Managing Cable Needs: The Key to Communications System Installation

Managing Cable Needs Photo Credit: Shutterstock / MikroKon
Photo Credit: Shutterstock / MikroKon

As I have often written, NFPA 72, National Fire Alarm and Signaling Code, is not the only code you must follow when designing and installing a fire alarm or emergency communications system. In addition to the building codes and the Life Safety Code, you must install the wire and cable for all systems in accordance with NFPA 70, National Electrical Code (NEC).

Section 12.2.3.2 requires you to install fire alarm system wiring and equipment, including all circuits the fire alarm system controls and powers, in accordance with NFPA 72 and NEC Article 760 requirements. This includes the wiring for all fire detection and alarm-initiating devices, such as guard’s tour, sprinkler waterflow and sprinkler supervisory systems, and the wiring for all alarm, supervisory and trouble notification appliances. It also includes all circuits controlled and powered by the fire alarm system for the control of other building systems’ safety functions, elevator capture, elevator shutdown, door release, smoke doors and damper control, fire doors and damper control, and fan shutdown. Please note that, again, these requirements only apply where these circuits receive power from and control by the fire alarm system.

NFPA 72 devotes a chapter to circuits and pathways, and it specifies the performance requirements of the wiring scheme planned for the fire alarm or emergency communications system. This chapter provides a good place to start this discussion regarding cable management for these systems.

Chapter 12 also includes the required performance depending on their designation as Class A, B, C, D, E, N or X. The designer must choose the class of circuit, and as stated previously, the installation requirements of the wiring and cable used for a certain designated circuit must meet NEC Article 760 requirements.

If your design specifies survivability when exposed to a fire for certain circuits, you will need to determine how that performance requirement affects your cable management. To meet this survivability requirement, you will need to install some form of two-hour-rated cable or specify a performance alternative using the building construction.

The scope of Article 760 states that it covers fire alarm system wiring and equipment installation, including all circuits the fire alarm system controls and powers. As you formulate your design, be aware if special conditions within a jurisdiction require a specific class of circuit. For example, if you planned to install all cable in a Class B format and the local jurisdiction (or the owner) demanded Class A, the cable costs will become close to double that of your planned Class B installation.

Article 760 classifies all fire alarm circuits as either nonpower- limited or power-limited. The power output of the various circuits supplied by a fire alarm control unit will determine the type of circuits available. The listing of that control unit by a nationally recognized testing laboratory will verify the power output. Based on this verification, the instruction manual or marking inside the control unit will state the proper classification of circuit to use for each of the control unit’s circuits. If you cannot determine whether the outputs are power limited, the default is nonpower-limited.

The NEC specifies particular wiring methods for each circuit classification. The NEC treats power-limited circuits as somewhat safer by circuit design and provides more flexibility in the cable installation. For example, you may install power-limited cables above suspended ceilings without the need for raceway protection.

Power-limited and nonpower-limited fire alarm cables installed in ducts, plenums or other spaces used for environmental air must comply with Section 300.22 of the NEC . This article applies to the installation and uses of electrical wiring and equipment in ducts used for dust, loose stock or vapor removal; ducts specifically fabricated for environmental air; and other spaces used for environmental air (normally called plenums). Of course, the NEC requires all wiring to be protected from physical damage, regardless of its designation.

Managing the wiring and cable of each fire alarm or emergency communications system is especially important when dealing with circuits that consume greater amounts of power, such as notification appliance circuits. A common mistake is when an installer plans a system’s cable needs based on the exact design and specifications for a project’s required notification appliances. As a designer or installer, account for the possible need for additional notification appliances to comply with the code-required visibility or audibility. In addition, consider possible future expansion of the building covered by the system where you will need to install additional notification appliances. Size your circuits to ensure the system’s capability for expansion.

To ensure intelligibility of the voice reproduction notification appliances in an emergency communications system, you may need to include more speakers than originally intended. When that happens, your success at managing the cable installation will be evident.

Managing the cable installation for a fire alarm or emergency communications system is a very important step in the design and installation process. Paying attention to cabling requirements is essential to ensure your success for a code-compliant and reliably operating fire alarm or emergency communications system.

Additionally, managing cable installation for the increased number of fire safety functions that the fire alarm system operates or controls may prove challenging. To capably manage the cable needed for these functions, you must fully understand the system operation in each of the major states: alarm, supervisory and trouble conditions. Understand how these conditions will operate or interface with the fire safety functions.

In many cases, requirements will lead you to interface with these fire safety functions without requiring testing for the correct operation, unless the jurisdiction has adopted NFPA 4, Standard for Integrated Fire Protection and Life Safety System Testing. Regardless, plan to test all integrated functions to ensure you have managed the cable installation and connections properly.

Proper cable management, from design through installation, relates to all new and existing systems you may design and install. If a customer asks you to replace or upgrade an existing fire alarm system, understand that the NEC requires the removal of unused cables. The NEC addresses removal of electrical equipment in addition to the removal of abandoned conductors. Abandoned conductors and cables from several generations of equipment can increase the fire loading unnecessarily in a building. Not surprisingly, you find abandoned cable wherever an upgrade has occurred to fire alarm systems, communications systems or computer networks. Several sections in the NEC specify where you must remove abandoned cable. The NEC defines abandoned fire alarm cable as “installed fire alarm cable that is not terminated at equipment other than a connector and not identified for future use with a tag.”

Article 760.25 states, “The accessible portion of abandoned fire alarm cables shall be removed. Where cables are identified for future use with a tag, the tag shall be of sufficient durability to withstand the environment involved.”

Also, the NEC defines accessibility (as applied to wiring methods), as wiring that is “capable of being removed or exposed without damaging the building structure or finish or not permanently closed in by the structure or finish of the building.”

Managing the cable installation for a fire alarm or emergency communications system is a very important step in the design and installation process. Paying attention to cabling requirements is essential to ensure success for a code-compliant and reliably operating fire alarm or emergency communications system.

As we have discussed before, paying attention to detail in the design and installation of fire alarm or emergency communications systems will help to ensure a quick acceptance of the installed system by the authority having jurisdiction. All of the above, including successful cable management for your fire alarm or emergency communications systems installations, will increase profitability in the systems market.

About the Author

Wayne D. Moore

Fire/Life Safety Columnist

Wayne D. Moore, a licensed fire protection engineer, frequent speaker and expert in the life safety field, is a principal member and past chair of NFPA 72, Chapter 24. He is a vice president with Jensen Hughes at the Warwick, R.I., office and can be...

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