
[Code of Federal Regulations]
[Title 30, Volume 1]
[Revised as of July 1, 2001]
From the U.S. Government Printing Office via GPO Access
[CITE: 30CFR7]

[Page 58-76]
 
                       TITLE 30--MINERAL RESOURCES
 
  CHAPTER I--MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR
 
PART 7--TESTING BY APPLICANT OR THIRD PARTY--Table of Contents
 
Subpart J--Electric Motor Assemblies

    Source: 57 FR 61193, Dec. 23, 1992, unless otherwise noted.

Sec. 7.301  Purpose and effective date.

    This subpart establishes the specific requirements for MSHA approval 
of certain explosion-proof electric motor assemblies intended for use in 
approved equipment in underground mines. Applications for approval or 
extensions of approval submitted after February 22, 1996 shall meet the 
requirements of this part. Those motors that incorporate features not 
specifically addressed in this subpart will continue to

[[Page 59]]

be evaluated under part 18 of this chapter.

Sec. 7.302  Definitions.

    The following definitions apply in this subpart:
    Afterburning. The combustion of any flammable mixture that is drawn 
into an enclosure after an internal explosion in the enclosure. This 
condition is determined through detection of secondary pressure peaks 
occurring subsequent to the initial explosion.
    Cylindrical joint. A joint comprised of two contiguous, concentric, 
cylindrical surfaces.
    Explosion-proof enclosure. A metallic enclosure used as a winding 
compartment, conduit box, or a combination of both that complies with 
the applicable requirements of Sec. 7.304 of this part and is 
constructed so that it will withstand the explosion tests of Sec. 7.306 
of this part.
    Fastening. A bolt, screw, or stud used to secure adjoining parts to 
prevent the escape of flame from an explosion-proof enclosure.
    Flame-arresting path. Two or more adjoining or adjacent surfaces 
between which the escape of flame is prevented.
    Internal free volume (of an empty enclosure). The volume remaining 
after deducting the volume of any part that is essential in maintaining 
the explosion-proof integrity of the enclosure or necessary for 
operation of the motor. Essential parts include the parts that 
constitute the flame-arresting path and those necessary to secure parts 
that constitute a flame-arresting path.
    Motor assembly. The winding compartment including a conduit box when 
specified. A motor assembly is comprised of one or more explosion-proof 
enclosures.
    Plane joint. A joint comprised of two adjoining surfaces in parallel 
planes.
    Step (rabbet) joint. A joint comprised of two adjoining surfaces 
with a change or changes in direction between its inner and outer edges. 
A step joint may be composed of a cylindrical portion and a plane 
portion or of two or more plane portions.
    Stuffing box. An entrance with a recess filled with packing material 
for cables extending through a wall of an explosion-proof enclosure.
    Threaded joint. A joint consisting of a male- and a female-threaded 
member, both of which are the same type and gauge.

Sec. 7.303  Application requirements.

    (a) An application for approval of a motor assembly shall include a 
composite drawing or drawings with the following information:
    (1) Model (type), frame size, and rating of the motor assembly.
    (2) Overall dimensions of the motor assembly, including conduit box 
if applicable, and internal free volume.
    (3) Material and quantity for each of the component parts that form 
the explosion-proof enclosure or enclosures.
    (4) All dimensions (including tolerances) and specifications 
required to ascertain compliance with the requirements of Sec. 7.304 of 
this part.
    (b) All drawings shall be titled, dated, numbered, and include the 
latest revision.

Sec. 7.304  Technical requirements.

    (a) Voltage rating of the motor shall not exceed 4160 volts.
    (b) The temperature of the external surfaces of the motor assembly 
shall not exceed 150  deg.C (302  deg.F) when operated at the 
manufacturers' specified ratings.
    (c) Minimum clearances between uninsulated electrical conductor 
surfaces, or between uninsulated conductor surfaces and grounded metal 
surfaces, within the enclosure shall meet the requirements of table J-1 
of this section.

