NFPA Journal - November/December 2013 - (Page 48)

NFPA 72 WE HAVE TO MAKE SURE the technology we're using is going to meet some minimum safety levels. That's why this process has taken at least two code cycles. to make sure fire and life safety systems are very reliable and robust," says Bunker. "We have to make sure the technology we're using is going to meet some minimum safety levels. That's why this process has taken at least two code cycles." Another concern was the reliability of an alarm system if a network goes down or is undergoing maintenance. Information technology professionals, says Moore, allow network downtime for repairs and upgrades, so safeguards need to be in place to make sure the alarm system remains operational during those periods. A separate point of contention focused on existing provisions in NFPA 72 that address performance requirements of circuits during a ground fault. Some committee members wanted networks to adhere to these code requirements, while network advocates argued that these requirements aren't necessary. Group work Addressing these concerns head-on was the goal of the Use of Networks in Fire Alarm and Emergency Communication Systems Task Group, which was formed in October 2012 and included representatives from the alarm industry, Under- 48 NFPA JOURNAL NOVEMBER/DECEMBER 2013 writers Laboratories, FM Global, and other areas. Regarding the issue of network performance during downtime and maintenance, Moore says the task group looked at various failure modes and "developed language that would give us some operational integrity and acceptable endto-end verification communication. The whole network had to provide a new level of reliability." Additional safeguards were included in a code proposal that creates a new class of circuit, Class N, which will be dedicated to networks. This new distinction would join the list of specific requirements for other types of alarm circuits and signaling pathways found in Chapter 12 of NFPA 72. For instance, a loss of communication between two endpoints on a Class N circuit will be annunciated as trouble, and a ground or short on one pathway would not impact any other pathway. Upon reviewing current code requirements for reporting a single ground fault and relating them to a network's operation, the task group decided not to include requirements for monitoring these faults. "Common fire alarm wiring connects many sensors through two parallel wires," says Horon, a task group member. "A ground [fault] at one end could short the entire communication line if a ground occurs at any point along the other wire. With that potential, you want to report that first ground as a potential problem." However, there is no need to report ground faults using Ethernet, adds Horon, since the cable prevents these events from impacting communications. Circuitry at both ends of an Ethernet cable prevents shorts or grounds from impacting the connected equipment. During its latest meeting in September, the SIGPRO Committee reviewed and approved the task group's proposals, which will make its way into the First Draft of the 2016 edition of NFPA 72. The First Draft Report posting date is March 7, 2014. "If the Class N circuit is retained through the remainder of the code development process, it will allow for newer technologies and better communication between equipment, which is where the industry is headed," says Bunker. "We as a committee need to embrace new technologies and networks ... and allow them to be used, because they can provide performance enhancements we currently don't enjoy." Fred durso, Jr. is staff writer for NFPA Journal. Photograph: Shutterstock

Table of Contents for the Digital Edition of NFPA Journal - November/December 2013

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NFPA Journal - November/December 2013