Why do I need two phone lines for my fire alarm system?
I need two phone lines for my fire alarm system. Is this just in case one fails, the other will work? Also, can I use one of them as my personal phone line?
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Because it’s archaic.
Yes, if you don’t have an archaic system.
Excellent question, and the requirement stems from the National Fire Code (NFPA 72) which is in effect (or some form of it) in most jurisdictions across the US. The NFPA also produces the National Life Safety Code (NFPA 101), and the national Electrical Code (NFPA 70). The Life Safety Code designates what type of building need what kind of alarm, the Fire Code designates how the alarm has to operate, and the Electrical Code designates how it has to be installed (wiring, etc.).
These codes are updated every few years, so the requirements may change at some point, but for now the Fire Code calls for two independent channels of communication to the monitoring center, one channel backing up the other. What’s more, the system needs to “auto-test” both of the channels on a regular basis (at least one channel every 24 hours), and report any regularities. This is normally only a requirement for commercial fire systems, so I suspect you have an office, restaurant, or store that is being protected.
As for using the phone line for your own use, you should check with your local fire marshal on the requirement in your jurisdiction. Chances are they do not want you to use that line for personal use, but it’s possible they will allow it. By the way, NFPA 72 now allows for alternate mean of transmission, such as long-range radio and cellular, so it does not have to be phone lines.