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6.5
Location and Spacing
®
NFPA 72-2002
, 5.7.3.4.1 states: "Projected beam-type smoke detectors shall be located in accordance with the manufacturer's
documented instructions." The D296 Series Projected Beam Detectors allow for a Range (distance between the Transmitter and
Receiver) of 30 to 350 feet (9.1 to 106 meters) and a Spacing (the distance between systems) of up to 60 feet (18 meters).
On smooth ceilings, a spacing of not more than 60 ft (18.3 m) between projected beams and not more than one-half that spacing
between a projected beam and a sidewall (a wall parallel to the beam travel) should be used. Other spacing may be determined
based on ceiling height, airflow characteristics and response requirements.
In some cases, the transmitter is mounted on one end wall and the receiver is mounted on the opposite wall. It is also permitted to
mount the transmitter and receiver up to one-quarter of the spacing distance away from the end walls.
Transmitter
¼ S
Receiver
6.6
Ceilings
6.6.1 Flat Ceilings
For projected beam applications, a flat, smooth ceiling is considered to have a height of 12 ft (3.6 m) or lower, and beam or solid joist
depths of 1 ft (0.3 m) or less. Open trusses that are less than 10% material and 90% open air are not considered to affect the flow
of smoke. Smooth flat ceiling guidelines will apply where the trusses are used.
Normal spacing may be used if the projected beams are running in the direction parallel to the run of the beams or solid joists.
One-half spacing must be used if the projected beams are running at right angles to the run of the beams or solid joists.
A Joist is considered to be a support that is 4 in. (100 mm) or more in depth and 3 ft (0.9 m) or less in spacing.
A Beam is considered to be a support that is 4 in. (100 mm) or more in depth and 3 ft (0.9 m) or more in spacing.
Transmitter
Transmitter
8
½ S
S
½ S
S = Selected detector spacing
½ S
S
D296/D297 Series Application Guide
Transmitters
½ S
Ceiling beams (joists)
Receivers
Receiver
¼ S
Transmitter
Receiver
Receiver
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