as ethylene 
propylene to avoid small nicks or cuts in the cable insulation and to 
minimize high-voltage transients. MSHA received no comments on this 
proposal.
    Final paragraph (h), like the proposal, requires limiting the 
maximum explosion pressure rise within an enclosure to 0.83 times the 
design pressure for any explosion-proof enclosure containing high-
voltage switchgear. The requirement protects miners against explosion 
hazards that may arise from the effects of sustained high-voltage 
arcing faults. Arcing faults may significantly contribute to a pressure 
rise in an explosion-proof enclosure during an internal methane-air 
explosion. A pressure rise above the design limit of the enclosure can 
cause the explosion-proof enclosure to fail to contain the methane 
explosion. MSHA received no comments on the proposal.
    Final paragraph (i), like the proposal, prohibits high-voltage 
electrical components located in explosion-proof enclosures from being 
coplanar with a single-plane flame-arresting path. This provision 
prevents the heat or flame from an arc or methane explosion in an 
explosion-proof enclosure from igniting a methane-air mixture 
surrounding the enclosure by preventing conductor material particles 
from being expelled through the flame-arresting path. The possibility 
of this occurring with multi-plane flame-arresting path surfaces is 
non-existent because deflecting the path prevents ignitions by expelled 
particles. MSHA received no comments on this proposal.
    Final paragraph (j), like the proposal, requires that rigid 
insulation between high-voltage terminals (phase-to-phase or phase-to-
ground) be designed with creepage distances in accordance with the 
table specified in this section. The distances in the table provide 
adequate isolation to prevent a phase-to-phase or phase-to-ground fault 
that could cause a possible explosion. The required creepage distances 
are based on the phase-to-phase use voltage and the Comparative 
Tracking Index (CTI) of the insulation used. An appropriate method of 
determining the CTI of the electrical insulating material is described 
in the American Society for Testing and Materials Standard, ASTM D3638 
``Standard Test Method for Comparative Tracking Index of Electrical 
Insulating Materials.'' The creepage distances in the table are 
consistent with most commercially available high-voltage components to 
which this provision applies. MSHA received no comments on the 
proposal.
    Final paragraph (k), like the proposal, specifies minimum free 
distances (MFDs) in motor-starter enclosures. If the MFDs are below the 
values specified in the table, the enclosure could fail and cause an 
explosion. MFDs are distances between the wall or cover of an enclosure 
and uninsulated electrical conductors inside the enclosure. These MFDs 
are established to prevent wall or cover damage that might result from 
arcing.
    Final paragraph (k)(1), like the proposal, requires that values not 
specified in the table be calculated using a specific engineering 
formula. This formula is based on existing longwall requirements. Final 
paragraph (k)(2) requires that the MFD be increased by 1.5 inches for 
4,160-volt systems and by 0.7 inches for 2,400-volt systems when the 
adjacent wall area is the top of the enclosure. This increase in 
distance is necessary to account for the thermal effects of arcing due 
to heat rising within the enclosure. Final paragraph (k)(2) also 
addresses the use of a steel shield in conjunction with an aluminum 
wall or cover. Under these circumstances, the thickness of the steel 
shield is used to determine the MFD. MSHA received no comments on the 
proposal.
    Final paragraph (l), like the proposal, addresses static pressure 
testing of explosion-proof enclosures containing high-voltage 
switchgear. Final paragraph (l)(1) requires that, prior to performing 
the explosion tests, a static pressure test be performed on each 
prototype design of an explosion-proof enclosure housing high-voltage 
switchgear. It also establishes the static pressure testing and 
performance requirements for explosion-proof enclosures housing the 
high-voltage switchgear.
    Final paragraph (l)(2) requires that every explosion-proof 
enclosure containing high-voltage switchgear manufactured after the 
prototype was tested undergo a static pressure test or follow an MSHA-
accepted quality assurance procedure covering inspection of the 
enclosure. MSHA received no comments on this proposal.

