What Is a Type B Fire Alarm System?

NFPA Guidelines

• The NFPA designates national requirements for the installation, maintenance, inspection and regular testing of fire alarm systems. The circuitry in specific fire alarm systems is defined by how well it performs during abnormal conditions. According to the NFPA, an abnormal condition is any situation, involving fire, where a signal or communication should be sent from the system to notify emergency services or the building owner. The multiple categories of fire alarm circuitry are made even more complicated by the inclusion of Type A and Type B fire alarm system circuits. These two classes represent differences in the ability of the circuitry to efficiently operate when exposed to conditions that may threaten the structure and effectiveness of the circuitry itself.

Type B

• Type B configurations are the most common category of fire alarm circuitry. This circuitry consists of outgoing conductors placed in the control panel that sustain peripheral devices in the fire alarm system. If the circuitry itself is compromised due, for instance, to a ground wire shorting out, the peripheral devices are unable to communicate with the main control unit. This means an alarm cannot be raised from these supporting points.

Type A

• According to John Michael Shaver, writing for the Electrical Construction and Maintenance website, Type A circuitry systems ensure a higher degree of survivability than Type B systems. A Type A system contains both outgoing conductors and return conductors at the main control panel. The main control panel circuitry supports peripheral devices downstream. Circuits journey back to the control, following the last device on the circuit. This loop configuration allows supporting devices, situated away from the threatened circuits, to report back to the main control panel.

Differences

• Contact between the main control panel and peripheral devices is not severed in Type A systems as it is with Type B systems. Type A systems can still send signals to the fire alarm panel via the returning set of conductors even if the circuitry at the main panel suffers a fault. NFPA 72 requirements also dictate that sets of conductors in the Type A category, in contrast with Class B installations, are situated in exclusive conduits that remain detached from each other at all times.