System Sensor A05-1003-002 User Manual
APPLICATIONS GUIDE
System
Smoke Detectors
1
Foreword
Studies have shown that in the United States the use of early warning fire and smoke detection systems has resulted in a significant reduction overall
in fire deaths. The sooner a fire is detected, the better the chances are for survival.
A potential problem with smoke detectors is unwanted alarms that often result in people being desensitized to the alarm system or in severe cases disconnecting the system. This is an industry-wide problem that in most cases is caused by improper application, installation and maintenance of smoke
detectors. It is hoped that the information in this guide will be used by those involved with the application, installation and maintenance of fire alarm
systems to minimize these problems.
APPLICATIONS GUIDE
System
Smoke Detectors
Contents
Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Section 1 – Standards that Apply . . . . . . . . . . . . . . . . . . . . . . . . . 2
NFPA Codes and Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Building and Fire Codes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Testing Laboratories. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Industry Publications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Manufacturer’s Publications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Section 2 – How Smoke Detectors Work . . . . . . . . . . . . . . . . . . 3
Ionization Smoke Detector Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Photoelectric Smoke Detector Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Smoke Detector Design Consideration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Considerations in Selecting Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Smoke Detectors Have Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Section 3 – Typical System Layout . . . . . . . . . . . . . . . . . . . . . . . . 5
Electrical Supervision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Class B Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Class A Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Wireless Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
General Zoning Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Fire Safety Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Smoke Detector Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Wiring Installation Guidelines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Typical Wiring Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Wireless Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Installation Do’s and Don’ts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Wiring and System Checkout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Section 4 – Proper Detector Applications,
Placement and Spacing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Where To Place Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Where Not To Place Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Special Application Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Standards for Smoke Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Detector Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
General Spacing Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Special Spacing Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Detectors in Air Handling and Air Conditioning Systems. . . . . . . . . . . . . . . . . 12
Detectors in Above-Ceiling Plenum Areas Including Plenums
Utilized as Part of the HVAC System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Section 5 – Testing, Maintenance and
Service of Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Typical Inspection, Test and Maintenance Practices . . . . . . . . . . . . . . . . . . . 13
Section 6 – Troubleshooting Techniques. . . . . . . . . . . . . . . . . . 14
What to Do About Unwanted Alarms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Reasons for Unwanted Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Maintain an Alarm Log. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Effects of Location or Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Inspect Detector for Dirt and Review Maintenance. . . . . . . . . . . . . . . . . . . . . 14
Effects of other Systems on Alarm System Wiring. . . . . . . . . . . . . . . . . . . . . . 15
Miscellaneous Causes of Unwanted Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Responsibilities of Detector Owners and Installers . . . . . . . . . . . . . . . . . . . . 15
Where to Get Help if the Source of Unwanted Alarms Can’t be Found . . . . . 16
Appendix 1 – Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . . . . 17
Appendix 2 – Alarm Log. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
NFPA Codes and Standards
NFPA publishes standards for
the proper application, installation, and maintenance of automatic smoke detectors. The
principal codes and standards that should be reviewed
before specifying or installing automatic smoke detectors
are listed below:
National Fire Protection Association (NFPA)
Batterymarch Park, Quincy, Massachusetts 02269-9101
NFPA publishes codes and standards concerning all phases of fire protection. Among those which directly concern
automatic smoke detectors are:
NFPA 70: National Electrical Code
NFPA 72: National Fire Alarm Code
NFPA 72 covers minimum performance, location, mounting, testing, and maintenance requirements of automatic
fire detectors.
NFPA 90A: Standard for the Installation of Air
Conditioning and Ventilating Systems
NFPA 92A: Smoke Control Systems in Malls, Atria, and
Large Areas
NFPA 90A and 92A provide information for the use of
smoke detectors in ducts of HVAC systems and smoke control systems.
NFPA 101: Life Safety Code
NFPA 101 specifies the requirements for smoke detection in
both new and existing buildings depending on the type of
occupancy.
Building and Fire Codes
There are three independent regional organizations which
write model building and fire codes which become law
when adopted by local and state governments. These codes
specify smoke detector requirements based on building
type and occupancy. The organizations are:
Building Officials and Code Administrators (BOCA)
4051 West Flossmoor Road, Country Club Hills, Illinois
60478-5795
BOCA’s National Building Code is generally used throughout the northeast and midwest regions of the United States.
International Conference of Building Officials (ICBO)
5360 Workman Mill Road, Whittier, California 906012298
ICBO’s Uniform Building Code is generally used throughout the West and Southwest regions of the United States.
