The ABC’s of Fire Alarm Systems - Part XII Off …

1 Page IMSA Journal2 The ABC s of fire Alarm Systems - part XIIOff-Premises TransmissionBy Anthony J. Shalna 2009 Principal IMSA Representative to the Automatic fire Alarm AssociationPresident: Southeastern Signalmen of MassachusettsRetired Approvals Manager: Gamewell-FCI by HoneywellIn previous discussions, we cov-ered various means of non-coded signaling to a central station or municipality by means of direct metallic leased telephone lines, colloquially referred to as POTS (Plain Old Telephone system ). The advent of fiber optics and micro-wave relays, together with the cu-mulative monthly costs of leasing a metallic line are making leased lines less attractive as time progresses.

2 Moreover, the gradual elimination of metallic lines will require new methods of Polarity (Remote Station)The advent of silicon diodes some years ago eliminated the major problems associated with remote station Systems at that time that relied on shorting an end of line resistor at the protected premises. Induced lightning and inadver-tent short circuits created no end of false Alarm problems. Silicon diodes made possible a different type of signaling that is completely impervious to short circuits.

3 The fire Alarm panel places DC volt-age (and current) on the phone line which is monitored at the receiv-ing station. A short or open on the lines results in loss of current that is detected as a trouble signal at the receiving station. In the event of an Alarm , the control panel at the pro-tected premises reverses the polar-ity of the DC voltage which is then detected at the station. Therefore, the system is virtually foolproof, as an Alarm can only be caused by an energized polarity reversing re-lay controlled by an energized fire Alarm control panel, and the fire department is instantly aware of any breaks or shorts in the , this method of signaling is falling into disuse for two main reasons.

4 First, a direct metallic phone line is required. The advent of microwave relays and fiber op-tics is gradually making these lines obsolete. The second disadvantage is cost. The dedicated phone line must be leased from the phone company, and these charges can accumulate considerably over a period of SignalingOne solution to this problem is the use of a Digital Alarm Communi-cator Transmitter, or DACT as it is referred to in NFPA 72, now named the National fire Alarm and Signal-ing Code. The DACT has the abil-ity of dialing a phone number and sending a digitized message to a facility equipped with a compatible Digital Alarm Communicator Re-ceiver, referred to as a DACR in the Code.

5 The DACR could be installed at a public emergency receiving sta-tion or in a Central Station where personnel will relay Alarm signals to the fire station or otherwise notify a designated service company in regard to trouble signals. DACTs are energized via various methods. Typically, a DACT some-what resembles a miniature fire Alarm control with one or more ini-tiating circuits, battery standby, etc., except it has telephone line connec-tion circuitry instead of notification appliance circuits. Short circuiting the DACT initiating circuit with a set of dry, Alarm actuated contacts from a fire Alarm control panel puts the DACT into Alarm and it makes its call to the central station.

6 Some DACTs also have a provision for direct trouble signal input, others require opening the initiating circuit via normally closed trouble actuated contacts in the fire Alarm control panel causing the DACT to send a different (trou-ble) message to the DACR. In this case, it s important to connect the trouble contacts between the Alarm contacts and end of line device, so if simultaneous Alarm and trouble signals are generated, the trouble signal will not interfere with the Alarm signal. Some DACTs feature multiple initiating circuits and have the capability of sending different digital messages to the central sta-tion, making zoned signals possible (point ID).

7 DACTs can be used in a stand-alone configuration, or may be integral (built in) with the fire Alarm control panel. A stand-alone DACT would have its own power connections, battery, etc., and be actuated by dry DACT that is integral with a fire Alarm panel obtains its operating and standby power directly from the fire Alarm control. An integral DACT is usually activated by ap-plication of an Alarm voltage onto a DACT input terminal. An outboard DACT would require shorting of one of its end of line resistors by contacts in the fire Alarm control.

8 If the DACT is integral with the fire Alarm control, supervision of the Alarm connection is not necessary, since all connections are within the cabinet. Direct application of an Alarm voltage could work with some DACTs, but care must be taken that the basic operating volt-age of both the fire Alarm control and DACT is the is required when contem-plating connection of a stand- alone Continued on page 28 Page IMSA Journal2 The ABC s of fire Alarm Systems part XII .. Continued from page 26 DACT to a fire Alarm control panel, since nothing is as simple as it seems.

9 Some years ago, fire Alarm control panel Standard ANSI/UL864 was revised by adding a power failure requirement to DACT signaling. In the event of a widespread power failure in a region, a receiving sta-tion could be inundated with DACT power failure messages. Therefore, the standard contained the require-ment that power failure messages be delayed until the standby battery capacity was reduced to a point between 50 to 75% of its normal ca-pacity. One way of doing this before microprocessor based controls came on the market, would be to use a cal-culated time delay, so that the delay would coincide with the calculation of the time required for the batteries to run down to the 50-75% point.

10 So DACTs for many years had a built-in time delay for the power failure signal. However, the fire Alarm control must have different contact outputs to differentiate between system trouble and power failure. Therefore, you cannot connect any old conventional fire Alarm control to a stand alone DACT for signaling via telephone lines, unless it s capa-ble of transmitting separate trouble and power failure signals to the DACT or unless authorized by the Authority Having Jurisdiction. A DACT integral to a microprocessor fire Alarm control would be a safe bet if it is factory engineered and listed to meet the latest standards.