Caught in the DACT
Phone Line Control and Integrity
It is important that the fire alarm technician do everything humanly possible to secure the telephone lines that carry alarm signals from control panel to central or supervising stations.
Section 8.6.3.2.1.1(A) stipulates that the phone service used to carry data from a fire alarm panel to monitoring station be under the control of the owner. I mention this because in multiple-tenant buildings there’s always a temptation to hitch a ride on an individual tenant’s telephone service. Unfortunately, if that tenant should leave the building, their telephone service may likely leave along with everything else they own.
Section 8.6.3.2.1.3 says that when a DACT goes off-hook, it must seize control of the phone line. To accomplish this it must be wired ahead of all the devices on the inside phone line. This is designed to assure the integrity of the connection between DACT and DACR in the event of a short circuit in an inside phone line, a problem within a telecom device, or someone already on a phone call when the panel dials out.
DACTs are typically equipped with a Form C relay that transfers the incoming phone line to the inside telecom devices. When an alarm or supervisory condition occurs, for example, this relay will route the DACT directly onto the outgoing phone line through a special phone jack that installers call a RJ31X. At the same time the inside phone line is temporarily disconnected.
The RJ31X is a series, eight-position jack designed especially for alarm systems and other equipment that must maintain total control of a phone line. They essentially contain four inputs and four outputs to which each connect through a spring-loaded switching arrangement internal to the jack. When the opposing male plug is inserted, the switch is disengaged, allowing the DACT to determine the I/O (input/output) arrangement.
Alternate Communication Means
There are a number of alternate means of communications over which an alarm control panel can communicate with the central or supervising station. Where most of them include the DACT, one or two others do not.
Cellular has become one of the most common and well accepted means of alternate communications in use today. Most of
the time it is used as a secondary means of signal transmission, whereas in others it is used as a primary means where telephone service is not practical or available.
Some of the new digital cellular systems used for fire alarm signal communications carry a UL Commercial Fire Listing.
Al Colombo is an award-winning writer who has covered electronic security and life safety since 1986. To reach Al, visit www.firenetonline.com or E-mail [email protected].
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About the Author
Al Colombo
Al Colombo is a long-time trade journalist and professional in the security and life-safety markets. His work includes more than 40 years in security and life-safety as an installer, salesman, service tech, trade journalist, project manager,and an operations manager. You can contact Colombo through TpromoCom, a consultancy agency based in Canton, Ohio, by emailing [email protected], call 330-956-9003, visit www.Tpromo.Com.
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