UL 20-2021 pdf download – General-Use Snap Switches.
5.2.21 During the overload and endurance tests, all dead metal parts of the switch that are exposed to user contact, including the intended mounting surface, shall be connected through a 15 A fuse to earth ground or to the neutral (identified or grounded) conductor of the test circuit. This shall be accomplished in accordance with Clause 5.2.22. A switch shall be tested with a properly installed metal faceplate or the equivalent. 5.2.22 The fuse shall be of a type and voltage rating intended for branch-circuit protection. The potential rating of the fuse shall be equal to or greater than the maximum potential from the switch to the point at which the dead metal parts and intended mounting surface are connected. The connection shall be such that: a) On a direct-current circuit, dead metal parts are positive with respect to the nearer arcing point in the switch; and b) The potential between live parts and conductive dead metal parts is the full test potential. Note: Switches rated 250 Vthat are not marked as indicated in Clause 7.1.3 may be tested with one-halfthe test potential between live parts and conductive dead metal parts. The neutral or identified (grounded) conductor of a 125/250 V test circuitshall notbe derivedfrom a 2-wire, 250 Vcircuitbytapping offatthe midpointofresistors in series across the circuit. 5.2.23 If tests are conducted using alternating current, the circuit frequency shall be the same as the rated frequency of the switch or, if no frequency is indicated, 60 Hz alternating current shall be used. In either case, a lower frequency may be employed if agreeable to those concerned. Note: A switch rated 50 Hz shall be tested on a 60 Hz circuit, except that the currents used for the overload and endurance tests shall be 120 percentofthe currentthatwouldhave been usedhadthis switch been testedin a 50 Hz circuit.
5.3 Tungsten-Filament-Lamp Load Characteristics 5.3.1 The test circuit, including the generator or other source of supply for a switch with a tungsten- filament-lamp load rating for use on direct current, shall provide a current inrush through the switch and load of not less than eight times the normal current when the circuit is closed on a 20 A load, and the circuit shall be such that peak value of the inrush current will be reached within 1/240 of a second after the circuit is closed. If a synthetic load is employed, its characteristics shall, in addition, be such that the current-inrush factor is not less than eight times the rated current of the switch or the peak values indicated in Table 8 when tested to the corresponding current.