UL 464A-2021 pdf free download.Audible Signal Appliances for General Signaling Use. 3.2.2 Die-cast metal for other than flush boxes is permitted when it complies with one of the alloy specifications given in Standard Specification for Zinc and Zinc-Aluminum (ZA) Alloy Foundry and Die Castings, ASTM B86. 3.2.3 Compliance of a zinc-base alloy die casting with the requirement of 3.2.2 Is to be determined by the Standard Specification for Master Alloys Used in Making Zinc Die Casting Alloys, ASTM B327. 3.2.4 If threads for the connection of conduit are tapped all the way through a hole in an enclosure wall, there shall be not less than 3-1/2 nor more than five threads in the metal, and the construction shall be such that a standard conduit bushing is capable of being attached. 3.2.5 If threads for the connection of conduit are tapped only part of the way through a hole in an enclosure wall, there shall be not less than five full threads in the metal, and there shall be a smooth, rounded inlet hole which shall afford protection to the conductors equivalent to that provided by a standard conduit bushing. 3.3 Sheet metal 3.3.1 The thickness of sheet metal employed for the enclosure or mechanism cover of an appliance shall be not less than the applicable value specified in Table 3.1. 3.3.2 At any point where conduit or metal-clad cable is to be attached, sheet metal shall be of such thickness or shall be so formed or reinforced that it has a stiffness at least equivalent to that of an uncoated flat steel sheet having a minimum thickness of 0.053 inch (1.35 mm). 3.3.3 A plate or plug closure for an unused conduit opening or other hole in the enclosure shall have a thickness not less than 0.027 inch (0.69 mm), when of ferrous metal, or 0.032 inch (0.81 mm), when of nonferrous metal for a hole having a maximum dimension not exceeding 1-3/8 inch (34.9 mm). 3.3.4 A closure for a hole larger than 1-318 inch (34.9 mm) diameter shall have a thickness equal to that required for the enclosure of the appliance. When not of such thickness, a standard knockout seal shall be used. Such plates or plugs shall be mechanically secured. 3.3.5 A knockout in a sheet metal enclosure shall be secured and shall be capable of being removed without deformation of the enclosure. 3.3.6 A knockout shall...
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