NFPA 72B

Abstract

This standard includes equipment and circuits for protected property which, in themselves, are insufficient for notifying the fire department in the event of fire, but which, in combination with a suitable municipal fire alarm system, are arranged to summon fire department response when operated. <br>The intent and meaning of the terms used in this standard are, unless otherwise defined herein, the same as those of NFPA 70. <em>National Electrical Code</em>&#174; <br>Municipal fire alarm systems are covered by the NFPA 1221, <em>Standard for Public Fire Service Communications.</em> <br>This standard includes three types of auxiliary alarm systems in use: <br>(a)* The local energy type [FigureA-l-1.4(a)(l) or (2)] is electrically isolated from the municipal alarm system and has its own power supply. The tripping of the transmitting device does not depend on the current in the municipal system. In a wired circuit, whether or not the alarm will be received by the municipal communication center if the municipal circuit is accidentally opened depends on the design of the transmitting device and the associated municipal communication center equipment, i.e., whether or not the municipal system is designed to receive alarms through manual or automatic ground operational facilities. In a radio box-type system, whether or not the alarm will be received by the municipal communication center depends upon the proper operation of the radio transmitting and receiving equipment. <br>(b)* The shunt type [Figure A-l-l.4(b)(l)] is electrically connected to, and is an integral part of, the municipal alarm system. A ground fault on the auxiliary circuit is a fault on the municipal circuit, and an accidental opening of the auxiliary circuit will send a needless (or false) alarm to the municipal communication center. An open circuit in the transmitting device trip coil will not be indicated either at the protected property, or at the municipal communication center; also, if a signal initiating device is operated, an alarm will not be transmitted but an open circuit indication will be given at the municipal communication center. If a municipal circuit is open when a connected shunt-type system is operated, the transmitting device will not trip until the municipal circuit returns to normal, at which time the alarm will be transmitted unless the auxiliary circuit is first returned to a normal condition. <br>A local fire alarm system made into an auxiliary fire alarm system by the addition of a relay whose coil is energized by a local power supply and whose normally closed contacts trip a shunt-type master box shall not be permitted [Figure A-l-l.4(b)(2)]. <br>(c)* A parallel telephone auxiliary alarm system [Figure A-l-l.4(c)] is a system in which alarms are transmitted over a circuit directly connected to the annunciating switchboard at the municipal communication center, and terminated at the property protected by an end-of-line resistor or equivalent. Such auxiliary systems are for connection to municipal fire alarm systems of the type in which each municipal alarm box annunciates at the municipal communication center switchboard by individual circuit. <br>The essential difference between the local energy or parallel telephone types and the shunt-type auxiliary alarm system is that accidental opening of the alarm-initiating circuits will cause an alarm on the shunt-type system only. Also, a ground on the alarm-initiating circuit of either the shunt-type or parallel telephone-type systems, respectively, extends into the municipal box wired circuit or switchboard, to which they are respectively connected, thereby grounding these circuits. If other grounds are present on the same wired circuit or at the switchboard, alarm signal transmission could be impaired or a false alarm could result. <br>This standard does not require the use of audible alarm signals other than those necessary to operate the auxiliary system. If it is desired to provide fire alarm evacuation signals in the protected property, the alarms, circuits, and controls shall comply with the provisions of NFPA 72A, <em>Standard for the Installation, Maintenance and Use of Local Protective Signaling Systems</em>, in addition to the provisions of this standard.