Power Supply Requirements
Chapter 10 of NFPA 72 lays out the fundamental requirements that apply to virtually all fire alarm and signaling systems. One of the most critical areas is power supply requirements. Every fire alarm system must have a primary power supply (typically commercial AC power on a dedicated branch circuit) and a secondary power supply (typically storage batteries). The primary supply must not be controlled by any disconnect switch that could be inadvertently turned off. Secondary power must be capable of operating the system in a supervisory (standby) condition for a minimum of 24 hours, followed by 5 minutes of alarm operation for fire alarm systems.
Equipment Listing and Compatibility
All fire alarm equipment must be listed for the purpose for which it is used. Components from different manufacturers must be compatible and must be tested together as a system or verified by the manufacturer. This listing and compatibility requirement ensures reliable system performance and is a frequent point of emphasis in code enforcement and examination.
Circuit Designations
Chapter 10 establishes designations for signaling line circuits (SLCs), initiating device circuits (IDCs), and notification appliance circuits (NACs). Each circuit class defines the level of survivability required. Class A circuits provide redundant pathways so that a single open fault does not prevent signal transmission. Class B circuits do not provide this redundancy. Class X, Class N, and other designations address varying levels of pathway survivability.
Software, Firmware, and Documentation
Fire alarm systems that use software or firmware must meet specific requirements for program integrity and documentation. Site-specific software must be documented, and a copy must be stored at the premises or at another approved location. Changes to software must be tracked and documented to maintain system reliability and to support future troubleshooting and maintenance.
