In the day-to-day challenges of electrical contracting, when a specific wiring question arises, the wiring methods you use depend on what you have learned in the trade along with an occasional dose of the National Electrical Code. Most of you know that when it comes time to install a fire-alarm system, you should refer to NEC Article 760 to determine what wiring methods are needed.
Many electrical contractors assume the NEC contains all the information they need to install fire-alarm system wiring. Unfortunately that assumption will prove wrong, for two reasons. First, NFPA 72-2002, National Fire Alarm Code (NFAC), has additional requirements in chapters 4 and 6 that apply to fire-alarm system wiring. Second, a contractor should always check with the fire official in the building’s jurisdiction before beginning installation. Many jurisdictions have developed their own additional installation requirements.
Chapter 4 of the NFAC, specifically Section 4.4.7, has requirements relating to monitoring the circuit-wiring integrity. In the past, various standards referred to this as “electrical supervision.” The method used to monitor the fire-alarm circuits for integrity will depend on the system’s technology. Typical zoned or “conventional” systems monitor the initiating-device circuits, signaling-line circuits and notification-appliance circuits differently than point-identification or “addressable” systems. This monitoring for integrity will report a “trouble signal” to the fire-alarm system control unit if one of the conductors breaks or becomes grounded.
NFAC Section 6.4.2 begins the discussion of “Circuit Designations” stating that, “Initiating-device circuits, notification-appliance circuits, and signaling-line circuits shall be designated by class or style, or both, depending on the circuit’s capability to continue to operate during specified fault conditions.”
In addition to installing fire-alarm circuits in accordance with the NEC, contractors must understand that fire-alarm system wiring has class and style.
As it turns out, the NFAC only classifies circuits as A or B. Both provide monitoring for integrity. Class A circuits will continue to operate even with a single break or ground fault.
The NFAC describes five initiating-device circuits styles, 10 signaling-line circuits styles and four notification-appliance circuits styles. Who chooses the class and style of fire alarm circuits? Except for those jurisdictions that have incorporated a specific class or style requirement into their regulations, the fire-alarm-system designer must choose the class or style of circuit for a particular installation.
But, as a contractor, what about your job as the installer of these fire-alarm circuits? What is really important to you? You need to understand that a circuit’s class and style designation help define the wiring methods needed to install the system. If the designer has chosen to use a Class A circuit, the conductors must leave and return to the fire-alarm system control unit with no “T-taps” allowed. Class B circuits must extend from the fire-alarm system control unit to the last device or appliance on the circuit, and then terminate in an end-of-line device. For conventional zoned systems, this end-of-line device will most often consist of a resistor to complete the circuit.
When installing initiating-device circuits for conventional-type systems designated as Styles A, B or C, signaling-line circuits for addressable-type systems designated as Styles .5, 1, 3, 3.5, 4 or 4.5, or notification-appliance circuits designated as Styles W, X or Y, install these as you would Class B circuits. When installing initiating-device circuits designated as Styles D or E, signaling-line circuits designated as Styles 2, 5, 6 or 7, and notification appliance circuits designated as Style Z, install these as you would Class A circuits.
Obviously, you will need to own a copy of the National Fire Alarm Code. Place it on the shelf next to your NEC. Always use both documents when installing a fire-alarm system.
Everything electrical contractors do contributes to the safety and welfare of the people using the buildings they work on. Ensure these people remain safe by understanding all the NEC and the NFAC requirements. EC
MOORE, a licensed fire protection engineer, frequent speaker and an expert in the life safety field, is a co-editor of the current National Fire Alarm Code Handbook. Moore is a principal with Hughes Associates Inc. at the Warwick, R.I., office.