Fire Alarm Circuits Redfined

By Wayne D. Moore | Apr 15, 2011
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Electrical contractors are familiar with the cabling installation requirements of NFPA 70 2011, the National Electrical Code (NEC), and some are familiar with the cabling requirements of NFPA 72 2010, the National Fire Alarm and Signaling Code. However, the 2010 edition of NFPA 72 has a new chapter (12) devoted to circuits and pathways.

Chapter 12 defines the characteristics of the circuits and pathways used in a fire alarm system by their performance under various adverse conditions and by their ability to survive attack from fire, known as survivability. As stated in the annex of the code, “In the 2007 edition of NFPA 72, initiating device circuit, signaling line circuit, and notification appliance circuit performance class/style tables were rooted in ‘copper’ wiring methods. Fire alarm control units use new communication technologies, such as Ethernet, fiber optics, and wireless, which do not fit in the ‘copper’ wiring methods.”

As always, contractors must install all wiring, circuits and pathways in accordance with the NEC. Thus, the new chapter appropriately references specific requirements from the NEC. These include Articles 760, 770 and 800, among several other specific paragraphs.

As NFPA 72’s annex outline: “It is important to protect the fire alarm system from lightning. One of the key requirements related to transient protection is NFPA 70, National Electrical Code, Section 760.32, which covers installation requirements. The grounding and bonding rules contained in Part IV of Article 800 are part of those installation requirements. Connections to the building grounding electrode system should be made where the circuits enter and exit a building. To minimize potential damage from induced transients, the circuits entering and exiting a building should connect to the grounding electrode system and transient protection equipment nearest the point of entry, before being intermingled with other circuits.

“NEC Section 760.32 provides references for fire alarm circuits extending beyond one building. The requirements for the installation of power-limited circuits and communications circuits are covered by Parts II, III and IV of Article 800, Communications Circuits. The methods and equipment used for providing transient protection of circuits addressed by Article 800 are not necessarily suitable for voltages expected on all fire alarm circuits.

“The requirements for the installation of non-power-limited underground outdoor circuits are found in Part I of Article 300 and the applicable sections in Part I of Article 225, Underground Branch Circuits and Feeders. Note that Article 225 does not specifically require transient protection of circuits, but it’s important to consider protecting underground circuits.

“In both power-limited and non-power-limited circuits, surge protective devices may be installed to protect against electrical surges. When installing surge protective devices, the requirements of NEC Article 285 should be followed.”

The newest code changes include the elimination of style designations for any fire alarm circuits. The code now designates circuits by class only. These designations include Class A, B, C, D, E or X, depending on the circuit’s or pathway’s performance. The technical committee has explained that it did not intend the circuit designations to create a hierarchical ranking. Rather, the designations simply provide guidance on the levels of performance and survivability.

For example, a pathway designated as Class A will include a redundant path. Its operational capability will continue past a single open. And any conditions that affect the intended operation of the path will be annunciated.

The code provides a new Class X designation to ensure additional performance requirements. A Class X pathway will include a redundant path. Its operational capability will continue past a single open or short-circuit. And, any conditions that affect the intended operation of the path will be annunciated. The Class X pathway designation intends to define those performance characteristics of what previous editions of the code defined as a “Style 7 signaling line circuit.” Addressable fire alarm systems frequently use this type of circuit. Previous editions of the code described the Class A signaling line circuit as a “Style 6 signaling line circuit.”

A Class B pathway designation indicates the pathway does not include a redundant path. Its operational capability stops at a single open. And any conditions that affect the intended operation of the path will be annunciated.

The new Class C pathway designation includes one or more pathways where end-to-end communication verifies operation integrity. But, the integrity of individual paths is not monitored, and a loss of end-to-end communication is annunciated.