B. Part 75--Mandatory Safety Standards--Underground Coal Mines

Section 75.823 High-Voltage Continuous Mining Machines; Scope
    Final Sec.  75.823 describes the scope of this standard. The 
standard addresses requirements for use of high-voltage continuous 
mining machines of up to 2,400 volts in underground coal mines. Final 
Sec.  75.823 also defines the term ``qualified person'' to mean a 
person meeting the requirements specified in existing Sec.  75.153.
    MSHA received no specific comments on this proposal. However, 
several comments relating to machine voltage are relevant here. One 
commenter agreed with the proposed rule which would have allowed 
machines to operate at 4,160-volts. Other commenters opposed allowing 
the voltage to exceed 2,400-volts, the limit in granted PFMs. They 
stated that the industry has no experience with 4,160-volt continuous 
mining machines and that these machines are more dangerous than 2,400-
volt machines.
    The final rule limits the voltage of the continuous mining machines 
to 2,400 volts because of the Agency's lack of experience with 4,160-
volt continuous mining machines in coal mines. Part 18, however, allows 
for approval of equipment up to 4,160 volts. Mine operators seeking 
MSHA approval to use 4,160-volt continuous mining machines would have 
to file a petition for modification.
Section 75.824 Electrical Protection
    Final Sec.  75.824 establishes the electrical protection 
requirements for high-voltage continuous mining machines. Effective 
electrical protection reduces the likelihood of ignitions, fires, and 
electrical shocks. With the exception of (a)(2)(ii), this section is 
based on granted PFMs. This section of the final rule is the same as 
the proposed rule except that non-substantive changes have been made 
for clarity.
    Final paragraph (a) requires the use of an adequate circuit-
interrupting device capable of providing short-circuit, overload, 
ground-fault, and under-voltage protection. The purpose of a circuit-
interrupting device is to interrupt the circuit in which it is used 
without damage to itself when subjected to the maximum voltage and 
current of the system. Short-circuit and overload protection prevent 
damage to cables and motors that can result from arcing and 
overheating. Ground-fault protection minimizes the risk of shock and 
electrocution. Under-voltage protection prevents the unintentional 
movement of equipment which can place miners at risk when power is lost 
and then restored.
    Final paragraph (a)(1)(i) specifies the current setting for a 
short-circuit protective device. The device is required to be set at 
the lower of: (1) The setting specified in the approval documentation, 
or (2) 75 percent of the minimum available phase-to-phase

[[Page 17534]]

short-circuit current at the continuous mining machine.
    The approval documentation specifies the maximum allowable setting 
of the breaker required to protect the trailing cable. This setting 
takes into consideration the cable size and length, and the motor 
starting current. If 75 percent of the minimum available short-circuit 
current is less than the setting specified in the approval, the breaker 
setting will be based on that amount.
    One commenter suggested that MSHA eliminate the phrase ``whichever 
is less'' from the rule to allow the design of systems that could 
utilize smaller cables and reduce injuries from handling cables. MSHA 
does not agree with this commenter. If the size of the trailing cable 
used is different than the cable size specified in the approval 
documentation, the machine would not be permissible. Furthermore, 
eliminating the words ``whichever is less,'' would allow the mine 
operator to set the circuit-interrupting device at a value that may 
cause it not to trip. For example, if the mine operator chooses to set 
the circuit-interrupting device at 1,200 amps as required in the 
approval, and 75 percent of the minimum available short-circuit current 
is only 750 amps, the circuit-interrupting device would not trip.
    Final paragraph (a)(1)(ii) revises the proposed rule to allow the 
short-circuit device protecting the trailing cable to have an 
intentional time delay not exceeding 0.050 seconds. The purpose of 
permitting a time delay is to eliminate nuisance tripping during motor 
starting.
    Proposed paragraph (a)(1)(ii) required that the time delay not 
exceed the setting specified in the approval documentation or 0.050 
seconds, whichever is less. After further review, MSHA found that the 
approval documentation does not specify a time delay. No comments were 
received on this proposal.
    Final paragraph (a)(2) establishes requirements for ground-fault 
protection.
    Final paragraph (a)(2)(i) requires a neutral grounding resistor to 
limit ground-fault currents to not more than 0.5 amps. Neutral 
grounding resistors are used in resistance grounded systems to limit 
the level of ground-fault current in a circuit. The use of a 0.5 amps 
neutral grounding resistor in conjunction with the ground-fault device 
specified in final paragraph (a)(2)(ii) will provide additional 
protection to miners from shock and fire hazards. MSHA received no 
comments on this proposal.
