Data Sheet for Product

Siemens
Smart Infrastructure - Building Products
–3–
usa.siemens.com/fire
Application Data
Installation of Model HI921 intelligent, addressable thermal detector requires a two-wire SLC circuit. In many retrofit
cases, existing wiring may be used. `T-tapping’ is permitted only for Style 4 (Class B) wiring. Model HI921 is polarity
insensitive when not used in Class-X mode, which can reduce installation and debugging times. The unit’s value is
multiplied with built-in ISOtechnology the True Class-X - NFPA 72 compliant SLC isolation feature supporting 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). Each detector fits into one (1) wall-or-ceiling footprint, and only occupies
one (1) address on the signal-line circuit (SLC).
Model HI921 can be applied within the maximum 50-feet (15.24 m.) center spacing (2,500 sq. ft. [232.3 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 in close proximity 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 – Fire Safety distributor or sales office whenever you need assistance applying Model HI921 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 HI921 is a plug-in, (2) two-wire thermal (heat) detector, compatible with Cerberus PRO Modular | FireFinder
XLS/V and Model FC9-series FACPs. Each Model HI921 detector has microcomputer-chip technology and highly stable,
solid-state electronic circuitry. Model HI921 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 HI921 provides seven (7) field-selectable, pre-programmed temperature settings:
Fixed Temperature set points (5)
Rate of Rise set points (2)
• Fixed 135°F (57°C)
• Fixed 145°F (63°C)
• Fixed 155°F (68°C)
• Fixed 165°F (74°C)
• Fixed 175°F (79°C)
• Rate-of-Rise: 15°F / min. (8.3°C) at fixed 135°F (57°C)
• Rate-of-Rise: 15°F / min. (8.3°C) at fixed 175°F (79°C)
Additionally, the Model HI921 detector has the following optional feature:
• Model HI921 provides indication of potential water freezing for sprinkler systems, via configuration for reporting a
low-temperature warning of 40°F (4.4°C).
This feature is compatible with Cerberus PRO Modular systems, as well as with FireFinder XLS/V and Cerberus PRO
FC/FV922 or FC/FV924 FACPs.
Mounting Diagrams | Dimensions
Model HI921