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.