    Final paragraph (a)(2)(ii) requires that the circuit extending to 
the continuous mining machine be protected by a ground-fault device set 
at not more than 0.125 amps. The provision also allows a maximum time 
delay of up to 0.050 seconds. The 0.125-amps limit is based on MSHA's 
experience and knowledge that sensitive ground-fault devices are 
commercially available and have been successfully used to detect 
ground-fault currents. The ground-fault device would have to operate 
within 0.050 seconds when exposed to 0.125 amps or more. MSHA received 
no comments on this proposal.
    Final paragraph (a)(2)(iii) requires a look-ahead circuit to detect 
a ground-fault condition and prevent the closing of a circuit-
interrupting device when the ground-fault exists in a circuit. 
Detection of the ground-fault condition prior to energizing the circuit 
will protect miners from the risk of electrical shock. Additionally, 
the final rule incorporates the best practice to prevent the circuit-
interrupting device from repeatedly closing when a ground-fault 
condition exists because that could create a second ground-fault which 
would result in a short-circuit condition. MSHA received no comments on 
this proposal.
    Final paragraph (a)(2)(iv) requires a backup ground-fault device to 
detect an open neutral grounding resistor under a ground-fault 
condition. This device will provide additional protection. Once an open 
neutral grounding resistor is detected, the backup device will cause 
the circuit-interrupting device to de-energize that circuit at 40 
percent of the voltage developed across the resistor. This value 
provides a safety factor. Additionally, this provision allows the 
backup device to have a maximum time-delay setting of 0.250 seconds. 
The time-delay setting is low enough to assure quick de-energization of 
the circuit when the neutral resistor opens and a ground-fault exists, 
while also allowing for selective tripping with the ground-fault 
protective device in final paragraph (a)(2)(ii).
    One commenter had several concerns about this provision. The 
commenter stated that there were numerous problems with the potential 
transformer and voltage relay monitoring method as a backup device, 
which was used in MSHA's example. The commenter stated that potential 
transformers are not able to detect rectified faults because of 
ferroresonance. The potential transformer and voltage relay monitoring 
method has been widely used in the industry and MSHA is not aware of 
any problems associated with it. It is important to note that the 
proposal did not require the use of a particular backup device to 
detect an open neutral grounding resistor. Although MSHA listed this 
method as an example of a backup device in the proposal as one means of 
compliance, the Agency noted that other alternatives were acceptable.
    The commenter also expressed concern that the proposal did not 
include a requirement for detecting a shorted resistor. The commenter 
stated that a shorted grounding resistor will not limit the voltage on 
the frame of portable equipment to 100 volts or less. The purpose of 
requiring a backup device is to detect a ground-fault condition when 
the neutral grounding resistor is open. The commenter's recommendation 
is not necessary because the ground-fault protection required in final 
paragraph (a)(2)(ii) will detect that condition and de-energize the 
circuit.
    This commenter also suggested that the proposal be changed to 
require de-energization of the circuit within a certain time if the 
neutral grounding resistor opens, such as within 30 to 60 seconds. MSHA 
is not aware of any device that monitors a shorted neutral grounding 
resistor, nor does the Agency see the need for such a device. For the 
reasons stated above, no changes have been made to this section, and 
the final rule is the same as the proposal.
    Final paragraph (a)(2)(v), like the proposal, requires a thermal 
device to detect an overheated neutral grounding resistor caused by 
sustained ground-fault current, and de-energize the incoming power. 
This device provides an added safety measure for miners.
    The rule also requires that the overtemperature rating or setting 
of the device be the lower of: (1) 50 percent of the maximum 
temperature rise of the neutral grounding resistor, or (2) 302 [deg]F 
(150 [deg]C). Exposure of the neutral grounding resistor to sustained 
ground-fault currents generates heat which can cause the resistor to 
fail in the open mode. Failure of the resistor in an open mode will not 
provide ground-fault protection and increases the risk of shock 
hazards. The overtemperature setting requirement assures that the 
affected circuit is quickly de-energized under a sustained fault. 
