UL 539-2009 pdf download – Single and Multiple Station Heat Alarms.
3 Glossary 3.1 For the purpose of this standard the fllowing definitions apply. 3.2 ALARM SIGNAL – An audible signal intended to indicate an emergency fire condition. 3.3 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 41.4. 3.4 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. 3.5 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. 3.6 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. 3.7 RISK OF EL ECTRIC 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.
3.11 TROUBLE SIGNAL – A visible or audible signal intended to indicate a fault or trouble condition, such as an open or shorted condition of a component in the device or an open or ground in the connected wiring, or depletion of the supply battery. 3.12 VOLTAGE CLASSIFICATION – Unless otherwise indicated, all voltage and current values specified in this standard are rms: a) Extra-Low-Voltage Circuit – A circuit that has an AC voltage of not more than 30 volts alternating current (AC) (42.4 volts peak) and maximum power of 100 volt-amperes, such as supplied by a Class 2 transformer; or a circuit of not more than 30 volts direct current (DC) supplied by a primary battery; or a circuit supplied by a combination of a transformer and fixed impedance, that as a unit, complies with all the performance requirements of a Class 2 transformer. A circuit that is derived from a supply circuit of more than 30 volts by connecting resistance or impedance, or both, in series with the supply circuit to limit the voltage and current, is not identified as an extra-low-voltage circuit. b) Hazardous-Voltage Circuit – A circuit having characteristics in excess of those of an extra- low-voltage circuit.