UL 20:2004 pdf download – General-Use Snap Switches
UL 20:2004 pdf download – General-Use Snap Switches.
4.6 InsulatIng Material
4,6.1 Insulating materials shall be judged with reference to the particular form, size, and purpose of the parts for which they are used, the manner of their assembly, and their location and security in the switch.
4.6,2 Insulating material in contact with current-carrying members shall be recognized as suitab4e for the particular app’ication. and may include certain ceramic, thernioset, thermoplastic, and elastomeric materials.
4.6.3 Vulcanized fiber may be used for insulating washers, separators, and barriers, but not for the sole support of live parts.
4.6.4 A switch intended for use in a flush-device box or on an outlet-box cover shall employ insulating materials described In Clause 4.6.5 that have been Investigated and determined to have a comparative tracking index of at least 175 V in accordance with the method for determining the comparative tracking index of solid insulating material under moist conditions, in the Standard for Polymeric Materials – Short Term Property Evaluations, UL 746A (Performance Level Category of 3 or better), or Evaluation of Properties of Po’ymeric Materials C22.2 No. 0.17.
4.6.5 The insulating materials referred to in Clause 4.6.4 are those used for the sole support of live parts, maintenance of electrical spacings, or the prevention of arcing between live parts.
4.6.6 In Canada. insulating matenals in contact with current-carrying members of switches shall have a flammability classification of V-2 or better in accordance with CSA Standard C22.2 No. 0.17, in a thickness of 1.6 mm or in the minimum thickness in contact with that current-carrying member, whichever thickness is greater.
4.6.7 In Canada. as an alternative to the requirement of Clause 4.6.6, a thermosetting material, such as phenolic. melamine. or urea may be used as an insulating material in contact with current-carrying members of switches provided that material has the following characteristics:
a) The flammability classification is HB or better in accordance with CSA Standard C22.2 No. 0.17; and
b) The relative thermal index, mechanical without impact, is a minimum of 100°C in accordance with CSA Standard C22.2 No. 0.17.
41 Actuating Members
4.7.1 Actuating members may be made of insulating material. If of metal, they shall be either insulated from current-carrying parts or covered, where otherwise exposed to personal contact, with suitable insulating material, See also Clause 4.6.2 with regard to type of insulation required.
4.7.2 An actuating member of other than thermoset insulating material shall comply with Clause 5.11.
4.8 Creepage Distances. Clearances, and Distances Through Sealing Compounds
4.8.1 Creepage distances, clearances, and distances through sealing compounds shaM not be less than the values shown in Table 6.
4.8.2 For a flush switch, a barrier boss, shoulder, recessing, or similar means may be employed to provide the minimum creepage distances and cfearances between any uninsulated live part and the wall of a flush-device box in which the switch may be mounted.
4.8.3 Compliance is checked by measurement.
4.8.4 A flush switch without integral wire leads shall be wired with the following solid copper wires connected to each terminal: No. 14, 12. and 10 AWG sizes for switches having 15 ampere (or less), 20 ampere, and 30 ampere ratings, respectively.
4.8.5 A flush switch shall be mounted in a metal gauge that simulates a flushdevice box, as shown in Figure 1.
4.8.6 External switch clearances to the box gauge’s walls are to be checked with the switch mounted in any position permitted by the mounting screws and holes.
4.8.7 A dead metal screw head, rivet, or the like shall not be considered exposed to contact by persons after the switch is installed in the intended manner, if the dead metal is located in a hole not more than 7,1 mm (9/32 inch) in diameter and recessed not less than 4.8 mm (3116 inch) in the clear.
4.8.8 In measuring a creepage distance or clearance, an isolated dead metal part interposed between uninsulated live parts of different polarity. or between an uninsulated live part and an identified (grounded) or exposed dead metal part, reduces the creepage distance or clearance by an amount equal to the dimension of the isolated dead metal part in the direction of the measurement.