[Code of Federal Regulations]
[Title 30, Volume 1]
[Revised as of July 1, 2006]
From the U.S. Government Printing Office via GPO Access
[CITE: 30CFR18.53]
[Page 111-113]
TITLE 30--MINERAL RESOURCES
CHAPTER I--MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR
PART 18_ELECTRIC MOTOR-DRIVEN MINE EQUIPMENT AND ACCESSORIES--Table of
Contents
Subpart B_Construction and Design Requirements
Sec. 18.53 High-voltage longwall mining systems.
(a) In each high-voltage motor-starter enclosure, with the exception
of a controller on a high-voltage shearer, the disconnect device
compartment, control/communications compartment, and motor contactor
compartment must be separated by barriers or partitions to prevent
exposure of personnel to energized high-voltage conductors or parts. In
each motor-starter enclosure on a high-voltage shearer, the high-voltage
components must be separated from lower voltage components by barriers
or partitions to prevent exposure of personnel to energized high-voltage
conductors or parts. Barriers or partitions must be constructed of
grounded metal or nonconductive insulating board.
(b) Each cover of a compartment in the high-voltage motor-starter
enclosure containing high-voltage components must be equipped with at
least two interlock switches arranged to automatically deenergize the
high-voltage components within that compartment when the cover is
removed.
(c) Circuit-interrupting devices must be designed and installed to
prevent automatic reclosure.
(d) Transformers with high-voltage primary windings that supply
control voltages must incorporate grounded electrostatic (Faraday)
shielding between the primary and secondary windings. The shielding must
be connected to equipment ground by a minimum No. 12 AWG grounding
conductor. The secondary nominal voltage must not exceed 120 volts, line
to line.
(e) Test circuits must be provided for checking the condition of
ground-wire monitors and ground-fault protection without exposing
personnel to energized circuits. Each ground-test circuit must inject a
primary current of 50 percent or less of the current rating of the
grounding resistor through the current transformer and cause each
corresponding circuit-interrupting device to open.
(f) Each motor-starter enclosure, with the exception of a controller
on a high-voltage shearer, must be equipped with a disconnect device
installed to deenergize all high-voltage power conductors extending from
the enclosure when the device is in the ``open'' position.
(1) When multiple disconnect devices located in the same enclosure
are used to satisfy the above requirement they must be mechanically
connected to provide simultaneous operation by one handle.
(2) The disconnect device must be rated for the maximum phase-to-
phase voltage and the full-load current of the circuit in which it is
located, and installed so that--
(i) Visual observation determines that the contacts are open without
removing any cover;
(ii) The load-side power conductors are grounded when the device is
in the ``open'' position;
(iii) The device can be locked in the ``open'' position;
(iv) When located in an explosion-proof enclosure, the device must
be designed and installed to cause the current to be interrupted
automatically prior to the opening of the contacts; and
(v) When located in a non-explosion-proof enclosure, the device must
be designed and installed to cause the current to be interrupted
automatically prior to the opening of the contacts, or
[[Page 112]]
the device must be capable of interrupting the full-load current of the
circuit.
(g) Control circuits for the high-voltage motor starters must be
interlocked with the disconnect device so that--
(1) The control circuit can be operated with an auxiliary switch in
the ``test'' position only when the disconnect device is in the open and
grounded position; and
(2) The control circuit can be operated with the auxiliary switch in
the ``normal'' position only when the disconnect switch is in the closed
position.
(h) A study to determine the minimum available fault current must be
submitted to MSHA to ensure adequate protection for the length and
conductor size of the longwall motor, shearer and trailing cables.
(i) Longwall motor and shearer cables with nominal voltages greater
than 660 volts must be made of a shielded construction with a grounded
metallic shield around each power conductor.
(j) High-voltage motor and shearer circuits must be provided with
instantaneous ground-fault protection of not more than 0.125-amperes.
Current transformers used for this protection must be of the single-
window type and must be installed to encircle all three phase
conductors.
(k) Safeguards against corona must be provided on all 4,160 voltage
circuits in explosion-proof enclosures.
(l) The maximum pressure rise within an explosion-proof enclosure
containing high-voltage switchgear must be limited to 0.83 times the
design pressure.
(m) High-voltage electrical components located in high-voltage
explosion-proof enclosures must not be coplanar with a single plane
flame-arresting path.
