Bosch D256A Specsheet
Fire Alarm Systems | D256A Fixed-temperature (135°F [57°C]), Rate-of-Rise Heat Detector Head
D256A Fixed-temperature (135°F [57°C]),
Rate-of-Rise Heat Detector Head
www.boschsecurity.com
u Mounts on low‑profile six‑inch diameter base
u Easy head removal for cleaning and servicing
Use these detectors for indoor confined areas where
high heat‑output fires are expected, or in areas where
ambient conditions do not allow the use of other
detection methods.
Notice
These heat detectors are intended for detection
circuits that protect property. Use smoke
detectors to protect personnel.
Use the D256A (response-rated at 135°F [57°C]) in
areas where the ambient temperatures do not exceed
120°F (49°C).
Functions
u Available in 24 VDC, 135°F (57°C) or 190°F (88°C)
fixed settings
u Dual built-in power and alarm LEDs viewable from
360°
u Highly stable operation and RF/Transient protection
reaches its fixed temperature value or when the
temperature rises more than 12°F (6.6°C) in less than
a minute. When an alarm signal is sent, the red alarm
LEDs latch on.
The thermistor heat element used in the detector is
protected from damage by the built‑in, durable plastic
guard.
Certifications and approvals
Region Certification
USA UL UQGS_S4990 - Heat-automatic Fire De-
tectors
CSFM see our website
Detector Head and Base System
These heat detectors have two components: the
detector base and the detector head. The bases are
permanently attached and wired to back boxes. The
interchangeable heads quickly detach for replacement
and cleaning without affecting the circuit wiring.
Detection Method
The heat detectors performs the same function as a
mechanical heat sensing device, but with electronic
precision. The detector sends an alarm signal when it
Installation/configuration notes
Compatible Products
The following products are compatible with the heat
detector heads:
Category Products
Control
Panels
D7022 Conventional Fire Alarm Control Panel
D7024 Conventional and Addressable Fire Alarm
Control Panels
2 | D256A Fixed-temperature (135°F [57°C]), Rate-of-Rise Heat Detector Head
Category Products
FPD-7024 Conventional and Addressable Fire Alarm
Control Panels
D9124 Addressable Fire Alarm Control Panel
D9412, D7412, D7212 Control Panels
G Series Control Panels
1
D9112 Addressable Control Panel
Detector
Bases
D250A Two‑wire Detector Base (12 VDC or 24 VDC)
D280A Two‑wire Detector Base (24 VDC)
D290 Four‑wire Detector Base (24 VDC)
D291 Series Detector Bases
1
G Series = D9412G, D7412G, D7212G, D9412GV2, D7412GV2,
2
D7212GV2, D9412GV3, D7412GV3, D7212GV3, D9412GV4,
D7412GV4, and D7212GV4
2
D291 Series = D291MMaster Addressable Detector Base (24 V) and
D291S Addressable Detector Base (24 V)
Notice
These heat detectors do not operate on standard
12 VDC two‑wire loops; they require 24 VDC.
When used with 12 VDC control panels, a UL
Listed 24 VDC auxiliary power supply is required.
Environmental
Temperature
+32°F to +120°F (0°C to +49°C)
(ambient):
Note: The normal environment where these detectors are installed
should be within the specified ambient temperature limits.
Mechanical
Color: Bone white
Dimensions
6 in. x 2 in. (15.2 cm x 5 cm)
(diameter x D):
Ordering information
D256A Fixed-temperature (135°F [57°C]), Rate-of-Rise
Heat Detector Head
Fixed‑temperature (135°F [57°C]), rate‑of‑rise
mechanical heat detector head for use in 12 VDC or
24 VDC nominal circuits; requires a base.
Order number D256A
Mounting
The detector base installs over a back box and
contains all the wiring. The detector head attaches to
the base by hand by aligning the head with the base
and turning it clockwise. No tools are required for
installation other than the hex key used to tighten the
tamper screw.
Wiring
Refer to the installation instructions for the specific
base for detailed wiring requirements.
Parts included
Quant. Component
1 Detector head
1 Literature pack
Technical specifications
Electrical
Current (alarm): 150 mA at 24 VDC
Current
0.04 mA at 24 VDC
(supervisory):
Current (surge): 0.160 mA at 24 VDC
Voltage (operating): 15.0 VDC to 33.0 VDC
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