Study Up

There have been extensive changes to the 2010 edition of NFPA 72, the National Fire Alarm and Signaling Code.

One of the more significant changes was the addition of the circuits and pathways chapter, Chapter 12. Twenty years ago, all we had to describe fire alarm circuits was Class A and B. In 1990, changes were made to replace Class A and B with styles of circuits to further describe the performance of the various circuits. Initiating device circuits were described as Styles A–E, signaling line circuits as Styles 0.5-–7 and notification appliance circuits as Styles W–Z. Because this was new, it thoroughly confused the industry. So in 1993, Class A and B were reinstated along with the styles. It stayed this way until the 2007 edition, when most of the styles were removed.

However, in that time, technology changed dramatically, and the current method of describing circuits no longer met the needs of designers and installers of fire alarm systems. As part of the remaking of NFPA 72 in 2010, a new chapter on circuits and pathways was added to better describe the methods of signal transmission for all types of circuits. Although many may think this is unnecessary, it provides a means for fire alarm system designers to describe every communications path for a fire alarm, something that the old method could not do. The old methods only described performance for initiating devices, signaling lines and notification appliance circuits. This new method does that as well, plus it describes performance for power circuits, control circuits and monitoring circuits.

In 2010, there are six classes of fire alarm pathways as well as four levels of survivability. The term “pathway” is now used to better describe all circuits as well as wireless paths or Internet connections. The definition reads, “Any circuit, conductor, optic fiber, radio carrier, or other means connecting two or more locations.”

Chapter 12 describes the installation and operation of each pathway, but does not provide requirements for when a certain pathway may be required. This information can be found in other chapters of NFPA 72 or other codes. For example, Chapter 24, Emergency Communications Systems, provides survivability requirements for pathways used for emergency voice alarm communications systems: “For systems employing relocation or partial evacuation, a Level 2 or Level 3 pathway survivability shall be required.” This will provide better direction for system designers as well as installers.

The new Class A is the same as the Class A we know from the past. Chapter 12 does a good job describing each circuit. Class A is a pathway that includes “a redundant path, operational capability continues past a single open and conditions that affect the intended operation of the path are annunciated.” Class B also is the same as the old Class B. It “does not include a redundant path, operational capability stops at a single open, and conditions that affect the intended operation of the path are annunciated.” Class C includes “one or more pathways where operational capability is verified via end-to-end communication, but the integrity of individual paths is not monitored and loss of end-to-end communication is annunciated.” A good example of this would be the circuit or pathway used for monitoring fire alarm systems. Class D is a “pathway that has fail-safe operation, where no fault is annunciated, but the intended operation is performed in the event of a pathway failure.” This would accurately describe a door-holder circuit. Class E is a “pathway that is not monitored for integrity,” such as a low-voltage power circuit. Finally, Class X includes “a redundant path, operational capability continues past a single open or short-circuit and conditions that affect the intended operation of the path are annunciated.” This would be similar to the old Style 7 circuits that were Class A with isolators to keep faulty equipment from affecting the rest of the circuit.

The four survivability levels replace the text that used to be in Chapter 6, Protected Premises. There are survivability levels 0, 1, 2 and 3. Survivability Level 0 pathways have no survivability requirements but meet the requirements of the National Electrical Code. Level 1 describes pathways installed in metal raceway in fully sprinklered buildings. Level 2 describes pathways installed using two-hour rated cables or cable systems or are installed in a two-hour rated enclosure. Level 3 combines Levels 1 and 2.

Although complicated, once the industry gets used to the new classes and survivability levels, installation requirements will become easier because designers will describe performance requirements for all circuits and pathways. Although your local jurisdiction may not have adopted the 2010 NFPA 72 yet, now is the time to start getting familiar with the new requirements.

In future issues, this column will provide information on other significant changes to NFPA 72.

HAMMERBERG is currently the president/executive director of the Automatic Fire Alarm Association Inc., headquartered in Jasper, Ga. He serves on a number of NFPA committees, including the NFPA 72 Technical Correlating Committee and the Protected Premises Technical Committee. He can be reached at

About the Author

Thomas P. Hammerberg

Life Safety Columnist
Thomas P. Hammerberg, SET, CFPS is president of Hammerberg & Associates Inc. He serves as Director of Industry Relations for the Automatic Fire Alarm Association (AFAA) Inc. and represents the association on a number of NFPA committees, including the...

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