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UL 521 1999 Edition, February 19, 1999
Complete Document
UL Standard for Safety Heat Detectors for Fire Protective Signaling Systems
Published By:UL (UL)
Page Count:80
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These requirements cover heat detectors for fire protective signaling systems intended to be installed in ordinary indoor and outdoor locations in accordance with the Standard for Automatic Fire Detectors, NFPA 72E.

Heat detectors covered by these requirements employ either normally open contacts or normally closed contacts, provide an electronic signal, or consist of a heat-sensitive cable. The requirements do not cover heat detectors for journal-alarm or unit-alarm devices.

A product that contains features, characteristics, components, materials, or systems new or different from those in use when the standard was developed, 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 level of safety for the user of the product as originally anticipated by the intent of this standard.