1 Scope

1.1 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.

1.2 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.

1.3 Deleted October 3, 2002

Summary of Topics

This revision of ANSI/UL 521 dated July 1, 2019 is being issued to incorporate the following changes:

Modification to Table 18.1, Heat detectors, and Table 53.1, Marking

Heat Detector Color Markings

Field Programmable Heat Detector Marking