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

Summary of Topics

This revision of ANSI/UL 521 dated February 28, 2023 includes flame test alignment with other detector and alarm standards; 3.12A, 3.12B, 9.6, 9.7, 47.1.1, Section 47.3, Section 47.3A and Section 47.3B.