Pathways to Glory
As critical as the components of a fire/life-safety system (e.g. fire alarm control panels, smoke detectors, strobes, sirens) are, they matter little if they fail to get a signal transmitted during an emergency. Thus it is essential system designers ensure uninterrupted circuit pathways, an area that has recently been updated.
This month’s fire topic is not the only thing blazing right now. It is late June as I write this and summer has arrived in a major way in my neck of the woods (Northern California) with a temperature of 105°. I am recently returned from the National Fire Protection Association’s (NFPA) annual meeting and conference, which this year was in Chicago (see sidebar). Onto our discussion this month: circuit and pathways.
This topic was added to the 2010 edition of NFPA 72 (Chapter 12) and further expanded on in the 2013 edition. This was part of the introduction of the chapter for Emergency Communications Systems (ECS) that allowed a single chapter to cover the requirements for both fire alarm and emergency communications systems. It provides information and requirements for the performance and survivability of circuits.
NFPA 72 now requires designations of circuits used within a system to be based on their performance characteristics. It is important to understand that “circuits” and “pathways” are now one in the same. Circuits are defined as a connection path between locations. Pathways are defined as any circuit, conductor, optic fiber, radio carrier or other means connecting two or more locations. As can be seen, a circuit or pathway need not necessarily be a hardwired copper pair.
Pathway survivability is defined as the ability of any conductor, optic fiber, radio carrier or other means for transmitting system information to remain operational during fire conditions.
Within Section 12.2, General, it is required that the installation of all pathway wiring, cable and equipment shall be in accordance with the NEC. Optical fiber cable shall also be installed in accordance with the NEC. Thus, in addition to being familiar with 72, the installer of a fire alarm or ECS system needs to be also familiar with the NEC, in particular Articles 760 and 770. I will cover these more in future columns.
Defining Pathway Classifications
New to NFPA 72’s 2013 edition is 22.214.171.124, which specifies that all non-power-limited and power-limited signaling system circuits entering a building shall be provided with transient protection. This would include but not be limited to conductors to sprinkler risers, post indicating valves (PIVs), OS&Y valves, tanks, outdoor radiant energy detectors and so forth, in addition to conductors between buildings or to an external annunciator.
Section 12.3 covers Pathway Class Designations. The classes are A, B, C, D, E and X.
Class A shall perform as follows: (1) It includes a redundant path. (2) Operational capability continues past a single open, and the single open fault shall result in the annunciation of a trouble signal. (3) Conditions that affect the intended operation of the path are annunciated as a trouble signal. (4) Operational capability is maintained during the application of a single ground fault. (5) A single ground condition shall result in the annunciation of a trouble signal.
Class B shall perform as follows: (1) It does not include a redundant path. (2) Operational capability stops at a single capability is maintained during the application of a single ground fault. (5) A single ground condition shall result in the annunciation of a trouble signal.
Class C shall perform as follows: (1) It includes one or more pathways where operational capability is verified via end-to-end communication, but the integrity of individual paths is not monitored. (2) A loss of end-to-end communication is annunciated.
Class D shall perform as follows: (1) Power to door holders where interruption of the power results in the door closing (2) Power to locking hardware that release upon an open circuit or fire alarm operation.
Class E is not monitored for integrity.
Class X shall perform as follows: (1) It includes a redundant path. (2) Operational capability continues past a single open, and the single open fault shall result in the annunciation of a trouble signal. (3) Operational capability continues past a single short-circuit, and the single short-circuit fault shall result in the annunciation of a trouble signal. (4) Operational capability continues past a combination open fault and ground fault. (5) Conditions that affect the intended operation of the path are annunciated as a trouble signal. (6) Operational capability is maintained during the application of a single ground fault. (7) A single ground condition shall result in the annunciation of a trouble signal.
A Class A pathway most closely matches the definition of a Class A circuit that was found in the 2007 and earlier editions of NFPA 72. A Class B pathway is a close match to the definition of a Class B circuit that was also described in the 2007 and earlier 72 documents.
Class C pathways are new, and are for those pathways that use polling or continuous communications. Supervision is accomplished through end-to-end polling.
Class D pathways are those that have a fail-safe operation, in which no fault will be communicated, but that the operation of the circuit in failure will alert occupants of an issue, such as with magnetic door holders.
A Class E pathway requires no supervision. Section 12.6 covers the types of circuits that do not require supervision in a fire alarm system (see sidebar).
The Class X pathway is new, but it describes the Class A, Style 7 Signaling Line Circuits found in past editions.
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