MSHA's experience is that the temperature settings specified are high 
enough to prevent nuisance tripping while providing safe operating 
temperatures. Under the final rule, thermal protection must not be 
dependent on control power. This requirement recognizes that the loss 
of control power would prevent the operation of the detection device. 
Thermal protection includes, but is not

[[Page 17535]]

limited to, current transformers and thermal relays, thermostats, and 
other devices that sense overtemperature. MSHA did not receive any 
comments on the proposal.
    Final paragraph (a)(2)(vi), like the proposal, requires a single 
window-type current transformer to encircle the three-phase conductors 
to activate the ground-fault device required in final paragraph 
(a)(2)(ii). It also prohibits the equipment grounding conductors from 
passing through the current transformer as this defeats operation of 
the ground-fault device and eliminates protection. Using the single-
window type current transformer in conjunction with a ground-fault 
relay provides ground-fault protection for the circuit extending from 
the power center to the continuous mining machine. MSHA received no 
comments on this proposal.
    Final paragraph (a)(2)(vii), like the proposal, requires a ground-
fault test circuit for each ground-fault device. This provision 
requires that the test circuit inject no more than 50 percent of the 
current rating of the neutral grounding resistor through the current 
transformer. The purpose of the test circuit is to verify that a 
ground-fault condition will cause the corresponding circuit-
interrupting device to open. MSHA received no comments on this 
proposal.
    Final paragraph (a)(3), like the proposal, requires that the under-
voltage device operate on a loss of voltage, de-energize the circuit, 
and prevent the equipment from automatically restarting. This provision 
is performance-oriented, which allows any under-voltage protective 
device that will operate on loss of voltage and prevent the circuit-
interrupting device from automatically closing upon restoration of 
power. This requirement will reduce pinning and crushing risks to 
miners in case the equipment automatically restarts upon restoration of 
power. MSHA received no comments on this proposal.
    Final paragraph (b), like the proposal, prohibits use of circuit-
interrupting devices that automatically re-close after opening. 
Automatic re-closure allows a circuit that has been de-energized to 
become automatically re-energized. This provision will prevent 
automatic re-closing under fault conditions. Typically, faults occur in 
trailing cables due to damage from roof falls or when equipment runs 
over the cables. If this occurs, the use of a circuit-interrupting 
device designed to re-close automatically could present a risk of 
electrical shock and fire. MSHA received no comments on this proposal.
    Final paragraph (c) requires a mine operator to take certain 
actions when a grounded-phase indicator light, if used, indicates a 
grounded-phase condition. Detection of a grounded-phase condition will 
reduce risks of electrical shock and arcing. The capacitive coupling 
between each phase conductor and ground can subject an ungrounded 
circuit to dangerous over-voltages from intermittent ground faults, 
which in turn can lead to arcing and insulation failure. Arcing can 
ignite methane and create a hazard to miners. Insulation failure can 
lead to another phase-to-ground failure and create a shock hazard.
    Final paragraphs (c)(1) and (c)(2) specify the actions to be taken 
when a grounded-phase condition is indicated. Under paragraph (c)(1), 
once the indicator light shows that a grounded-phase condition has 
occurred, the machine must immediately be moved to an area where the 
roof is supported. This will minimize miners' exposure to roof falls 
while the equipment is being repaired. Final paragraph (c)(2) requires 
that that the grounded-phase condition be located and corrected prior 
to placing the machine back into operation. This requirement will 
protect miners from risks of electrical shocks.
    MSHA received a number of comments concerning the indicator light 
circuit, and has addressed these comments in Sec.  18.54(e). Except for 
minor editorial changes, the final provision is the same as the 
proposed rule.
Section 75.825 Power Centers
    Final Sec.  75.825 revises the proposal, and addresses the 
requirements for power centers that supply high-voltage continuous 
mining machines. The final rule includes provisions for disconnecting 
switches and devices, barriers and covers, interlocks, emergency stop 
switches, grounding sticks, and caution labels. These provisions reduce 
risks of electrical shocks, fires, and explosions.
