Ask the Security Alarm and Monitoring Expert

Oct. 27, 2008
Active multiplex versus digital alarm communicator transmitter

Supervision and Redundancy Requirements
What are the supervision requirements of the Active Multiplex and Digital Alarm Communicator Transmitter in regard to redundancy?

A: NFPA 72 appears to have non-equivalent requirements for different technologies. For example, Two-Way Multiplex (both wire and wireless versions), require frequent polls or check-ins in the order of every 90 seconds. The Digital Alarm Communicator Transmitter (DACT) has a 24 hour test requirement.

Why the disparity? Each technology was handled by the previous NFPA 71 and the current NFPA 72 Technical Committee on its own as a standalone system. The requirement for each technology for supervision was arrived at each in its own context and is appropriate to that technology.

Previous to the advent of Multiplex systems, supervision was constant. Two-way multiplex was a revolutionary development, allowing one control device (receiver) at a supervising station to monitor and supervise a number of premise units over multiple lines in a star arrangement. In this modern era, a newer section of NFPA 72 was created for new technologies. This section was used to list the current crop of Internet Protocol (IP) systems.

The code writers attempted to give the types of systems a measure of equivalency. But it only matters that each technology retains enough supervision to accomplish the task. The fact is, redundancy can be applied to all systems, even the higher grade Active Multiplex systems. But, you need to be careful how the redundancy is accomplished so as not to violate the listing of the product. If a product is not listed to have a redundant connection, application of a redundant path, such as a DACT, might violate the listing.

It’s advisable to check with the manufacturer on how to apply redundancy. One means might be to add redundancy as an auxiliary device. In the IP case, many listed units already have DACT on board as part of the device, even though the listing does not require its use. It would seem prudent to employ it, if a telephone line is available. Again, the caution, the service level and times required by UL and NFPA do not change with the redundant path. They must be followed as prescribed.

If the primary path were to be flipped where the DACT is assigned as the primary path, the IP path need only report once every 48 hours. With the DACT reporting once every 48 hours, the result is a signal received at the supervising station once every 24 hours. This certainly relieves the burden on the IP network of having to handle 90 second check-ins. The unit would have to be listed in this manner.

NFPA allows both paths to report simultaneously even though one path, the DACT in this example, is considered primary and the other redundant or backup. Reporting speed is not compromised. The IP signal will be annunciated at the supervising station in a fraction of a second and the DACT signal several seconds later. Ultimately, the use of a backup system using a second technology gives the user a tremendous advantage.

Louis T. Fiore is a consultant from Sparta, NJ. He is Past President of CSAA (1997-1999) and President of L.T. Fiore, Inc. His practice includes the use of wireless and the Internet for alarm monitoring, as well as regulatory issues for security systems in general. He also serves as Chairman of Central Station Alarm Association’s (CSAA) Alarm Industry Communications Committee (AICC) and Standards Committee. He is the current chairman of the SIA’s Security Industry Standards Council (SISC) and a long-time member of the Supervising Station Committee of NFPA 72. Send your questions to [email protected].