UL 353:2011 pdf download – Limit Controls.
6.3.1 Doors or covers shall be provided with means for securing them to the enclosure
6.3.2 Sheet metal screws threading directly into metal brackets or enclosure walls shall not be used for
attachment of covers, or doors which have to be removed for installation or operation of the equipment.
They may thread into spring steel nuts permanently held in place and protected against corrosion.
Machine screws and self-tapping machine screws may thread directly into sheet-metal walls.
6.3.3 A snap-on cover which gives access to bare live parts and which does not require a tool for removal shall withstand the following tests:
a) A cover, which can be removed with one hand, shall not be released when a squeezing force of 14 pounds (62.3 N) is applied at any two points. the distance between which shall not exceed 5 inches (127 mm), as measured by a tape stretched tightly over that portion of the surface of the cover which would be encompassed by the palm of the hand. The test shall be performed before and after ten removal and replacement operations;
b) A cover shall not become disengaged troni the case when a crect pull of 14 pounds (62.3 N) is applied. Faa’ this test, the cover Is to be gripped at any two convenient points. The test shall be performed before and after ten removal and replacement operations; and
C) A cover shall be capable of withstanding an impact force of 1 foot-pound (0.138 kg-rn) applied to the accessible faces of the cover (one blow per face) without being displaced. The radius of the ball used for this test shall be not less than 1 inch (25.4 mm).
6.3.4 All nonmetallic covers which give access to bare live parts shall comply with the requirements in
6.3.3 with the cover screws tightened, and with the cover screws loosened one full turn.
6.3.5 An enclosure cover shall be hinged if it gives access to fuses, thermal Cutouts, or any protective device, the normal functioning of which requires renewal or resetting, or if it is necessary to open the cover in connection with the normal operation of the control.
6.3.6 A door or cover giving access to fuses or thermal cutouts in other than low-voltage circuits shall shut against a 1/4 inch (6.4 mm) rabbet, or the equivalent, or shall have either turned flanges for the full length of four edges or angle strips fastened to it. Flanges or angle strips shall fit closely with the outside of the walls of the box and shall overlap the edges of the box not less than 1/2 inch (12.7 mm). A construction which affords equivalent protection or a combination of flange and rabbet is acceptable.
6.3.7 Strips used to provide rabbets or angle strips fastened to the edges of a door shall be secured at not less than two points, not more than 1-1/2 inches (38.1 mm) from each end of each strip and at points between these end fastenings not more than 6 inches (152.4 mm) apart.
6.3.8 A hinged cover shall not depend solely upon screws or other similar means requiring the use of a tool to hold it closed but shall be provided with a catch or spring latch; except that if a hinged cover Is provided, although not required, a hasp, sliding latch, or other means for holding the cover closed may be employed.
6.3.9 No wires other than those leading to a part mounted on the door or cover or those of a low-voltage nonsafety circuit shall be brought out through the door or cover of an enclosure.
6.3.10 lf low-voltage nonsafety wiring is brought out through the door or cover,the construction shallconform with 9.1.15 and 20.1.3.Also, the construction shall be such that the wires are not subject to strainor mechanical injury when the door is opened as the cover is removed.