    Final paragraph (a), like the proposal, requires a main 
disconnecting switch in the power center that supplies power to the 
high-voltage continuous mining machines. The main disconnecting switch, 
when open, must de-energize the input power to all power transformers 
in the power center. This will provide a safe means of de-energizing 
high-voltage circuits in the power center without affecting the feed-
through circuits. MSHA received no comments on the proposal.
    Final paragraph (b), like the proposal, requires a disconnecting 
device for each circuit that powers a continuous mining machine. 
Disconnecting devices in power centers de-energize the power to the 
machine. Power must be de-energized prior to performing electrical 
work.
    MSHA received no comments on this provision. In the final rule, 
MSHA has added clarifying language and defined ``disconnecting device'' 
as either a disconnecting switch or cable coupler.
    Final paragraph (c), which was paragraph (c)(7) in the proposal, 
addresses labeling, design, and installation requirements for 
disconnecting switches specified in this final rule. This provision 
requires that each switch be labeled to clearly identify the circuit 
that it disconnects. MSHA's experience is that identifying the circuit 
being de-energized by the switch assures that the proper circuit is de-
energized, which protects miners from exposure to electrical hazards. 
The design and installation requirements are specified in paragraphs 
(c)(1) through (c)(6) of the final rule.
    Final paragraphs (c)(1) and (c)(2), like the proposal, require each 
disconnecting switch to have voltage and current ratings compatible 
with the circuits in which they are used. Improperly rated switches can 
cause overheating and arcing and may create a shock or fire hazard for 
miners. MSHA received no comments on these proposals.
    Final paragraph (c)(3), like the proposal, requires that the 
disconnecting switch be designed and installed so that one can visually 
verify, without removing any covers, that the contacts of the device 
are open. If miners had to remove the cover to verify that the contacts 
are open, they could be exposed to energized high-voltage circuits and 
electrical shock risks. MSHA received no comments on the proposal.
    Final paragraph (c)(4), like the proposal, requires the 
disconnecting switch to ground all power conductors on the ``load'' 
side when the switch is in the ``open and grounded'' position. It 
assures the discharge of any voltage caused by capacitance between the 
power conductors and ground. Grounding the circuit on the load side 
reduces the risk of shocks to miners who are working on the trailing 
cable or continuous mining machine. MSHA received no comments on the 
proposal.
    Final paragraph (c)(5), like the proposal, requires that each 
disconnecting switch be designed so that it can only be locked when in 
the ``open and grounded'' position. A disconnecting switch that locks 
in the closed position could delay opening the switch during an 
emergency. This provision, in conjunction with the

[[Page 17536]]

requirements of final Sec.  75.831, assures that the circuit will 
remain de-energized until work is completed. MSHA received no comments 
on the proposal.
    Final paragraph (c)(6), like the proposal, requires that the 
disconnecting switch safely interrupt the full-load current in the 
circuit. A switch that is not capable of safely interrupting the full-
load current could result in its destruction and injuries to miners 
from flash burns or flying parts.
    The final rule provides an alternative if the switch is not 
designed to interrupt the full-load current of the circuit. It requires 
that the switch be designed to cause the circuit-interrupting device to 
automatically de-energize the incoming power before the disconnecting 
switch opens the circuit. MSHA received no comments on this provision 
and the requirement of the final rule is identical to the proposed 
rule.
    Final paragraph (d) requires all compartments that provide access 
to high-voltage conductors or parts to have barriers or covers to 
prevent miners from coming into contact with energized circuits.
    A commenter was concerned that the proposed rule would require that 
both a cover and a barrier be installed. This was not MSHA's intent. 
MSHA has revised the final rule to clarify that barriers or covers, or 
both, can be used.
    Final paragraph (e), like the proposal, addresses the interlocking 
requirements between the control circuit and the main disconnecting 
switch.
    Final paragraph (e)(1) requires that the interlock allow the 
control circuit to be energized through an auxiliary switch in the 
``test'' position only when the main disconnecting switch is in the 
``open and grounded'' position. When the main disconnecting switch is 
in the ``open and grounded'' position, the power conductors on the load 
side of the disconnecting switch are de-energized and grounded. The 
interlocking feature assures that, before the auxiliary switch can be 
placed in the ``test'' position, the main disconnecting switch is open 
and grounded.
