11.5 Class I and II Locations – Main poles and interpoles of D.C. motors
18.104.22.168 (I, II) A d-c motor for Class I, Group D, and Class II locations, with the main poles and interpoles fastened to the stator frame by bolts or studs, shall have a distance from the edge of the pole piece to the bolt hole in the motor frame of not less than 3.2 mm (1/8 inch) if the diametrical clearance between the bolt and bolt hole is not more than 0.58 mm (0.023 inch) for a distance of not less than 12.7 mm (1/2 inch) of the unthreaded bolt shank.
22.214.171.124 (I, II) The pole piece shall be tightly clamped against the interior of the motor frame with a clearance of not more than 0.10 mm (0.004 inch).
126.96.36.199 (I, II) A lock washer may be used with the bolt. Metal shims may be provided in the joint between a pole piece and the stator frame.
11.5.2 Brush holders
188.8.131.52 (I, II) A cap of a brush holder shall be provided with metal threads for engaging a metal brush holder mounted through the wall of the motor enclosure.
184.108.40.206 (I, II) For a motor for Class I locations the number and size of engaged threads shall be as specified in Table 7, and shall have a minimum length of thread-engagement of not less than 7.9 mm (5/16 inch).
220.127.116.11 (I, II) For a motor for Class II locations, there shall be at least 3 full threads engaged, and the threads shall not be finer than 25 per 25.4 mm (1 inch).
18.104.22.168 (I, II) The insulation provided between the brush holder and the enclosure, and on the brush-holder cap, shall be phenolic composition or the equivalent, and there shall be no exposed live parts. The joints between portions of a brush-holder assembly and between the assembly and the motor enclosure shall comply with the requirements specified for joints in the motor enclosure.
12 Holes in Enclosure
12.1 (I, II) Other than as noted in 12.5, a hole in an enclosure for securing a part, such as a nameplate or a switch, shall be bottomed.
12.2 (I) The remaining thickness at the bottomed hole shall be sufficient to withstand the internal explosion pressures as shown by calculations or by an over pressure test.
12.3 (I) Fastenings such as removable bolts, screws, and studs, shall not leave an opening in the enclosure wall when omitted. The minimum thickness of metal around the hole shall be not less than 3 mm (1/8 inch) or 1/3 of the diameter of the hole, whichever is greater. The minimum thickness of metal at the bottom of the hole shall be not less than 3 mm (1/8 inch) or 1/3 of the untapped diameter, whichever is greater.
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