UL 50:2015 pdf download – Enclosures for Electrical Equipment,Non-Environmental Considerations.
8.9.2 Evaluation The enclosure shall be considered to have met the requirement if the rod cannot enter the enclosure.
8.10 Crushing resistance test
8,10.1 Three samples of equipment shall be supported on the mounting side by a fixed rigid supporting surface, in the position that is recommended by the manufacturer. Crushing force shall be applied to the exposed surfaces of the enclosure. The comp’ession force shall be applied by flat surfaces each 102 by 254 mm (4 by 10 inches). Each force appficator shall exert 445 N (100 pounds) on the sample for 1 minute, As many applicators shall be applied as the sample can accommodate, up to a maximum of 8. based upon an arrangement of applicators as indicated in Figure 10.
8.10.2 The test shall be considered successful ii at the conclusion none of the following occur;
a) Spacings are reduced below the minimum acceptable values;
b) Bare live parts or internal wiring are made accessible to contact:
C) Breakage, cracking, rupture, and the like produce an adverse effect on the insulation; and
d) Any other condition that would increase the likelihood of electiic shock or fire, or both, during use of the equipment.
8.11 Mold stress relief test
8.11.1 One representative sample of the insulating material (except for rigid thermosetting materials) assembled as intended shall be placed in a full draft circulating air oven maintained at a uniform temperature at least 10°C (50°F) hIgher than the maximum temperature of the material measured during the temperature test, but not less thai, 70°C (178°F) in any case. The sample shall remain in the oven for 7 hours. After its removal from the oven and return to room temperature, the sample shall be investigated for compliance with Clause 8.11.2.
8.11.2 Conditioning of the equipment as described in Clause 8.11.1 shall not cause softening of the material as determined by handling immediately alter the conditioning, nor shall there be any shrinkage, warpage, or other distortion, as judged after cooling to room temperature, that results in any of the following:
a) Reduction of spacings between uninsulated live parts of opposite polarity, uninsulated live parts and accessible grounded metal, uninsulated live parts and the enclosure below the
minimum acceptable values;
b) Making uninsulated live parts or internal wiring accessible to contact, or defeating the
integrity of the enclosure so that acceptable mechanical protection is not afforded to internal parts of the equipment; or
c) Causing interference with the intended operation or servicing of the equipment.
9 CabInets and Cutout Boxes
9.1 General
9.1.1 In Mexico and the United States, a cabinet or cutout box shall comply with the requirements for enclosures. However, the requirements in Clause 9.2 shall supersede equivalent requirements fOr enclosures. In Canada. this requirement does not apply.
9.2 Sheet metal cabinets
9.2.1 Notches
9.2.1 1 The front flange of each of the two side walls of a Type 1 enclosure intended for use with a panelboard may have one notch to accommodate means for installing the cover. Each notch shall not be more than 17.5 mm (11/16 inch) wide.
9.2.2 Slot and tab fastenings Slot and tab fastenings, consisting of a small cutout on the inner flange surtace and a tab created by pushing in a small segment of metal from the overlapp4ng flange, are considered as an acceptable fastening only when used in Type 1 enclosures and are used in combinahon with a rivet, weld, bolt, or screw having machine screw threads in at least one of the following locations on each length of a flange:
a) At the back edge of the enclosure, provided that the distance between the fastenings (including the slot and tab fastenings) comply with Clause or
b) Joining adjacent sides, including a top or bottom side, to comply with Clause 6,4.2.3, except that a nvet. weld, bolt or screw having machine screw threads shall be used to secure the front edge of the enclosure in accordance with Clauses and