       Table J-1--Minimum Clearances Between Uninsulated Surfaces
------------------------------------------------------------------------
                                                    Clearances (inches)
                                                 -----------------------
                                                               Phase-to-
          Phase-to-phase voltage (rms)             Phase-to-   ground or
                                                     phase      control
                                                                circuit
------------------------------------------------------------------------
0 to 250........................................        0.25        0.25
251 to 600......................................        0.28        0.25
601 to 1000.....................................        0.61        0.25
1001 to 2400....................................        1.4         0.6
2401 to 4160....................................        3.0         1.4
------------------------------------------------------------------------

    (d) Parts whose dimensions can change with the motor operation, such 
as ball and roller bearings and oil seals, shall not be used as flame-
arresting paths.

[[Page 60]]

    (e) The widths of any grooves, such as grooves for holding oil seals 
or o-rings, shall be deducted in measuring the widths of flame-arresting 
paths.
    (f) An outer bearing cap shall not be considered as forming any part 
of a flame-arresting path unless the cap is used as a bearing cartridge.
    (g) Requirements for explosion-proof enclosures of motor assemblies.
    (1) Enclosures shall be--
    (i) Constructed of metal;
    (ii) Designed to withstand a minimum internal pressure of 150 pounds 
per square inch (gauge);
    (iii) Free from blowholes when cast; and
    (iv) Explosion proof as determined by the tests set out in 
Sec. 7.306 of this part.
    (2) Welded joints forming an enclosure shall be--
    (i) Continuous and gas-tight; and
    (ii) Made in accordance with or exceed the American Welding Society 
Standard AWS D14.4-77, ``Classification and Application of Welded Joints 
for Machinery and Equipment,'' or meet the test requirements set out in 
Sec. 7.307 of this part. AWS D14.4-77 is incorporated by reference and 
has been approved by the Director of the Federal Register in accordance 
with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from the 
American Welding Society, Inc., 2501 NW 7th Street, Miami, FL 33125. 
Copies may be inspected at the Mine Safety and Health Administration, 
Department of Labor, Approval and Certification Center, RR 1, Industrial 
Park Road, Triadelphia, WV 26059, or at the Office of the Federal 
Register, 800 N. Capitol Street, NW., 7th Floor, suite 700, Washington, 
DC.
    (3) External rotating parts shall not be constructed of aluminum 
alloys containing more than 0.6 percent magnesium. Non-metallic rotating 
parts shall be provided with a means to prevent an accumulation of 
static electricity.
    (4) Threaded covers and mating parts shall be designed with Class 1A 
and 1B (coarse, loose fitting) threads. The covers shall be secured 
against loosening.
    (5) Flat surfaces between fastening holes that form any part of a 
flame-arresting path shall be plane to within a maximum deviation of 
one-half the maximum clearance specified in paragraph (g)(19) of this 
section. All surfaces forming a flame-arresting path shall be finished 
during the manufacturing process to not more than 250 microinches. A 
thin film of nonhardening preparation to inhibit rusting may be applied 
to these finished metal surfaces as long as the final surface can be 
readily wiped free of any foreign materials.
    (6) For a laminated stator frame, it shall be impossible to insert a 
0.0015 inch thickness gauge to a depth exceeding \1/8\ inch between 
adjacent laminations or between end rings and laminations.
    (7) Lockwashers, or equivalent, shall be provided for all 
fastenings. Devices other than lockwashers shall meet the requirements 
of Sec. 7.308 of this part. Equivalent devices shall only be used in the 
configuration in which they were tested.
    (8) Fastenings shall be as uniform in size as practicable to 
preclude improper installation.
    (9) Holes for fastenings in an explosion-proof enclosure shall be 
threaded to ensure that all specified bolts or screws will not bottom 
even if the washers are omitted.
    (10) Holes for fastenings shall not penetrate to the interior of an 
explosion-proof enclosure, except holes made through motor casings for 
bolts, studs, or screws to hold essential parts, such as pole pieces, 
brush rigging, and bearing cartridges. The attachments of such parts 
shall be secured against loosening. The threaded holes in these parts 
shall be blind unless the fastenings are inserted from the inside, in 
which case the fastenings shall not be accessible with the rotor in 
place.
    (11) For direct current motor assemblies with narrow interpoles, the 
distance from the edge of the pole piece to any bolt hole in the frame 
shall be at least \1/8\ inch. If the distance is \1/8\ to \1/4\ inch, 
the diametrical clearance for the pole bolt shall not exceed \1/64\ inch 
for not less than \1/2\ inch through the frame. Furthermore, the pole 
piece shall have the same radius as the inner surface of the frame. Pole 
pieces may be shimmed as necessary. If used, the total resulting 
thickness of the shims shall be specified. The shim assembly