Southern Building Code Congress International (SBCCI)
900 Montclair Road, Birmingham, Alabama 35213-1206
SBCCI’s Standard Building Code is generally used in the
South and Southeast regions of the United States.
International Code Council, Inc. (International Building
Code/International Fire Code)
5360 Workman Mill Road, Whittier, California 906012298
The organizations listed above have formed an umbrella
organization known as the International Code Council
(ICC), for the purpose of combining the codes produced by
the above three organizations into a single set of model
building and fire codes. ICC’s International Building Code
and International Fire Code were first published in 2000
and have been adopted by some states.
Testing Laboratories
Testing laboratories test smoke detectors, control panels
and other components of fire alarm systems to verify conformance with NFPA requirements and their own standards. Equipment that passes their tests are identified by a
label and/or listing.
Underwriters Laboratories, Inc. (UL)
333 Pfingsten Road, Northbrook, Illinois 60062
1655 Scott Boulevard, Santa Clara, California 95050
1285 Walt Whitman Road, Melville, New York 11747
12 Laboratory Drive, P.O. Box 13995, Research Triangle
Park, North Carolina
UL publishes an annual directory listing fire protection
equipment which bear the UL label. Its standards which
apply to smoke detectors are:
UL 217: Single and Multiple Station Smoke Detectors
UL 268: Smoke Detectors for Fire Protection Signaling
Systems
UL 268A: Smoke Detectors for Duct Applications
UL 864: Standard for Control Units for Fire Protective
Signaling Systems
Factory Mutual Research (FM)
11 51 Boston-Providence Turnpike, P.O. Box 9102,
Norwood, Massachusetts 02062
FM publishes an annual report listing fire protection equipment which bears its label.
APPLICATIONS GUIDE: SYSTEM SMOKE DETECTORS
2
The purpose of this guide is
to provide information concerning the proper application of smoke detectors used in
conjunction with fire alarm systems. It outlines basic principles that should be considered in the application of early
warning fire and smoke detection devices. Operating characteristics of detectors and environmental factors, which
may aid, delay or prevent their operation, are presented.
Fire protection engineers, mechanical and electrical engineers, fire service personnel, fire alarm designers and
Section 1
Standards That
Apply
Introduction
installers should find the contents both educational and
informative.
Though this information is based upon industry expertise
and many years of experience, it is intended to be used
only as a technical guide. The requirements of applicable
codes and standards, as well as directives of the Authorities
Having Jurisdiction (AHJ’s) should be followed. In particular, the most current version of NFPA 72 for installation
and testing of systems is a key element in the effectiveness
of smoke detection systems.
Manufacturer’s Publications
The manufacturer of the smoke detectors being used
should be contacted for any published information on their
products.
SYSTEM SENSOR
3
Industry Publications
NEMA Guide for Proper Use of Smoke Detectors in Duct
Applications
NEMA Training Manual on Fire Alarm Systems
NEMA Guide to Code Requirements for Fire Protective
Signaling and Detection Systems
NEMA Guide for proper Use of System Smoke Detectors
There are two basic types of
smoke detectors in use today;
ionization and photoelectric.
The sensing chambers of these
detectors use different principles of operation to sense the
visible or invisible particles of combustion given off in
developing fires.
Ionization Smoke Detector Operation
A typical ionization chamber consists of two electrically
charged plates and a radioactive source (typically
Americium 241) for ionizing the air between the plates.
(See Figure 1.) The radioactive source emits particles that
collide with the air molecules and dislodge their electrons.
As molecules lose electrons, they become positively
charged ions. As other molecules gain electrons, they
become negatively charged ions. Equal numbers of positive
and negative ions are created. The positively charged ions
are attracted to the negatively charged electrical plate,
while the negatively charged ions are attracted to the positively charged plate. (See Figure 2.) This creates a small
ionization current that can be measured by electronic circuitry connected to the plates (“normal” condition in the
detector).
Particles of combustion are much larger than the ionized
air molecules. As particles of combustion enter an ionization chamber, ionized air molecules collide and combine
with them. (See Figure 3.) Some particles become positively charged and some become negatively charged. As
these relatively large particles continue to combine with
many other ions, they become recombination centers, and
the total number of ionized particles in the chamber is
reduced. This reduction in the ionized particles results in a
decrease in the chamber current that is sensed by electronic circuitry monitoring the chamber. When the current
is reduced by a predetermined amount, a threshold is
crossed and “alarm” condition is established.