(n) Rigid insulation between high-voltage terminals (Phase-to-Phase
or Phase-to-Ground) must be designed with creepage distances in
accordance with the following table:
Minimum Creepage Distances
--------------------------------------------------------------------------------------------------------------------------------------------------------
Minimum creepage distances (inches) for comparative tracking index
(CTI) range \1\
Phase to phase voltage Points of measure ----------------------------------------------------------------------
CTI=500 380<=CTI<500 175<=CTI<380 CTI<175
--------------------------------------------------------------------------------------------------------------------------------------------------------
2,400.......................................... 0-0 1.50 1.95 2.40 2.90
0-G 1.00 1.25 1.55 1.85
4,160.......................................... 0-0 2.40 3.15 3.90 4.65
0-G 1.50 1.95 2.40 2.90
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Assumes that all insulation is rated for the applied voltage or higher.
(o) Explosion-proof motor-starter enclosures must be designed to
establish the minimum free distance (MFD) between the wall or cover of
the enclosure and uninsulated electrical conductors inside the enclosure
in accordance with the following table:
High-Voltage Minimum Free Distances (MFD)
----------------------------------------------------------------------------------------------------------------
Steel MFD (in) Aluminum MFD (in)
Wall/cover thickness (in) -----------------------------------------------------------------------------
A \1\ B \2\ C \3\ A B C
----------------------------------------------------------------------------------------------------------------
\1/4\............................. 2.8 4.3 5.8 \4\ NA \4\ NA \4\ NA
\3/8\............................. 1.8 2.3 3.9 8.6 12.8 18.1
\1/2\............................. * 1.2 2.0 2.7 6.5 9.8 13.0
\5/8\............................. * 0.9 1.5 2.1 5.1 7.7 10.4
\3/4\............................. * 0.6 * 1.1 1.6 4.1 6.3 8.6
1................................. (*) * 0.6 * 1.0 2.9 4.5 6.2
----------------------------------------------------------------------------------------------------------------
Note: * The minimum electrical clearances must still be maintained.
\1\ Column A specifies the MFD for enclosures that have available 3-phase bolted short-circuit currents of
10,000 amperes rms or less.
\2\ Column B specifies the MFD for enclosures that have a maximum available 3-phase bolted short-circuit
currents greater than 10,000 and less than or equal to 15,000 amperes rms.
\3\ Column C specifies the MFD for enclosures that have a maximum available 3-phase bolted short-circuit
currents greater than 15,000 and less than or equal to 20,000 amperes rms.
[[Page 113]]
\4\ Not Applicable--MSHA doesn't allow aluminum wall or covers to be \1/4\ inch or less in thickness (Section
18.31).
(1) For values not included in the table, the following formulas on
which the table is based may be used to determine the minimum free
distance.
(i) Steel Wall/Cover:
[GRAPHIC] [TIFF OMITTED] TR23NO04.000
(ii) Aluminum Wall/Cover:
[GRAPHIC] [TIFF OMITTED] TR23NO04.001
Where C is 1.4 for 2,400 volt systems or 3.0 for 4,160 volt systems,
Isc is the 3-phase short circuit current in amperes of the
system, t is the clearing time in seconds of the outby circuit-
interrupting device and d is the thickness in inches of the metal wall/
cover adjacent to an area of potential arcing.
(2) The minimum free distance must be increased by 1.5 inches for
4,160 volt systems and 0.7 inches for 2,400 volt systems when the
adjacent wall area is the top of the enclosure. If a steel shield is
mounted in conjunction with an aluminum wall or cover, the thickness of
the steel shield is used to determine the minimum free distances.
(p) The following static pressure test must be performed on each
prototype design of explosion-proof enclosures containing high-voltage
switchgear prior to the explosion tests. The static pressure test must
also be performed on every explosion-proof enclosure containing high-
voltage switchgear, at the time of manufacture, unless the manufacturer
uses an MSHA accepted quality assurance procedure covering inspection of
the enclosure. Procedures must include a detailed check of parts against
the drawings to determine that the parts and the drawings coincide and
that the minimum requirements stated in part 18 have been followed with
respect to materials, dimensions, configuration and workmanship.
(1) Test procedure. (i) The enclosure must be internally pressurized
to at least the design pressure, maintaining the pressure for a minimum
of 10 seconds.
(ii) Following the pressure hold, the pressure must be removed and
the pressurizing agent removed from the enclosure.
(2) Acceptable performance. (i) The enclosure during pressurization
must not exhibit--
(A) Leakage through welds or casting; or
(B) Rupture of any part that affects the explosion-proof integrity
of the enclosure.
(ii) The enclosure following removal of the pressurizing agents must
not exhibit--
(A) Visible cracks in welds;
(B) Permanent deformation exceeding 0.040 inches per linear foot; or
(C) Excessive clearances along flame-arresting paths following
retightening of fastenings, as necessary.
[67 FR 10999, Mar. 11, 2002; 69 FR 68078, Nov. 23, 2004; 69 FR 70752,
Dec. 7, 2004]