Notification Appliance Circuits(Sounder)
2 NACs, Special Application
Maximum NAC Current Rating
1 Amp maximum per circuit
NAC End-of-line Resistor
10K ohms 1/2W 5%
FAULT Relay rating
2A & 30VAC, resistive
Alarm( Auxiliary ) Relay rating
2A & 30VAC, resistive
1.3 Fire Alarm System Limitations
An automatic fire alarm system – in general is made up of smoke, heat & other
detectors, manual call points, audible warning devices, fire alarm control panels with
remote notification capability, which can supply early warning of a developing fire.
Such a system, on the other hand, is unable to assure protection against property
damage or loss of life resulting from a fire.
The manufacturer recommends that smoke and/or heat detectors must be positioned
throughout a protected premise following the recommendations of the current edition
of the EN Standard, manufacturer’s recommendations contained in the Guide for
proper Use of System Smoke Detectors, which is made available at no charge to all
installing dealers. A study by the Federal Emergency Management Agency (an agency
of the United Europe) indicated that smoke detectors may not go off in as many as
35% of all fires. A fire alarm system may not provide timely or sufficient notice, or
might not function, for a diversity of reasons:
Smoke detectors may not sense fire where smoke cannot reach the detectors such as
in chimneys, in or behind walls, on roofs, or on the other side of closed doors. Smoke
detectors also may not sense a fire on another level or floor of a building. A second-
floor detector, for example, may not sense a first-floor or basement fire.
Particles or combustion or “smoke” from a developing fire may not reach the sensing
chambers of smoke detectors because:
Barriers such as closed or partially closed doors, walls, or chimneys may
inhibit particle or smoke flow.
Smoke particles may become “cold,” stratify, and not reach the ceiling or
upper walls where detectors are located.
Smoke particles may be blown away from detectors by air outlets.
Smoke particles may be drawn into air returns before reaching the detector.
The amount of “smoke” present may be insufficient to alarm the smoke detectors.
Smoke detectors are designed to alarm at various levels of smoke density. If such
density levels are not created by a developing fire at the location of detectors, the
detectors will not go into alarm. Smoke detectors, even when working properly, have
sensing limitations. Detectors that have photo electronic sensing chambers tend to
detect smoldering fires better than flaming fires, which have little visible smoke.
Detectors that have ionizing-type sensing chambers tend to detect fast-flaming fires
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