Changes in humidity and atmospheric pressure affect the
chamber current and create an effect similar to the effect of
particles of combustion entering the sensing chamber. To
compensate for the possible effects of humidity and pressure
changes, the dual ionization chamber was developed and
has become commonplace in the smoke detector market.
A dual-chamber detector utilizes two ionization chambers;
one is a sensing chamber that is open to the outside air.
(See Figure 4). The sensing chamber is affected by particulate matter, humidity, and atmospheric pressure. The
other is a reference chamber that is partially closed to outside air and affected only by humidity and atmospheric
pressure, because its tiny openings block the entry of larger particulate matter including particles of combustion.
Electronic circuitry monitors both chambers and compares
their outputs. If the humidity or the atmospheric pressure
changes, both chambers’ outputs are affected equally and
cancel each other. When combustion particles enter the
sensing chamber, its current decreases while the current of
the reference chamber remains unchanged. The resulting
current imbalance is detected by the electronic circuitry.
(See Figure 5.) There are a number of conditions that can
affect dual-chamber ionization sensors; dust, excessive
humidity (condensation), significant air currents, and tiny
insects can be misread as particles of combustion by the
electronic circuitry monitoring the sensors.
Section 2
How Smoke
Detectors Work
Figure 1: Particle Radiation Pattern
Figure 2: Ion Distribution
Figure 3: Ion and Particles of Combustion Distribution
Figure 5: Dual Chamber with
Particles of Combustion
Figure 4: Dual Chamber
Sensing Chamber
Source
Reference Chamber
(Current Stable)
Sensing Chamber
(Current Decreasing)
Reference
Chamber
(Current Stable)
APPLICATIONS GUIDE: SYSTEM SMOKE DETECTORS
4
Photoelectric Smoke Detector Operation
Smoke produced by a fire affects the intensity of a light
beam passing through air. The smoke can block or obscure
the beam. It can also cause the light to scatter due to reflection off the smoke particles. Photoelectric smoke detectors
are designed to sense smoke by utilizing these effects of
smoke on light.
Photoelectric Light Scattering Smoke Detector
Most photoelectric smoke detectors are of the spot type and
operate on the light scattering principle. A light-emitting
diode (LED) is beamed into an area not normally “seen” by
a photosensitive element, generally a photodiode. (See
Figure 6.) When smoke particles enter the light path, light
strikes the particles (Figure 7) and is reflected onto the photosensitive device causing the detector to respond.
Photoelectric Light Obscuration Smoke Detector
Another type of photoelectric detector, the light obscuration detector, employs a light source and a photosensitive
receiving device, such as a photodiode (see Figure 8).
When smoke particles partially block the light beam
(Figure 9), the reduction in light reaching the photosensitive device alters its output. The change in output is sensed
by the detector’s circuitry, and when the threshold is
crossed, an alarm is initiated. Obscuration type detectors
are usually of the projected beam type where the light
source spans the area to be protected.
Smoke Detector Design Considerations
Smoke detectors are based on simple concepts, but certain
design considerations need to be observed. They should
produce an alarm signal when smoke is detected, but
should minimize the impact of an unwanted signal which
can arise from a variety of causes. In an ionization detector, dust and dirt can accumulate on the radioactive source
and cause it to become more sensitive. In a photoelectric
detector, light from the light source may be reflected off the
walls of the sensing chamber and be seen by the photosensitive device when no smoke is present. The entrance of
insects, dirt, drywall dust, and other forms of contamination into the sensing chamber can also reflect light from
the light source onto the photosensitive device.
Electrical transients and some kinds of radiated energy can
affect the circuitry of both ionization and photoelectric
smoke detectors and be interpreted by the electronic circuitry to be smoke, resulting in nuisance alarms.
The allowable sensitivity ranges for both types of detectors
are established by Underwriters Laboratories, Inc. and all
are verified by their performance in fire tests. Regardless of
their principle of operation all smoke detectors are required
to respond to the same test fires.
Considerations in Selecting Detectors
The characteristics of an ionization detector make it more
suitable for detection of fast flaming fires that are characterized by combustion particles in the 0.01 to 0.4 micron
size range. Photoelectric smoke detectors are better suited
to detect slow smoldering fires that are characterized by
particulates in the 0.4 to 10.0 micron size range. Each type
of detector can detect both types of fires, but their respective response times will vary, depending on the type of fire.