[[Page 61]]

shall meet the same requirements as the pole piece.
    (12) Coil-thread inserts, if used in holes for fastenings, shall 
meet the following:
    (i) The inserts shall have internal screw threads.
    (ii) The holes for the inserts shall be drilled and tapped 
consistent with the insert manufacturer's specifications.
    (iii) The inserts shall be installed consistent with the insert 
manufacturer's specifications.
    (iv) The insert shall be of sufficient length to ensure the minimum 
thread engagement of fastening specified in paragraph (g)(19) of this 
section.
    (13) A minimum of \1/8\ inch of stock shall be left at the center of 
the bottom of each blind hole that could penetrate into the interior of 
an explosion-proof enclosure.
    (14) Fastenings shall be used only for attaching parts that are 
essential in maintaining the explosion-proof integrity of the enclosure, 
or necessary for the operation of the motor. They shall not be used for 
making electrical connections.
    (15) Through holes not in use shall be closed with a metal plug. 
Plugs, including eyebolts, in through holes where future access is 
desired shall meet the flame-arresting paths, lengths, and clearances of 
paragraph (g)(19) of this section and be secured by spot welding or 
brazing. The spot weld or braze may be on a plug, clamp, or fastening 
(for example see figure J-1). Plugs for holes where future access is not 
desired shall be secured all around by a continuous gas-tight weld.
    (16) O-rings, if used in a flame-arresting path, shall meet the 
following:
    (i) When the flame-arresting path is in one plane, the o-ring shall 
be located at least one-half the acceptable flame-arresting path length 
specified in paragraph (g)(19) of this section from within the outside 
edge of the path (see figure J-2).
    (ii) When the flame-arresting path is one of the plane-cylindrical 
type (step joint), the o-ring shall be located at least \1/2\ inch from 
within the outer edge of the plane portion (see figure J-3), or at the 
junction of the plane and cylindrical portion of the joint (see figure 
J-4), or in the cylindrical portion (see figure J-5).
    (17) Mating parts comprising a pressed fit shall result in a minimum 
interference of 0.001 inch between the parts. The minimum length of the 
pressed fit shall be equal to the minimum thickness requirement of 
paragraph (g)(19) of this section for the material in which the fit is 
made.
    (18) The flame-arresting path of threaded joints shall conform to 
the requirements of paragraph (g)(19) of this section.
    (19) Explosion-proof enclosures shall meet the requirements set out 
in table J-2 of this section, based on the internal free volume of the 
empty enclosure.

                             Table J-2--Explosion-Proof Requirements Based on V
olume
-------------------------------------------------------------------------------
---------------------------------
                                                                             Vo
lume of empty enclosure
                                                                 --------------
---------------------------------
                                                                   Less than 45
    45 to 124 cu.   More than 124
                                                                     cu. ins.  
   ins. inclusive     cu. ins.
-------------------------------------------------------------------------------
---------------------------------
Minimum thickness of material for walls \1\.....................          \1/8\
"         \3/16\"          \1/4\"
Minimum thickness of material for flanges and covers............      \2\ \1/4\
"      \3\ \3/8\"      \3\ \1/2\"
Minimum width of joint; all in one plane........................          \1/2\
"          \3/4\"              1"
Maximum clearance; joint all in one plane.......................          0.002
"          0.003"          0.004"
Minimum width of joint, portions of which are in different            \4\ \3/8\
"      \4\ \5/8\"      \4\ \3/4\"
 planes; cylinders or equivalent................................
Maximum clearances; joint in two or more planes, cylinders or
 equivalent: \5\
    (a) Portion perpendicular to plane \6\......................          0.008
"          0.008"          0.008"
    (b) Plane portion...........................................          0.006
"          0.006"          0.006"
Maximum fastening <SUP>7,</SUP> <SUP>8</SUP> spacing; joints all in one plane..
.......          (\16\)          (\16\)          (\16\)
Maximum fastening spacing; joints, portions of which are in               (\17\
)          (\17\)          (\17\)
 different planes...............................................
Minimum diameter of fastening \9\ (without regard to type of              \1/4\
"          \1/4\"          \3/8\"
 joint).........................................................
Minimum thread engagement of fastening \10\.....................          \1/4\
"          \1/4\"          \3/8\"
Maximum diametrical clearance between fastening body and                 \1/64\
"         \1/32\"         \1/16\"
 unthreaded holes through which it passes <SUP>8,11,12</SUP>...............
Minimum distance from interior of enclosure to the edge of a      .............
.  ..............  ..............
 fastening hole: <SUP>8,13</SUP>
    Joint--minimum width 1".....................................  .............
.  ..............    \14\ \7/16\"

