But We've Always Done It That Way!

Technology is changing so fast these days that we could almost call this a “technology invasion.” Sometimes, it seems the technology and systems needed to accomplish the work changes in the time between one project ending and another project going out to bid. It takes a great deal of effort to keep up with these constant changes.

The codes are generally updated on a three-year cycle, and many of the new requirements appear as the result of technological shifts. Of course, now the rapid clip of technological change has outpaced the technical committee’s ability to recognize the new technology in a reasonable time frame.

Knowing this, the technical committees writing NFPA 72, National Fire Alarm and Signaling Code, addressed the issue right up front in the administration chapter by establishing an equivalency section, which states, “Nothing in this code shall prevent the use of systems, methods, devices, or appliances of equivalent or superior quality, strength, fire resistance, effectiveness, durability, and safety over those prescribed by this code.” 

Of course, a contractor that employs a new approach must submit technical justification to the authority having jurisdiction (AHJ). Once the AHJ determines the new approach provides equivalent protection, he or she must grant approval.

Most contractors’ real problem is they have not made themselves aware of technical changes to products they have used for some time, or they install their system wiring configurations without consulting the new installation manual provided with the equipment.

The outside of the device, appliance or control unit may look the same, but the manufacturer may have changed the inside operational characteristics. Also, the code may have a new requirement that will affect how you wire the system.

For example, NFPA 72 2013, Section 23.6.1 now requires that, when a single fault occurs on a pathway connected to addressable devices, the fault will not cause the loss of more than 50 addressable devices on that pathway. This requirement intends to clarify that it applies only to signaling line circuits that connect to addressable devices and not to signaling line circuits that interconnect fire alarm control units.

Fire incidents have occurred where substantial losses resulted from the shorting and failure of a signaling line circuit damaged by fire prior to the initiation of an alarm. In addition, a short circuit on a signaling line circuit—caused inadvertently as part of building operations and activities—that remains uncorrected, can result in a catastrophic failure of the fire and life safety system. If a fire occurs after the short-circuit fault condition, an alarm would not be received. 

A single short on a pathway can disable the capability of the system to initiate an alarm and, as stated in the Annex A of the code, “the alarm notification appliances and critical life safety emergency control functions including atrium smoke control, stairwell pressurization, door unlocking, and HVAC shutdown can all be disabled as well. In some configurations, even off-premises alarm, trouble, and supervisory reporting functions can be disabled.”

While we focus on the subject of cabling, know that, if you choose to install your initiating-­device circuits or signaling-line circuits in a Class A fashion, any power circuits supplying devices on those circuits must also meet the Class A requirements. Section allows for when an evaluation establishes different performance requirements and when the AHJ approves.

The annex clarifies that the paragraph’s intent is to “prevent situations where the signaling line circuit to a device is required to be one class of operation, while the power circuits, running in the same raceways and subject to the same threats, are wired to a lower class of operation. This means that it is possible to have power wiring connected to a device that is of a different class than the signaling line or initiating device circuits. One example of where meeting the same minimum performance requirements would still allow different classes of wiring is where the performance requirements are based on distance or the number of devices attached to the wires. For example, if the signaling line circuit supplies 200 devices and the performance requirement is that not more than 10 devices be lost to a wiring fault, then the class of wiring on the signaling line circuit will be Class A, with isolators to protect against shorts. Where the power wires never supply more than 10 devices, the power wires could be wired as Class B.”

Many contractors do not know this code requires the use of isolators for each circuit. Depending on the performance requirements for system operation, a contractor may need to rewire the circuits to ensure code-­compliant operation. Don’t let technology-driven code changes surprise you and decrease your profits.

About the Author

Wayne D. Moore

Fire/Life Safety Columnist
Wayne D. Moore, a licensed fire protection engineer, frequent speaker and an expert in the life safety field, is a principal member and past chair of NFPA 72, Chapter 24. Moore is a vice president with JENSEN HUGHES at the Warwick, R.I., office. He c...

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