UL-844:2012 pdf free download – STANDARD FOR SAFETY Luminaires for Use in Hazardous (Classified) Locations.
11.4 Luminaires for Class I, Group A locations
11.4.1 The requirements in 11.4.2 and 11 .4.3 apply to lamp enclosures and enclosures other than lamp enclosures.
11 .4.2 Except for a conduit connection and a joint having tapered threads, a threaded joint in an enclosure shall have at least eight fully engaged threads with a Class 1 fit, at least seven with a Class 2 fit, or at least six with a Class 3 fit. See the Standard for Unified inch Screw Threads (UN and UNR Thread Form), ANSI/ASME Bi .1. A threaded joint in an enclosure having tapered threads shall fully engage at least five threads. Threads shall not be finer than 20 threads per inch (25.4 mm).
11 .4.3 A joint of the serrated type with a thread contour shall not have more than 20 serrations per inch (25.4 mm) and shall have at least five fully engaged and tightly clamped serrations.
12 Joints in Enclosures for Class II, Groups E, F, and G Locations
12.1 A joint in an enclosure shall be of the metal-to-metal, metal-to-glass, metal-to-polymeric, polymeric-to-polymeric, or polymeric-to-glass type. A joint surface shall have an arithmetical average roughness not more than 250 microinches (0.0064 mm) in accordance with the Standard for Surface Texture (Surface Roughness, Waviness, and Lay), ANSI/ASME B46.1.
12.2 The width of a joint measured from the inside of an enclosure to the outside shall not be less than 3/16 inch (4.8 mm). The clearance between the joint surfaces shall not be more than 0.002 inch (0.50 mm) for a 3/16-inch (4.8-mm) wide joint and not more than 0.003 inch (0.08 mm) for a 1/4-inch (6.4-mm) wide joint. These specified widths shall also be provided between the inside of the enclosure and the nearest edge of each bolt hole.
Exception: A luminaire with joints having both larger clearances and greater widths than those specified may be accepted for test.
12.3 If a gasket is used in a joint, it shall be formed of polytetrafluoroethylene (also see 11.1.14) or material having similar characteristics. The gasket may be of plant-fiber sheet packing material if the surface temperature to which the gasket is exposed does not exceed 90°C (194°F). The gasket material shall be mechanically attached and protected from abuse. The width of gasket contact shall not be less than 3/16 inch (4.8 mm) at all points around the joint. A gasket that is secured in a joint not intended to be opened after the luminaire is assembled is considered mechanically attached.
Exception: The gasket may be attached by an adhesive or cement if aging tests on the construction show that the means of attachment does not deteriorate. See Supplement SA.
12.4 A material that upon aging readily hardens or adheres to metal surfaces, or both, is not an acceptable gasket material. See Supplement SA for the investigation of elastomeric gaskets.
12.5 A threaded joint shall consist of at least three threads fully engaged. A screw shall not have more than 32 threads per inch (25.4 mm).