[[Page 62]]


    Joint--less than 1" wide....................................          \1/8\
"         \3/16\"  ..............
-------------------------------------------------------------------------------
---------------------------------
                                               Cylindrical Joints
-------------------------------------------------------------------------------
---------------------------------
Shaft centered by ball or roller bearings:
  Minimum length of flame-arresting path........................          \1/2\
"          \3/4\"              1"
  Maximum diametrical clearance.................................          0.020
"          0.025"          0.030"
Other cylindrical joints: \15\
    Minimum length of flame-arresting path......................          \1/2\
"          \3/4\"              1"
    Maximum diametrical clearance...............................          0.006
"          0.008"          0.010"
-------------------------------------------------------------------------------
---------------------------------
\1\ This is the minimal nominal dimension when applied to standard steel plate.
\2\ \1/32\ inch less is allowable for machining rolled plate.
\3\ \1/16\ inch less is allowable for machining rolled plate.
\4\ If only two planes are involved, neither portion of a joint shall be less t
han \1/8\ inch wide, unless the
  wider portion conforms to the same requirements as those for a joint that is 
all in one plane. If more than
  two planes are involved (as in labyrinths or tongue-and-groove joints) the co
mbined lengths of those portions
  having prescribed clearances are considered.
\5\ For winding compartments having internal free volume not exceeding 350 cubi
c inches and joints not exceeding
  32 inches in outer circumference and provided with step joints between the st
ator frame and the end bracket
  the following dimensions shall apply:


                                    Dimensions of Rabbet (Step) Joints-Inches
                                          [See figure J-6 in appendix]
-------------------------------------------------------------------------------
---------------------------------
                                                                               
                       Maximum
                                                                   Minimum widt
h      Maximum       diametrical
                       Minimum total width                          of clamped 
    clearance of    clearance at
                                                                  radial portio
n  radial portion   axial portion
-------------------------------------------------------------------------------
---------------------------------
\3/8\...........................................................          \3/64
\          0.0015           0.003
\1/2\...........................................................          \3/64
\           0.002           0.003
\1/2\...........................................................          \3/32
\           0.002           0.004
-------------------------------------------------------------------------------
---------------------------------
\6\ The allowable diametrical clearance is 0.008 inch when the portion perpendi
cular to the plane portion is \1/
  4\ inch or greater in length. If the perpendicular portion is more than \1/8\
 inch but less than \1/4\ inch
  wide, the diametrical clearance shall not exceed 0.006 inch.
\7\ Studs, when provided, shall bottom in blind holes, be completely welded in 
place, or have the bottom of the
  hole closed with a plug secured by weld or braze. Fastenings shall be provide
d at all corners.
\8\ The requirements as to diametrical clearance around the fastening and minim
um distance from the fastening
  hole to the inside of the explosion-proof enclosure apply to steel dowel pins
. In addition, when such pins are
  used, the spacing between centers of the fastenings on either side of the pin
 shall not exceed 5 inches.
\9\ Fastening diameters smaller than specified may be used if the enclosure mee
ts the test requirements of 30
  CFR 7.307 and then 7.306 in that order.
\10\ Minimum thread engagement shall be equal to or greater than the diameter o
f the fastening specified, or the
  enclosure must meet the test requirements of 30 CFR 7.307 and then 7.306 in t
hat order.
\11\ This maximum clearance applies only when the fastening is located within t
he flame-arresting path.
\12\ Threaded holes for fastening bolts shall be machined to remove burrs or pr
ojections that affect planarity
  of a surface forming a flame-arresting path.
\13\ Edge of the fastening hole shall include the edge of any machining done to
 the fastening hole, such as
  chamfering.
\14\ If the diametrical clearance for fastenings does not exceed \1/32\ inch, t
hen the minimum distance shall be
  \1/4\ inch.
\15\ Shafts or operating rods through journal bearings shall be at least \1/4\"
 in diameter. The length of the
  flame-arresting path shall not be reduced when a pushbutton is depressed. Ope
rating rods shall have a shoulder
  or head on the portion inside the enclosure. Essential parts riveted or bolte
d to the inside portion are
  acceptable in lieu of a head or shoulder, but cotter pins and similar devices
 shall not be used.
\16\ 6" with a minimum of 4 fastenings.
\17\ 8" with a minimum of 4 fastenings.

