(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 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 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 VOLUME Volume 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 Minimum thickness of material for flanges and covers Minimum width of joint; all in one plane. Maximum clearance; joint all in one plane Minimum width of joint, portions of which are in different planes; cylinders or equivalent....... Maximum clearances; joint in two or more planes, cylinders or equivalent: " (a) Portion perpendicular to plane “. (b) Plane portion ... Maximum fastening " spacing; joints all in one plane. Maximum fastening spacing: joints, portions of which are in different planes .. Minimum diameter of fastening " (without regard to type of joint). Minimum thread engagement of fastening 1". Maximum diametrical clearance between fastening body and unthreaded holes through which it passes IL 12 Minimum distance from interior of enclosure to the edge of a fastening hole: 13 Joint-minimum width 1 ″. 27
" 214" 12" 0.002"
16" 3 " " 0.003"
14" 3 1/2" 1" 0.004"
+ "
45 "
+ 3¾¼"
0.008" 0.006" (16) (17) 14" 1/4"
0.008" 0.006" (16) (17) 14" 44"
0.008" 0.006" (16) (17) Y" Y /"
Yaz"
1/16"
164'
14 7/16"