    Final paragraph (e)(2), like the proposal, requires that when the 
main disconnecting switch is ``closed,'' the control circuit can only 
be powered through an auxiliary switch that is in the ``normal'' 
position. These requirements will prevent energization of the high-
voltage circuits during testing and troubleshooting. MSHA received no 
comments on the proposed paragraph (e).
    Final paragraph (f), like the proposal, was derived from granted 
PFMs. It requires that each cover or removable barrier of any 
compartment providing access to energized high-voltage conductors or 
parts have at least two interlock switches for the purpose of de-
energizing exposed high-voltage conductors or parts when the cover or 
barrier is removed. While the granted PFMs did not specify how many 
interlock switches were required, the proposed rule required a minimum 
of two interlock switches as an added safety measure to protect miners 
against accidental contact with energized high-voltage circuits.
    In the proposal, MSHA specifically requested comments on whether to 
add an exception for troubleshooting control circuits. A commenter 
suggested that each removable cover or barrier be interlocked to remove 
all power in the compartment before entering it, except when testing 
and troubleshooting control circuits. The commenter gave an example of 
some power centers that are designed with a circuit breaker in a 
separate incoming high-voltage compartment where the circuit breaker 
will remove power in other compartments instead of removing the 
incoming power.
    MSHA believes that it is crucial to miners' safety that incoming 
power be de-energized when miners remove covers prior to performing 
electrical work. De-energizing incoming power rather than only the 
power in the compartment being accessed assures that miners will not be 
exposed to energized high-voltage circuits.
    This commenter further suggested that MSHA require a single 
interlock switch instead of the two switches required in the proposed 
rule. The commenter stated that interlock switches expose miners to 
hazards when they troubleshoot failed switches. As noted in the 
proposal, MSHA has found that interlock switches might not operate 
effectively after exposure to the mine environment. To protect miners 
against accidental contact with energized high-voltage circuits, the 
final rule, like the proposal, requires two interlock switches to 
assure that at least one switch will function.
    Another commenter stated that MSHA should not allow an exception 
for troubleshooting control circuits in the high-voltage compartments. 
MSHA believes that miners who troubleshoot and test energized circuits 
in accordance with the provisions in this and other existing rules, 
will be protected.
    MSHA has considered comments and revised the proposal to allow 
troubleshooting and testing energized circuits when the control circuit 
is powered through an auxiliary switch in the ``test'' position.
    Final paragraph (g), like the proposal, requires that an emergency 
stop switch be located on the outside of the power center. The switch 
will de-energize the incoming high-voltage if an emergency arises. This 
provision also requires that the switch be hard-wired to a fail-safe 
ground-wire monitor. In emergency situations, reliability of the stop-
switch is critical. MSHA received no comments on the proposal.
    Final paragraph (h), like the proposal, requires that the power 
center be equipped with a grounding stick to be used to discharge 
capacitors and circuits before electrical work is performed. The 
purpose of the grounding stick is to assure that all high-voltage 
capacitors are discharged and that all circuits and components are de-
energized before electrical work is performed.
    Capacitors are energy storage devices; they continue to be 
energized even after the circuit is de-energized. Although some 
capacitors are supplied with bleed-off resistors, these resistors can 
open and the capacitor will continue to be energized. A disconnecting 
switch blade may stick in the closed position with the switch in the 
open position. If this happens, one or more phases of the circuit would 
remain energized. Use of a grounding stick provides a last line of 
defense to assure that the person performing electrical work will not 
be exposed to energized high-voltage circuits.
    Although there is no generally accepted definition, MSHA considers 
a grounding stick to be a live line tool (hot stick) made of either 
wood or fiberglass with a grounding attachment bonded to a No. \1/0\ 
A.W.G. copper grounding conductor. To safely discharge the capacitors 
and parts, the grounding conductor would need to be permanently bonded 
to the power center frame.
    The final rule requires that the power center have a label that 
identifies the location of the grounding stick to assure that the 
person performing the electrical work can easily find it. The rule 
requires that the grounding stick be stored in a dry location to 
maintain its effectiveness.
