Siemens OP921 (S54320-F4-A2) — plug-in, two-wire addressable photoelectric smoke detector for Cerberus PRO and FireFinder XLS systems, using a light-scattering optical sensor with microcontroller-based signal processing.
The OP921 consists of a dust-resistant photoelectric chamber and microprocessor-based electronics in a low-profile plastic housing, and ships with a protective dust cover. Advanced software algorithms analyse the optical signal for stable, accurate smoke detection with automatic environmental compensation and strong EMI/RFI immunity. Rather than a single fixed sensitivity, the panel selects one of four pre-programmed application parameter sets — Sensitive, Standard, Robust or Air-duct — to match the environment. The detector is UL Listed as a self-testing device and performs complete diagnostics every ten seconds, so no field sensitivity test is required. A tri-color status LED gives 360-degree indication, and SureWire technology makes the device polarity insensitive.
Specifications
| Part number |
S54320-F4-A2 |
| Detector type |
Plug-in, two-wire addressable photoelectric (light-scattering optical) smoke detector |
| Operating temperature |
+32°F to +120°F (0°C to +49°C) |
| Relative humidity |
0 to 95%, non-condensing |
| Air pressure |
No effect |
| Air velocity |
0 to 4,000 feet per minute (0 to 20 m/s) |
| Input voltage range |
16 VDC to 30 VDC |
| Alarm current, max. |
280 µA |
| Standby current, max. |
280 µA average |
| Maximum spacing |
30-ft. centers (900 sq. ft.), per NFPA 72 |
| Detector weight |
0.317 lbs. (0.144 kg) |
| Application parameter sets |
Four: Sensitive, Standard (default), Robust, Air-duct |
| Self-diagnostics |
Complete diagnostics every 10 seconds; sensitivity self-monitored within UL Listed limits |
| Status indication |
Tri-color LED with 360-degree view |
| Compatible panels |
Cerberus PRO FC901, FC922, FC924, FV922, FV924, Cerberus PRO Modular; FireFinder XLS and XLSV |
| Mounting base |
DB-11 (500-094151) or DB-11E (500-094151E); ordered separately |
| Mechanical protection guard |
UL and ULC Listed with STI Guard Model STI-9604 |
| Listings and approvals |
UL 268A Listed for direct air-duct use, ULC Listed; FM (#3230, #3210) and CSFM (#7272-0067:0258) Approved; RoHS compliant |
Installation notes
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Base ordered separately: the head plugs into a DB-11 or the smaller DB-11E. In Canada order the DB-11C (500-095687).
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Pick the parameter set deliberately: Standard is the default and suits office and hotel-lobby spaces; Robust is the one to select where cigarette smoke or exhaust fumes cause nuisance alarms; Sensitive suits clean, controlled areas where early detection of open fires is the priority.
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Direct in-duct without a housing: the Air-duct parameter set is what makes the detector UL 268A (DI) compliant for direct in-air-duct use with no duct housing. Selecting it is not optional in that application.
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No field sensitivity test: the detector is UL Listed as self-testing and monitors its own sensitivity, and it reports sensitivity remotely at the panel.
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Mixed loops: compatible with Siemens H-series devices on the same loop when used with Cerberus PRO Modular, FireFinder XLS/V, or FC/FV 9-series panels.
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Guarding: only the STI-9604 guard is UL and ULC Listed with this detector; a generic cage is not a listed assembly.
Related models
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FDO421 (S54320-F4-A1) — the same detector with the same published technical data, catalogued for the Desigo Fire Safety platform instead of Cerberus PRO
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OOH941 (S54320-F7-A2) — multi-criteria dual-optical and thermal head where a single optical sensor is not enough
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OOHC941 (S54320-F8-A2) — multi-criteria fire and CO detector, adding a carbon monoxide sensor
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HI921 (S54320-F5-A2) — heat detector for the same platform and base, where smoke sensing is unsuitable
Specifications taken from the Siemens data sheet "Cerberus® PRO Photoelectric Smoke Detector, Model OP921," document 9902 (October 2017, Rev. 6). Manufacturer specifications are subject to change without notice.
