UL 917-2016 pdf download – Clock-Operated Switches.
1 Scope 1 .1 These requirements cover clock-operated switches rated 600 V or less, to be used in ordinary locations designed to close and open circuits to a load at predetermined intervals, and intended to be employed in accordance with the National Electrical Code, ANSI/NFPA 70. 1 .2 These requirements cover only clock-operated switches in which the switching contacts are actuated by a clock-work, by a gear-train, by hand, by electrically-wound spring motors, by electric clock-type motors, or by equivalent arrangements. In addition to closing and opening the switching contacts, the devices may also indicate the time of day or time interval. 1 .3 These requirements do not cover devices incorporating electronic timing circuits or switching circuits without separable contacts. 1 .4 A clock-operated switch, which is incomplete in construction features or restricted in performance capabilities, is acceptable for use as a factory-installed component provided that the restrictions established for the component are eliminated when the component is installed. 1 .5 Specific provisions are included in these requirements for TV rated clock-operated switches. 1 .6 A product that contains features, characteristics, components, materials or systems new or different from those covered by the requirements in this Standard, and that involves a risk of fire, electric shock, or injury to persons shall be evaluated using the appropriate additional component and end-product requirements as determined necessary to maintain the acceptable level of safety as originally anticipated by the intent of this Standard. A product whose features, characteristics, components, materials, or systems conflict with specific requirements or provisions of this Standard cannot be judged to comply with this Standard. Where considered appropriate, revision of requirements shall be proposed and adopted in conformance with the methods employed for development, revision, and implementation of this Standard.
5 References 5.1 Any undated reference to a code or standard appearing in the requirements of this standard shall be interpreted as referring to the latest edition of that code or standard. CONSTRUCTION 6 Frame and Enclosure 6.1 General 6.1 .1 The frame and enclosure shall be strong and rigid to resist the abuses likely to be encountered during service. The degree of structural integrity inherent in the unit shall preclude total or partial collapse with the attendant reduction of spacings, loosening or displacement of parts, and other serious defects that alone or in combination constitute an increase in the risk of fire, electric shock, or injury to persons. 6.1 .2 Electrical parts of a clock-operated switch shall be located or enclosed to reduce the risk of unintentional contact with an uninsulated live part. For the purpose of these requirements, film-coated wire is considered to be an uninsulated live part. Exception: An enclosure is not required for a device intended for assembly as part of another device. 6.1 .3 An opening in an enclosure or a clock-operated switch is acceptable if an accessibility probe as illustrated in Figure 6.1 , when inserted into the opening, cannot be made to touch any part that involves the risk of electric shock to the end-user or service personnel. However, in no case shall the opening be large enough to permit the entrance of a 1 inch (25.4 mm) diameter rod.