    A commenter suggested that MSHA allow alternatives to the grounding 
stick to discharge capacitors or circuits. At this time, MSHA is not 
aware of any alternatives to the grounding stick. This provision will 
assure that energy storing components and circuits are discharged and 
de-energized before miners come in contact with them.
    Another commenter agreed with the grounding stick requirement, 
stating that it will allow the safe discharge of stored energy and 
assure that miners

[[Page 17537]]

will not be exposed to high-voltage circuits. This commenter suggested 
that MSHA require steps to assure that energy stored in the cable after 
it is disconnected is discharged. Final paragraph (c)(4) requires that 
the disconnecting device ground all power conductors of the trailing 
cable when the device is in the ``open and grounded'' position. 
Therefore, MSHA has addressed this concern.
    A third commenter stated that power centers that have a visual 
disconnect should not be required to have a grounding stick. Although 
the visual disconnecting device de-energizes the circuit it 
disconnects, it does not discharge capacitors and other circuits. 
Therefore, MSHA has not adopted the comment.
    Based on comments, MSHA has clarified that the intent of the 
grounding stick is to discharge capacitors and de-energize high-voltage 
circuits.
    Final paragraph (i), like the proposal, requires that all 
compartments that provide access to energized high-voltage conductors 
and parts display a caution label that warns miners against entering 
the compartment before de-energizing the incoming high-voltage. The 
label serves as a reminder to miners that the line side of a 
disconnecting switch remains energized when the switch is opened unless 
the incoming power to the switch is de-energized. The Agency did not 
receive any comments on the proposal.
Section 75.826 High-Voltage Trailing Cables
    Final Sec.  75.826, like the proposal, is derived from existing 
Sec. Sec.  75.804 and 18.35 and specifies the requirements for high-
voltage trailing cables.
    Final paragraph (a) requires that the high-voltage trailing cable 
meet the design requirements of existing Sec.  18.35 and the approval 
requirements of high-voltage continuous mining machines.
    Final paragraph (b) allows two sizes of ground-check conductors 
depending on the cable design. The first option allows the use of a 
ground-check conductor not smaller than a No. 10 A.W.G. as required in 
existing Sec.  75.804. This minimum size is required because the 
ground-check conductor is located on the periphery of the cable and is 
subjected to more flexing and bending, weakening the conductor and 
resulting in possible breakage or damage. As an alternative, the cable 
can have a ground-check conductor not smaller than the No. 16 A.W.G. 
located in the center of the cable. This design does not subject the 
ground-check conductor to the same stresses as the No. 10 A.W.G. when 
the cable is flexed. The main advantage of this alternative is the 
reduction of inter-machine arcing because the cable design will include 
three grounding conductors placed symmetrically. This cable design has 
been used successfully with high-voltage longwall equipment. It 
eliminates the need to petition for modification of Sec.  75.804(a) 
when the cable is designed with a center ground-check conductor smaller 
than No. 10 A.W.G. but not smaller than a No. 16 A.W.G. No comments 
were received on the proposed section.
Section 75.827 Guarding of Trailing Cables
    Final Sec.  75.827 addresses requirements for guarding trailing 
cables. It renumbers proposed Sec.  75.827(c) and (d) as final 
paragraphs (a) and (b).
    Proposed Sec.  75.827(a) would have required the high-voltage 
trailing cable to be supported on insulators or placed in an unused 
entry from the power center to the last open crosscut during advance 
mining, to within 150 feet outby any pillar workings during second 
mining, and to within 150 feet of the continuous mining machine when 
used in outby areas.
    Some commenters were concerned that supporting the cable on 
insulators may subject shuttle or ram car operators to injuries if the 
cable is supported at canopy height. They stated that in muddy 
conditions, shuttle or ram cars could slide into the coal ribs and 
cause the equipment to hit and damage the cable, exposing the equipment 
operators to possible arc burns and electrical shock. They also stated 
that by placing the cable on the floor, the machine tires and not the 
canopy would hit the cable, and any resulting hazard would occur away 
from the machine operator. Other commenters agreed with the proposed 
language requiring that the cables be supported on insulators but 
suggested that the cable be installed only when it is de-energized. 
