UL 1730:2017 pdf free download – STANDARD FOR SAFETY Smoke Detector Monitors and Accessories for Individual Living Units of Multifamily Residences and Hotel/Motel Rooms.
6.3.2 A hole larger than 1-3/8 inch (34.9 mm) diameter shall have a closure of thickness not less than that required for the enclosure or shall have a standard knockout closure. Such closures shall be securely mounted.
6.3.3 A knockout in a sheet metal enclosure shall be reliably secured, but removal of the knockout shall not result in undue deformation of the enclosure.
6.3.4 A knockout shall be provided with a surrounding surface area of sufficient size to permit seating of a conduit bushing, and shall be located so that a bushing used at any knockout likely to be used during installation will not reduce spacings between uninsulated live parts and the bushing to values less than those specified in Spacings, Section 29.
6.3.5 A sheet metal member to which a wiring system is to be connected in the field shall be at least:
a) 0.032 inch (0.81 mm) thick, if of uncoated steel;
b) 0.034 inch (0.86 mm) thick, if of galvanized steel; and
c) 0.045 inch (1.14 mm) thick, if of nonferrous metal.
6.4 Nonmetallic
6.4.1 An enclosure or part of an enclosure of nonmetallic material shall have sufficient mechanical strength and durability and shall be formed so that operating parts will be protected against damage. The mechanical strength of the enclosure shall be at least equivalent to a sheet metal enclosure of the minimum thickness specified in Table 6.2.
6.4.2 Among the factors to be taken into consideration when evaluating the acceptability of a nonmetallic enclosure or parts are flammability, mechanical strength, resistance to impact, moisture absorption properties, dielectric strength, insulation resistance, resistance to arc tracking, and resistance to distortion at temperatures to which the material may be subjected under conditions of anticipated use. All these factors are to be considered with regard to aging. See the Polymeric Materials Tests, Section 38.
6.4.3 A wooden enclosure shall be solid or laminated wood, at least 3/8 inch (9.5 mm) thick with no edges exposed to internal electrical parts, and shall be spaced at least 1/2 inch (12.7 mm) from live or arcing parts and potential sources of ignition. All electrical parts shall be mounted to a metal chassis. A metal liner, at least 0.010 inch (0.25 mm) thick, shall be provided. The liner shall completely cover the bottom of the enclosure. All high-voltage circuits and nonpower-limited low-voltage circuits shall be completely enclosed by metal not less than 0.010 inch thick.
6.5.8 A transparent material other than glass may be used for the cover of an observation opening if the material does not introduce a risk of fire, distort, or become less transparent at the temperature to which it may be subjected under either normal or abnormal service conditions.
6.6 Screens and expanded metal
6.6.1 A screen and expanded metal used as a guard, enclosure, or part of an enclosure, shall comply with the requirements in 6.6.2 and 6.6.3.
6.6.2 Perforated sheet steel and sheet steel used for expanded metal mesh shall not be less than 0.042 inch (1.07 mm) thick [0.045 inch (1.14 mm) if zinc coated] if the mesh openings or perforations are 1/2 square inch (323 mm2) or less in area, and shall not be less than 0.080 inch (2.03 mm) thick [0.084 inch (2.13 mm) if zinc coated] for larger openings. The largest dimension shall not exceed 4 inches (102 mm).
Exception: If the indentation of a guard or the enclosure will not alter the clearance between uninsulated live parts and grounded metal so as to impair in tended operation of the unit or reduce spacings below the minimum required values (see Spacings, Section 29), 0.020 inch (0.51 mm) expanded metal mesh or perforated sheet metal [0.023 inch (0.58 mm) if zinc coated] may be used if.