    (h) Lead entrances. (1) Each cable, which extends through an outside 
wall of the motor assembly, shall pass through a stuffing-box lead 
entrance (see figure J-7). All sharp edges shall be removed from 
stuffing boxes, packing nuts, and other lead entrance (gland) parts, so 
that the cable jacket is not damaged.
    (2) When the packing is properly compressed, the gland nut shall 
have--
    (i) A clearance distance of \1/8\ inch or more, with no maximum, to 
travel without interference by parts other than packing; and
    (ii) A minimum of three effective threads engaged (see figures J-8, 
J-9, and J-10).
    (3) Packing nuts (see figure J-7) and stuffing boxes shall be 
secured against loosening (see figure J-11).

[[Page 63]]

    (4) Compressed packing material shall be in contact with the cable 
jacket for a length of not less than \1/2\ inch.
    (5) Requirements for lead entrances in which MSHA accepted rope 
packing material is specified, are:
    (i) Rope packing material shall be acceptable under Sec. 18.37(e) of 
this chapter.
    (ii) The width of the space for packing material shall not exceed by 
more than 50 percent the diameter or width of the uncompressed packing 
material (see figure J-12).
    (iii) The maximum diametrical clearance, using the specified 
tolerances, between the cable and the through holes in the gland parts 
adjacent to the packing (stuffing box, packing nut, hose tube, or 
bushings) shall not exceed 75 percent of the nominal diameter or width 
of the packing material (see figure J-13).
    (6) Requirements for lead entrances in which grommet packing made of 
compressible material is specified, are:
    (i) The grommet packing material shall be accepted by MSHA as flame-
resistant material under Sec. 18.37(f)(1) of this chapter.
    (ii) The diametrical clearance between the cable jacket and the 
nominal inside diameter of the grommet shall not exceed \1/16\ inch, 
based on the nominal specified diameter of the cable (see figure J-14).
    (iii) The diametrical clearance between the nominal outside diameter 
of the grommet and the inside wall of the stuffing box shall not exceed 
\1/16\ inch (see figure J-14).
    (i) Combustible gases from insulating material. (1) Insulating 
materials that give off flammable or explosive gases when decomposed 
electrically shall not be used within explosion-proof enclosures where 
the materials are subjected to destructive electrical action.
    (2) Parts coated or impregnated with insulating materials shall be 
treated to remove any combustible solvent before assembly in an 
explosion-proof enclosure.

Sec. 7.305  Critical characteristics.

