UL 539-2017 pdf download – Single and Multiple Station Heat Alarms.
4 Undated References 4.1 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. 5 Glossary 5.1 For the purpose of this standard the following definitions apply. 5.2 ALARM SIGNAL – An audible signal intended to indicate an emergency fire condition. 5.3 COMPONENT, LIMITED LIFE – A component that is expected to fail and be periodically replaced and whose failure is supervised. Typical examples of such components include incandescent lamps, electronic tube heaters, functional heating elements, and batteries. See also 43.4. 5.4 COMPONENT, RELIABLE – A component that is not expected to fail or be periodically replaced and is not supervised. A reliable component shall have a predicted failure rate of 2.5 or less failures per million hours. 5.5 HEAT ALARM, SINGLE STATION – A self-contained fire alarm system comprising of a heat alarm, an alarm sounding device, and a stored energy source (wound spring) incorporated in one integral package. 5.6 MECHANICALLY-OPERATED-TYPE – A heat alarm having a temperature sensitive bimetal or eutectic element and a spring-wound-type mechanism with clapper mounted within a bell housing. The snap action of the bimetal or melting of the eutectic element releases the spring mechanism resulting in a bell-type sound. 5.7 RISK OF ELECTRIC SHOCK – A risk of electric shock is determined to exist at any part, when: a) The potential between the part and earth ground or any other accessible part is more than 42.4 volt peak and b) The continuous current flow through a 1500 ohm resistor connected across the potential exceeds 0.5 milliampere.
5.9 STORY – That portion of a building included between the upper surface of a floor and upper surface of the next floor or roof above. 5.10 TROUBLE POINT – Any combination of battery voltage and series resistance that results in an audible trouble signal from a battery-operated alarm.