Because the protected buildings normally contain a variety
of combustibles, it is often very difficult to predict what
size particulate matter will be produced by a developing
fire. The fact that different ignition sources can have different effects on a given combustible further complicates
the selection. A lighted cigarette, for example, will usually
produce a slow smoldering fire if it is dropped on a sofa or
bed. However, if the cigarette happens to fall upon a newspaper on top of a sofa or bed, the resulting fire may be
characterized more by flames than by smoldering smoke.
The innumerable combustion profiles possible with various fire loads and possible ignition sources make it difficult
to select the type of detector best suited for a particular
application.
Figure 6: Light Scattering Detector
Figure 7: Light Scattering Detector with Smoke
Figure 8: Light Obscuration Detector
Figure 9: Light Obscuration Detector with Smoke
Light Source Light Sensitive Device
Light Source Light Sensitive Device
Light Source Light Sensitive Device
Light Source Light Sensitive Device
Wiring Supervision
The initiating circuits that con-
nect smoke detectors to a con-
trol panel should be supervised so that a fault (trouble) condition that could interfere
with the proper operation of the circuit will be detected
and annunciated.
Smoke detectors are generally categorized as either 2-wire
or 4-wire detectors. Two-wire detectors derive their power
directly from the same fire alarm control panel alarm initiating device circuit over which they report an alarm.
Because of their dependency on the initiating circuit, 2-wire
detectors must be tested and listed for compatibility with
the control panel to be used, to ensure proper operation.
Four-wire detectors are powered from a separate pair of
wires, and, like the 2-wire detector, apply an electrical
short across the associated alarm initiating device circuit to
transmit an alarm (Figure 10). Because they do not derive
power from the alarm initiating device circuit, electrical
compatibility is predicated upon the operating parameters
of the power supply to which the detectors are connected
and not the initiating circuit. Supervision of the power to
4-wire detectors is mandated through the use of an end-ofline power supervision relay. When power is on, the relay
contacts of the end-of-line relay are closed and connected
in series with the end-of-line resistor beyond the last initiating device. Loss of power at any point in the power supply circuit will cause the relay to de-energize and a trouble
condition to occur on the initiating circuit.
NOTE*: Refer to the fire alarm control panel manufacturer’s
operating manual to determine the ability of a specific initiating circuit to react in a “Class B” or “Class A” fashion.
For more information, see NFPA 72-1999, paragraphs A-2-
3.6.1.2, A-2-3.6.1.1, A-2-3.6.1.2(a), and A-2-3.6.1.2(b).
NFPA 72 requirements also dictate that alarm notification
appliances (including smoke detectors with built-in
sounders) produce the 3-pulse temporal pattern fire alarm
evacuation signal described in ANSI S3.41. (Audible
Emergency Evacuation Signals)
Situations Where Other Types of Detectors May Be Used
In certain circumstances where standard smoke detectors
are unsuitable, special-purpose detectors, such as flame
detectors, heat detectors, and other detection devices may
be used.
The application of these special types of detectors should
be based on an engineering survey and used in accordance
with the manufacturer’s installation instructions provided.
Smoke Detectors Have Limitations
Smoke detectors offer the earliest possible warning of fire.
They have saved thousands of lives in the past and will
SYSTEM SENSOR
5
save more in the future. Nevertheless, smoke detectors do
have limitations. They may not provide early warning of a
fire developing on another level of a building. A first floor
detector, for example, may not detect a second floor fire.
For this reason, detectors should be located on every level
of a building. In addition, detectors may not sense a fire
developing on the other side of a closed door. In areas
where doors are usually closed, detectors should be located on both sides of the door.
As already indicated, detectors have sensing limitations.
Ionization detectors are better at detecting fast, flaming
fires than slow, smoldering fires. Photoelectric smoke
detectors sense smoldering fires better than flaming fires.
Because fires develop in different ways and are often
unpredictable in their growth, neither type of detector is
always best. A given detector may not always provide significant advance warning of fires when fire protection practices are inadequate, nor when caused by violent explosions, escaping gas, improper storage of flammable liquids
such as cleaning solvents, etc.
Section 3
Ty pical System
Layout
Class B Circuits
Class B circuits differentiate between short circuits across
the loop (alarm) and opens on the loop (trouble).
Supervision of this circuit is accomplished by passing a low
current through the installation wiring and an end-of-line
resistor. Increases or decreases in this supervisory current
are monitored by the fire alarm control panel and will
cause alarm or trouble conditions, respectively, to be indicated. A single open in a Class B circuit disables all devices
electrically beyond the open.