    The following critical characteristics shall be inspected on each 
motor assembly to which an approval marking is affixed:
    (a) Finish, width, and planarity of surfaces that form any part of a 
flame-arresting path.
    (b) Clearances between mating parts that form flame-arresting paths.
    (c) Thickness of walls, flanges, and covers that are essential in 
maintaining the explosion-proof integrity of the enclosure.
    (d) Spacing of fastenings.
    (e) Length of thread engagement on fastenings and threaded parts 
that assure the explosion-proof integrity of the enclosure.
    (f) Use of lockwasher or equivalent with all fastenings.
    (g) Dimensions which affect compliance with the requirements for 
packing gland parts in Sec. 7.304 of this part.

Sec. 7.306  Explosion tests.

    (a) The following shall be used for conducting an explosion test:
    (1) An explosion test chamber designed and constructed to contain an 
explosive gas mixture to surround and fill the motor assembly being 
tested. The chamber must be sufficiently darkened and provide viewing 
capabilities of the flame-arresting paths to allow observation during 
testing of any discharge of flame or ignition of the explosive mixture 
surrounding the motor assembly.
    (2) A methane gas supply with at least 98 by volume per centum of 
combustible hydrocarbons, with the remainder being inert. At least 80 
percent by volume of the gas shall be methane.
    (3) Coal dust having a minimum of 22 percent dry volatile matter and 
a minimum heat constant of 11,000 moist BTU (coal containing natural bed 
moisture but not visible surface water) ground to a fineness of minus 
200 mesh U.S. Standard sieve series.
    (4) An electric spark ignition source with a minimum of 100 
millijoules of energy.
    (5) A pressure recording system that will indicate the pressure 
peaks resulting from the ignition and combustion of explosive gas 
mixtures within the enclosure being tested.
    (b) General test procedures. (1) Motor assemblies being tested 
shall--

[[Page 64]]

    (i) Be equipped with unshielded bearings regardless of the type of 
bearings specified; and
    (ii) Have all parts that do not contribute to the operation or 
assure the explosion-proof integrity of the enclosure, such as oil 
seals, grease fittings, hose conduit, cable clamps, and outer bearing 
caps (which do not house the bearings) removed from the motor assembly.
    (2) Each motor assembly shall be placed in the explosion test 
chamber and tested as follows:
    (i) The motor assembly shall be filled with and surrounded by an 
explosive mixture of the natural gas supply and air. The chamber gas 
concentrations shall be between 6.0 by volume per centum and the motor 
assembly natural gas concentration just before ignition of each test. 
Each externally visible flame-arresting path fit shall be observed for 
discharge of flames for at least two of the tests, including one with 
coal dust added.
    (ii) A single spark source is used for all testing. Pressure shall 
be measured at each end of the winding compartment simultaneously during 
all tests. Quantity and location of test holes shall permit ignition on 
each end of the winding compartment and recording of pressure on the 
same and opposite ends as the ignition.
    (iii) Motor assemblies incorporating a conduit box shall have the 
pressure in the conduit box recorded simultaneously with the other 
measured pressures during all tests. Quantity and location of test holes 
in the conduit box shall permit ignition and recording of pressure as 
required in paragraphs (c)(1) and (c)(4)(i) of this section.
    (iv) The motor assembly shall be completely purged and recharged 
with a fresh explosive gas mixture from the chamber or by injection 
after each test. The chamber shall be completely purged and recharged 
with a fresh explosive gas mixture as necessary. The oxygen level of the 
chamber gas mixture shall be no less than 18 percent by volume for 
testing. In the absence of oxygen monitoring equipment, the maximum 
number of tests conducted before purging shall be less than or equal to 
the chamber volume divided by forty times the volume occupied by the 
motor assembly.
    (c) Test procedures. (1) Eight tests at 9.4<plus-minus>0.4 percent 
methane by volume within the winding compartment shall be conducted, 
with the rotor stationary during four tests and rotating at rated speed 
(rpm) during four tests. The ignition shall be at one end of the winding 
compartment for two stationary and two rotating tests, and then switched 
to the opposite end for the remaining four tests. If a nonisolated 
conduit box is used, then two additional tests, one stationary and one 
rotating, shall be conducted with ignition in the conduit box at a point 
furthest away from the opening between the conduit box and the winding 
compartment.
    (2) Four tests at 7.0<plus-minus>0.3 percent methane by volume 
within the winding compartment shall be conducted with the rotor 
stationary, 2 ignitions at each end.
    (3) Four tests at 9.4<plus-minus>0.4 percent methane by volume plus 
coal dust shall be conducted. A quantity of coal dust equal to 0.05 
ounces per cubic foot of internal free volume of the winding compartment 
plus the nonisolated conduit box shall be introduced into each end of 
the winding compartment and nonisolated conduit box to coat the interior 
surface before conducting the first of the four tests. The coal dust 
introduced into the conduit box shall be proportional to its volume. The 
remaining coal dust shall be equally divided between the winding 
compartment ends. For two tests, one stationary and one rotating, the 
ignition shall be either in the conduit box or one end of the connected 
winding compartment, whichever produced the highest pressure in the 
previous tests. The two remaining tests, one stationary and one 
rotating, shall be conducted with the ignition in the winding 
compartment end furthest away from the conduit box.
    (4) For motor assemblies incorporating a conduit box which is 
isolated from the winding compartment by an isolating barrier the 
following additional tests shall be conducted--
    (i) For conduit boxes with an internal free volume greater than 150 
cubic inches, two ignition points shall be