As the annex of the code states, the Class C reference “is intended to describe technologies that supervise the communication pathway by polling or continuous communication ‘handshaking’ such as the following:

“(1) Fire control unit or supervisory station connections to a wired LAN, WAN, or Internet

“(2) Fire control unit or supervisory station connections to a wireless LAN, WAN, and Internet

“(3) Fire control unit or supervisory station connections to a wireless (proprietary communications)

“(4) Fire control unit digital alarm communication transmitter or supervisory station digital alarm communication receiver connections to the public switched telephone network”

The Class D reference describes pathways that have a fail-safe operation that performs the intended function when the connection is lost, but Class D pathways do not have supervision of the integrity of the pathway. The most common circuit that you use in a fire alarm system that meets this designation would include the wiring that provides power to door holders. Interruption of the power results in the door closing.

And finally, the Class E designation intends to describe pathways that do not require monitoring for integrity or electrical supervision.

The second part of Chapter 12 describes the survivability of circuits. Survivability requirements of certain communications circuits have existed for more than 30 years. Sadly, designers, authorities having jurisdiction and installers have often gravely misunderstood these requirements. Chapter 3 of the code does not include a definition for “survivability.” However, Chapter 23, Section 23.10.2, states in part, “Fire alarm systems used for partial evacuation and relocation shall be designed and installed such that attack by fire within an evacuation signaling zone shall not impair control and operation of the notification appliances outside the evacuation signaling zone.”

This section provides the performance description of survivability. Designers, authorities having jurisdiction and contractors should also design and install the circuits controlling notification appliance circuits and equipment, which operate in common with more than one evacuation signaling zone—in a way that the fire will not disable them.

Note that Chapter 12 does not require survivability. It simply describes the level designations. Chapter 24 contains the requirements for survivability. Chapter 24 also includes references to Chapter 12’s descriptions of the different levels of survivability. Each level of pathway survivability offers options for the designer and installer to meet the requirements. Some users of the code have been confused and assumed that, if a contractor installed a circuit in conduit, that circuit would have survivability. Wire or cable in a raceway, such as conduit, certainly has mechanical protection, but the conduit or raceway cannot preserve the integrity of circuits when attacked by fire.

The “levels” of survivability described in Chapter 12 include level 0, 1, 2 and 3. Essentially, Level 0 pathways have no required survivability. Level 1 pathways include those installed in buildings fully protected by automatic sprinkler systems in accordance with NFPA 13, Standard for the Installation of Sprinkler Systems, with any interconnecting conductors, cables or other physical pathways installed in metal raceways.
Pathway survivability Level 2 consists of one or more of the following:

“(1) 2-hour fire-rated circuit integrity (CI) cable

“(2) 2-hour fire-rated cable system [electrical circuit protective system(s)]

“(3) 2-hour fire-rated enclosure or protected area

“(4) 2-hour performance alternatives approved by the authority having jurisdiction”

Pathway survivability Level 3 is identical to Level 2, except the pathways include those installed in buildings fully protected by automatic sprinkler systems in accordance with NFPA 13, Standard for the Installation of Sprinkler Systems.

Contractors will install most circuits in nonvoice fire alarm systems with a Level 0 or Level 1 survivability designation. Generally speaking, contractors will use pathway survivability of Level 2 or 3 for in-building fire emergency voice/alarm communications where the occupants will either be partially evacuated or relocated to a non-fire area within a building.

As the new code becomes the preference, design drawings will designate the pathways to identify the properties of the system interconnections and survivability requirements.

Based on the number of states already adopting NFPA 72 2010, the contractor must understand these new circuit, cable and pathway designations for fire alarm systems.

MOORE, a licensed fire protection engineer, frequent speaker and an expert in the life safety field, is a past chair of the NFPA 72 Technical Correlating Committee. Moore is a principal with Hughes Associates, Inc. at the Warwick, R.I., office. He can be reached at [email protected].

About The Author

MOORE, a licensed fire protection engineer, was a principal member and chair of NFPA 72, Chapter 24, NFPA 909 and NFPA 914. He is president of the Fire Protection Alliance in Jamestown, R.I. Reach him at [email protected]





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