*NFPA 72 now classifies initiating device circuits by “Style” and “Class”. Style B
is an example of a Class B circuit; Style D is an example of a Class A circuit.
Figure 10: Two-Wire Detector Circuit
END OF LINE
RESISTOR
TYPICAL
INITIATING
DEVICES
INITIATING DEVICE
CIRCUIT
ZONE 1
TROUBLE ALARM
FIRE ALARM CONTROL UNIT
PRIMARY
POWER
SUPPLY
APPLICATIONS GUIDE: SYSTEM SMOKE DETECTORS
6
Class A Circuits
Class A circuits also differentiate between short circuits
across the loop and opens on the loop. Supervision is
accomplished by monitoring the level of current passing
through the installation wiring and the end-of-line resistor,
which in a Class A circuit is an integral part of the fire
alarm control panel. Class A wiring must return to and be
terminated in the control panel. This technique requires a
minimum of four conductors to be terminated at the panel,
and further requires that the fire alarm control panel is
designed to monitor Class A circuits. The additional circuitry necessary for Class A supervision enables the control panel to “condition” the initiating circuit to monitor
the initiating circuit from both ends when in a trouble
mode due to an open fault on the loop. This “conditioning”
ensures that all devices are capable of responding and
reporting an alarm despite a single open or non-simultaneous single ground fault on a circuit conductor.
The compatibility considerations of smoke detectors that
were detailed in Class B circuits apply with Class A as well
(Figure 11).
Figure 11: 2-Wire Detectors – Style D (Class A) Circuit
Wireless Circuits
Wireless detectors and their internal transmitters derive
their operating power from their internal battery or batteries and are listed by Underwriters Laboratories, Inc. in
accordance with requirements of NFPA 72. Supervision of
the internal battery power source is incorporated within
the smoke detector circuitry. If the battery power source
depletes to the threshold specified by Underwriters
Laboratories, the smoke detector will sound a local alert
and initiate a trouble signal once each hour for a minimum
of seven days or until the battery or batteries are replaced.
The wireless initiating devices are supervised for tamper
and/or removal by initiating a distinct trouble signal. Each
wireless device also initiates a test transmission every hour
to verify the reliability of the communication circuit. Any
device failing to communicate is identified on the control
panel no less than every four hours.
General Zoning Guidelines
The faster the source of an alarm can be pinpointed, the
faster action can be taken. Although formal rules for zoning are not given in fire protection codes, except for wireless devices where each smoke detector must be individually identified, it is always sensible to zone any system that
contains more than a small number of detectors.
Experienced detector installers and system designers recommend the following:
• Establish at least one zone on every protected floor.
• Zone natural subdivisions of a large building, such as
separate wings on a single floor.
• Minimize the number of detectors in each zone. Fewer
detectors on a zone will speed up locating the fire and
simplify troubleshooting.
• Install duct detectors in different zones than open-area
detectors for troubleshooting and locating purposes.
Fire Safety Functions
Often smoke detectors are utilized to control ancillary
equipment. Most detectors used in releasing service have
auxiliary relay contacts which are directly connected to the
system or device to be controlled. Care should be taken to
ensure that detectors utilized in such a manner are
approved for releasing service. A few of the typical applications are as follows:
•To control the flow of smoke in air handling and air
conditioning systems.
•To release doors to contain smoke in a fire situation.
•To release locks to allow exit in a fire situation.
•To capture and recall elevators in a fire situation.
•To activate a suppression system.
Spacing and placement requirements for detectors used in
releasing service may be different from detectors used in
conventional open area applications. It is recommended
that 4-wire detectors be used in these situations because
depending on the control panel and detectors used, more
than one detector relay on a circuit may not receive enough
power from the 2-wire circuit to operate during alarm.
Smoke Detector Installation
Wiring Installation Guidelines
All fire alarm system installation wiring should be installed
in compliance with Article 760 of NFPA 70, the National
Electrical Code (NEC), the manufacturer’s instructions and
the requirements of the authority having jurisdiction.
Typical Wiring Techniques
The primary rule of installation wiring is:
“Follow the Manufacturer’s Instructions”
This rule cannot be overemphasized. The requirement for
electrical supervision of the installation wires and their
connections to initiating devices makes fire alarm system
installation wiring very different than general wiring.
TYPICAL
INITIATING
DEVICES
INITIATING DEVICE
CIRCUIT
ZONE 1
TROUBLE ALARM
FIRE ALARM CONTROL UNIT
PRIMARY
POWER
SUPPLY
INITIATING DEVICE
CIRCUIT RETURN
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