UL 521

Standard for Heat Detectors for Fire Protective Signaling Systems

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


  • Edition Number: 7
  • Edition Date: 02/19/1999
  • Price Code: A
  • Type: ulstd
  • ANSI Approved: 10/12/2016
  • DOD Approved: