UL 464A 2021 pdf download – Audible Signal Appliances for General Signaling Use.
4.2 Each terminal provided for the connection of an external antenna shall be conductively connected to the supply circuit grounded conductor. The conductive connection shall have a maximum resistance of 5.2 megohms, a minimum wattage rating of 1/2 watt, and shall be effective with the power switch in either the on or off position. Exception: The conductive connection is not required to be provided ifsuch a connection is established in the event ofelectrical breakdown ofthe antenna isolating means, the breakdown does not result in a risk of electric shock and, in a construction employing an isolating power transformer, the resistance of the conductive connection between the supplycircuit and chassis does not exceed 5.2 megohms. 4.3 The maximum value of 5.2 megohms specified in 4.2 is to include the maximum tolerance of the resistor value used; that is, a resistor rated 4.2 megohms with 20 percent tolerance or a resistor rated 4.7 megohms with a 10 percent tolerance is acceptable. A component comprised of a capacitor with a built-in shunt resistor that complies with the requirements of the Standard for Fixed Capacitors for Use in Electronic Equipment – Part 14: Sectional Specification: Fixed Capacitors for Electromagnetic Interference Suppression and Connection to the Supply Mains, UL 60384-14, may be rated a minimum of 1/4 watt. 4.4 The insertion in any socket of any vacuum tube or its glass or metal equivalent of like designation used in the product shall not result in a risk of electric shock. 5 Protection Against Corrosion 5.1 Ferrous metal parts other than bearings and similar parts where such protection is impractical, shall be protected against corrosion by enameling, galvanizing, sherardizing, plating, or other equivalent means.
6.3 Terminals or leads 6.3.1 The terminals to which wiring connections are made shall consist of binding screws with terminal plates having upturned lugs or the equivalent to hold the wires in position. Other terminal connections may be provided if found to be equivalent. 6.3.2 If a wire binding screw is employed at a field wiring terminal, the screw shall be not smaller than No. 8 (4.2 mm diameter), except that a No. 6 (3.5 mm diameter) screw may be used for the connection of a 14 AWG (2.1 mm 2 ) or smaller conductor. The screw shall thread into metal and shall be of a nonferrous metal or plated steel. 6.3.3 A terminal plate tapped for a wire binding screw shall be of metal not less than 0.050 inch (1.27 mm) thick for a No. 8 (4.2 mm diameter) or larger screw, and not less than 0.030 inch (0.76 mm) thick for a No. 6 (3.5 mm diameter) screw. The plate shall have not less than two full threads in the metal and may have the metal extruded at the tapped hole for the binding screw so as to provide two full threads. 6.3.4 A lead provided for field connections shall be not less than 6 inches (152 mm) long, provided with strain relief, and not smaller than 18 AWG (0.82 mm 2 ). The insulation, if rubber or thermoplastic, shall not be less than 1/32 inch (0.8 mm) thick.