Data Sheet for Product

Siemens
Smart Infrastructure - Building Products
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usa.siemens.com/fire
Installation
All Model OH921 detectors use a surface-mounting base, Model DB-11 or Model DB-11E, which mounts on a
4-inch (10.2 cm.) octagonal, square or single-gang electrical box. The base utilizes screw-clamp contacts for
electrical connections and self-wiping contacts for increased reliability.
The Model DB-11 detector base can be used with the optional Siemens Model LK-11 detector locking kit, which contains 50
detector locks and an installation tool to prevent unauthorized removal of the detector head.
Model DB-11 has aesthetically conducive plugs to cover the outer mounting-screw holes.
Model OH921 may be installed on the same initiating circuit with the following [when used with Cerberus PRO Modular |
Model FC9-series | FireFinder XLS/V FACPs] –
• XTRI Series interface modules
• HFP-11, HFPT-11 detection devices
• HTRI series interface modules
• HCP output control modules
• HMS & XMS series manual stations
• HZM conventional zone module
Each detector is shipped with a protective dust cover, consists of the following:
• Built-in ISOtechnology for True-Class-X SLC performance
• Dust-resistant photoelectric chamber
• Solid State, non-mechanical thermal sensor
• Microprocessor-based electronics with a low-profile plastic housing
All Model OH921 detectors are approved for operation within the UL- specified temperature range of 32°F to 100°F (0 –38°C).
Application Data
Installation of Model OH921 intelligent, addressable multi-criteria detectors requires a two-wire circuit.
In many retrofit cases, existing wiring may be used. `T-tapping’ is permitted only for Style 4 (Class B) wiring.
Model OH921 is polarity insensitive, which can greatly reduce installation and debugging times. When operating in NFPA
72 Class-X applications SLC polarity must be maintained to support up to 252 isolation ready devices per loop. When used
in mixed mode a maximum of 30 non-isolated devices between isolation devices (wired in polarity-insensitive mode). See
control panel install document for further details.
Model OH921 can be applied within the maximum 50-feet (15.24 m.) center spacing (2,500 sq. ft. [232.2 sq. m.]) per
Underwriters’ Laboratories. This application guide is based on ideal conditions, specifically, smooth-ceiling surfaces,
minimal air movement, and no physical obstructions between potential fire sources and the actual detector. Do not mount
detectors positioned near to heating | ventilation | air-conditioning (HVAC) outlets.
Exposed joists or beamed ceilings may also affect safe spacing limitations for detectors.
Should questions arise regarding detector placement, observe NFPA 72 guidelines. Good fire-protection system
engineering and common sense dictate how and when fire detectors are installed and used. Contact your local Siemens
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Fire Safety distributor or sales office whenever you need assistance applying Model OH921 in unusual applications.
Be sure to follow NFPA guidelines and UL Listed / ULC Listed installation instructions
– included with every Siemens – Fire
Safety detector
– and local codes for all fire-protection equipment.
Specifications
Model OH921 is a plug-in, (2) two-wire thermal (heat) detector, compatible with Cerberus PRO Modular | Model
FC9-series FACPs | FireFinder XLS/V. Each Model OH921 detector has microcomputer-chip technology and highly stable,
solid-state electronic circuitry. Model OH921 detectors utilize a modern, accurate and shock-resistant thermistor to sense
temperature changes. This electronic-sensing method virtually eliminates thermal lag associated with mechanical
temperature-sensing devices, and provides almost instantaneous temperature status to the FACP.
Model OH921 provides seven (7) field-selectable, pre-programmed temperature settings:
• Fixed 135°F (57°C) • Rate-of-Rise: 15°F / min. (8.3°C)
This feature is compatible with Cerberus PRO Modular systems, as well as with Cerberus PRO FC /FV922 or FC /FV924 and
FireFinder XLS/V FACPs.
Dimensional Data