UL 521 PDF

1 Scope

1.1 These requirements cover heat-actuated fire detectors intended for nonhazardous indoor, unconditioned areas, and outdoor locations, for use as components in automatic fire protective systems, to be installed in accordance installation in accordance with:

1. a) In Canada:

   1. 1) The National Building Code of Canada;

   2. 2) The National Fire Alarm Code of Canada;

   3. 3) The Standard for the Installation of Fire Alarm Systems, ULC-S524;

   4. 4) The Canadian Electrical Code, CSA C22.1;

2. b) In the United States:

   1. 1) The National Fire Alarm and Signaling Code, NFPA 72;

   2. 2) The National Electrical Code, NFPA 70.

1.2 These requirements cover:

1. a) Fixed-temperature detectors;

2. b) Rate-of-rise detectors;

3. c) Combination of fixed-temperature detectors and rate-of-rise detectors;

4. d) Heat Sensitive Cable; and

5. e) Heat Sensitive Tube.

Summary of Topics

This Eighth Edition of UL 521 dated December 11, 2024 has been issued to incorporate changes from proposals dated January 19, 2024, May 10, 2024, and July 12, 2024.