[[Page 65]]

used, one as close to the geometric center of the conduit box as 
practical and the other at the furthest point away from the isolating 
barrier between the conduit box and the winding compartment. Recording 
of pressure shall be on the same and opposite sides as the ignition 
point furthest from the isolating barrier between the conduit box and 
the winding compartment. Conduit boxes with an internal free volume of 
150 cubic inches or less shall have one test hole for ignition located 
as close to the geometric center of the conduit box as practical and one 
for recording of pressure located on a side of the conduit box.
    (ii) The conduit box shall be tested separately. Six tests at 
9.4<plus-minus>0.4 percent methane by volume within the conduit box 
shall be conducted followed by two tests at 7.0<plus-minus>0.3 percent 
methane by volume. Then two tests at 9.4<plus-minus>0.4 percent methane 
by volume with a quantity of coal dust equal to 0.05 ounces per cubic 
foot of internal free volume of the conduit box and meeting the 
specifications in paragraph (c)(3) of this section shall be conducted. 
For conduit boxes with an internal free volume of more than 150 cubic 
inches, the number of tests shall be evenly divided between each 
ignition point.
    (iii) The motor assembly shall be tested following removal of the 
isolating barrier or one sectionalizing terminal (as applicable). Six 
tests at 9.4<plus-minus>0.4 percent methane by volume in the winding 
compartment and conduit box shall be conducted using three ignition 
locations. The ignition shall be at one end of the winding compartment 
for one stationary and one rotating test; the opposite end for one 
stationary and one rotating test; and at the ignition point that 
produced the highest pressure on the previous test in paragraph 
(c)(4)(ii) of this section in the conduit box for one stationary and one 
rotating test. Motor assemblies that use multiple sectionalizing 
terminals shall have one test conducted as each additional terminal is 
removed. Each of these tests shall use the rotor state and ignition 
location that produced the highest pressure in the previous tests.
    (d) A motor assembly incorporating a conduit box that is isolated 
from the winding compartment that exhibits pressures exceeding 110 psig, 
while testing during removal of any or all isolating barriers as 
specified in paragraph (c)(4) of this section, shall have a warning 
statement on the approval plate. This statement shall warn that the 
isolating barrier must be maintained to ensure the explosion-proof 
integrity of the motor assembly. A statement is not required when the 
motor assembly has withstood a static pressure of twice the maximum 
pressure recorded in the explosion tests of paragraph (c)(4) of this 
section. The static pressure test shall be conducted on the motor 
assembly with all isolating barriers removed, and in accordance with 
Sec. 7.307 of this part.
    (e) Acceptable performance. Explosion tests of a motor assembly 
shall not result in--
    (1) Discharge of flames.
    (2) Ignition of the explosive mixture surrounding the motor assembly 
in the chamber.
    (3) Development of afterburning.
    (4) Rupture of any part of the motor assembly or any panel or 
divider within the motor assembly.
    (5) Clearances, in excess of those specified in this subpart, along 
accessible flame-arresting paths, following any necessary retightening 
of fastenings.
    (6) Pressure exceeding 110 psig, except as provided in paragraph (d) 
of this section unless the motor assembly has withstood a static 
pressure of twice the maximum pressure recorded in the explosion tests 
of this section following the static pressure test procedures of 
Sec. 7.307 of this part.
    (7) Permanent deformation greater than 0.040 inches per linear foot.

Sec. 7.307  Static pressure test.

    (a) Test procedure. (1) The enclosure shall be internally 
pressurized to a minimum of 150 psig and the pressure maintained for a 
minimum of 10 seconds.
    (2) Following the pressure hold, the pressure shall be removed and 
the pressurizing agent removed from the enclosure.
    (b) Acceptable performance. (1) The enclosure during pressurization 
shall not exhibit--

[[Page 66]]

    (i) Leakage through welds or casting; or
    (ii) Rupture of any part that affects the explosion-proof integrity 
of the enclosure.
    (2) The enclosure following removal of the pressurizing agent shall 
not exhibit--
    (i) Visible cracks in welds;
    (ii) Permanent deformation exceeding 0.040 inches per linear foot; 
or
    (iii) Clearances, in excess of those specified in this subpart, 
along accessible flame-arresting paths, following any necessary 
retightening of fastenings.

Sec. 7.308  Lockwasher equivalency test.

    (a) Test procedure. (1) Each test sample shall be an assembly 
consisting of a fastening with a locking device. Each standard sample 
shall be an assembly consisting of a fastening with a lockwasher.
    (2) Five standard samples and five test samples shall be tested.
    (3) Each standard and test sample shall use a new fastening of the 
same specifications as being used on the motor assembly.
    (4) A new tapped hole shall be used for each standard and test 
sample. The hole shall be of the same specifications as used on the 
motor assembly.
    (5) Each standard and test sample shall be inserted in the tapped 
hole and continuously and uniformly tightened at a speed not to exceed 
30 rpm until the fastening's proof load is achieved. The torquing device 
shall not contact the locking device or the threaded portion of the 
fastening.
    (6) Each standard and test sample shall be engaged and disengaged 
for 15 full cycles.
    (b) Acceptable performance. The minimum torque value required to 
start removal of the fastening from the installed position (minimum 
breakway torque) for any cycle of any test sample shall be greater than 
or equal to the average breakway torque of each removal cycle of every 
standard sample.

Sec. 7.309  Approval marking.

    Each approved motor assembly shall be identified by a legible and 
permanent approval plate inscribed with the assigned MSHA approval 
number and a warning statement as specified in Sec. 7.306(d) of this 
part. The plate shall be securely attached to the motor assembly in a 
manner that does not impair any explosion-proof characteristics.

Sec. 7.310  Post-approval product audit.

    Upon request by MSHA but not more than once a year, except for 
cause, the approval holder shall make a motor assembly available for 
audit at no cost.

Sec. 7.311  Approval checklist.

    Each motor assembly bearing an MSHA approval marking shall be 
accompanied by a list of items necessary for maintenance of the motor 
assembly as approved.

[[Page 67]]

                    Appendix I to Subpart J of Part 7
[GRAPHIC] [TIFF OMITTED] TC22OC91.004


[[Page 68]]


[GRAPHIC] [TIFF OMITTED] TC22OC91.005


[[Page 69]]


[GRAPHIC] [TIFF OMITTED] TC22OC91.006


[[Page 70]]


[GRAPHIC] [TIFF OMITTED] TC22OC91.007


[[Page 71]]


[GRAPHIC] [TIFF OMITTED] TC22OC91.008


[[Page 72]]


[GRAPHIC] [TIFF OMITTED] TC22OC91.009


[[Page 73]]


[GRAPHIC] [TIFF OMITTED] TC22OC91.010


[[Page 74]]


[GRAPHIC] [TIFF OMITTED] TC22OC91.011


[[Page 75]]


[GRAPHIC] [TIFF OMITTED] TC22OC91.012


[[Page 76]]


[GRAPHIC] [TIFF OMITTED] TC22OC91.013
