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
Contents
NFPA Journal - November/December 2013
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