Taking Another Path

A concerted effort to remove the term “fire” from the National Fire Alarm Code® has been underway for some time, with the results evident in the upcoming 2010 edition of NFPA 72. The reason given is that more (non-fire) emergency life-safety rules have been added—things like portable fire extinguisher monitoring and carbon monoxide detection. Even voice evacuation systems are being used for “emergency communications systems.” With so many safety functions included as features of commercial fire alarm installations, it is more consistent to state that “alarm” signals (rather than fire alarm signals) must be annunciated within 10 seconds, etc., since the rules for carbon monoxide detectors and the alarm signals they create are now also included in this standard. This is why the name has been changed to National Fire Alarm and Signaling Code®, to reflect the broader scope.

The new edition of this standard has also made a significant change to the section on wiring – excuse me – pathways. (It’s going to take me some time before I automatically refer to a circuit as a pathway). A new chapter has been created just for these interconnection rules. It is going to be named Circuits and Pathways. It is hoped that having all the wiring and fiber optic rules in one chapter will make it easier to locate information.

The good news is that the styles of circuits (A through E, 0.5 through 5, and W through Z) have been removed from the code. In the previous editions of NFPA 72, a style of circuit indicated its ability to operate under various abnormal conditions such as an open, a ground, a short, or a combination of these faults. The 2007 edition removed the style designation from the initiating device and notification appliance circuits because there were only two, Class A and Class B, and no further division was necessary. Signaling line circuits lost the bulk of Styles but kept the Style designations of 4, 6 and 7 and 6 and 7 were both Class A circuits. Starting with the 2010 edition, NFPA 72 will describe circuits and pathways using Survivability Levels 0, 1, 2, and 3, with Class designations of either A, B, C, D, E or X.

I’m sure most of you know what a Class A and Class B circuit is, but here’s a bit of a refresher. A Class A circuit will allow the connected devices to operate on both sides of a circuit with a single open while devices on a Class B pathway will only operate up to the open (fault) since a Class B circuit doesn’t have a redundant path back to the panel. Any fault that affects the designated operation of either a Class A or B circuit will cause a trouble signal at the panel. In addition to Class A and B, additional Classes of circuits have been included in the new 2010 edition. These added pathway designations are Class C, D, E and X. Like the old Style designations, these new classifications will define their intended operation for specific fault conditions.

Differentiation among the ‘classes’

A path or interconnection, with a Class C designation will be for those pathways where continued operation is verified by end-to-end communications (think ping) but the integrity of each individual pathway is not monitored.

A Class D designation will describe circuits that are not monitored for integrity but for the intended operation and will still perform its intended function if a fault occurs. These are the fail-safe circuits described in the previous editions of 72. A Class D example would be the power supply wiring to a smoke detector or relay that keeps hallway smoke doors open using magnetic door holders. In the past, these were also referred to as “self monitoring” circuits.

A path or interconnection with a Class E designation is not monitored for integrity whatsoever. These can be supplemental circuits used to operate printers, outdoor lights or any auxiliary appliances.

A Class X path or interconnection, has a redundant path back to the panel, and will continue to operate with a single open or short. This is actually better than a Class A circuit, since this will also operate properly with a short. Any fault that affects the proper operation of this X circuit will also cause a trouble signal.

Although sometimes it seems that NFPA 72 technical committees make changes from cycle to cycle just to keep us on our toes, these new pathway designations in the 2010 edition do seem to simplify as well as clarify the types of circuits we use. Stay tuned as next month I will discuss the new Survivability Levels used with Class designations to define a specific pathway.

Greg Kessinger, SET, CFPS, can be reached at Greg@firealarm.org or www.FireAlarm.org.

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