Others suggested that the cable be installed on insulators at a minimum 
height of 6.5 feet and 7.5 feet.
    Commenters stated that an unused entry may not always be available 
to meet the proposed requirement to place the cable in an unused entry. 
After evaluating the comments, MSHA agrees that suspending the cable 
may be more of a hazard to miners than placing the cable on the mine 
floor. MSHA also agrees that an unused entry may not always be 
available. Therefore, the final rule does not contain the proposed 
requirements that the cable must be supported or placed in an unused 
entry.
    Proposed Sec.  75.827(b) permitted the temporary storage of cables 
on a sled or in a crosscut located between the power center and the 
last open crosscut. It required these storage locations to be 
barricaded and to have warning signs posted.
    One commenter stated that in many cases, allowing temporary storage 
of trailing cables at the locations in the proposal would encourage 
storage of cables in mining sections, posing a safety threat to miners. 
The commenter further stated that the proposal was not practical or 
safe. In response to comments, the final rule does not contain the 
requirement for temporary storage of cables.
    One commenter stated that the requirements of Sec.  75.827 are 
excessive because the cable leaving the power center is the safest 
cable on the section and should not be required to meet additional 
requirements. MSHA does not agree with this commenter because the cable 
is still susceptible to damage by mobile equipment. Consequently, 
guarding and protecting the cable from damage by mobile equipment are 
important safety measures for the protection of miners.
    Proposed Sec.  75.827(c), redesignated as final Sec.  75.827(a), 
addresses guarding of the trailing cable. Final paragraph (a)(1) 
specifies the locations where the high-voltage trailing cable must be 
guarded. These locations are: (1) From the power center cable coupler 
for a distance of 10 feet inby the power center; (2) from the entrance 
gland for a distance of 10 feet outby the last strain clamp on the 
continuous mining machine; and (3) any location where the cable could 
be damaged by moving equipment. These are locations where miners are 
likely to come in contact with the cable and where the cable could be 
damaged. To be effectively guarded, the cable must be fully covered, so 
that there is a physical barrier between the cables and miners. One 
commenter suggested that the trailing cable be guarded for 10 feet inby 
the power center. MSHA agrees that this is the location that miners are 
most likely to come in contact with the cable. In response to comments, 
the final rule requires that the cable be guarded for 10 feet inby the 
power center. The proposed requirement for guarding the trailing cable 
between the power center and the first cable insulator is not included 
in the final rule since insulators are not required.
    Final paragraph (a)(1)(ii) requires that the high-voltage trailing 
cable be guarded from the entrance gland for a distance of 10 feet 
outby the last strain clamp on the continuous mining machine. The 
proposal required guarding for a ``minimum'' of 10 feet. Some 
commenters suggested that this distance be increased from 10 feet to 35 
feet or more. The proposal would have

[[Page 17538]]

allowed guarding for a distance of 35 feet or more. However, requiring 
guarding for a distance longer than 10 feet, as suggested by the 
commenters, would preclude detection of a damaged cable in the guarded 
area because the final rule does not require removal of guarding when 
inspecting the cable. The final rule does not contain the term minimum 
and does not require guarding beyond 10 feet.
    Final paragraph (a)(1)(iii), like the proposal, requires guarding 
at any location where the cable could be damaged by moving equipment. 
MSHA received no comments on this proposal.
    Final paragraph (a)(2), like the proposal, requires that guarding 
be constructed of nonconductive flame-resistant material, or grounded 
metal. If a marking does not appear on the guarding to indicate that it 
is flame-resistant, MSHA will request documentation to substantiate 
that the material is flame-resistant. Metal and non-conductive guarding 
may be of a continuous length or overlapping shorter pieces. Shorter 
pieces of metal guarding must be bonded together to assure a continuous 
metallic path. MSHA received no comments on this proposal.
    Final paragraph (b) addresses requirements when equipment must 
cross any portion of the cable. It allows two alternatives for 
protecting the cable from mobile equipment: (1) Suspension of the cable 
from the mine roof; or (2) the use of commercially