Thermotech Model 302 Heat Detector

This model is suitable for interior mounting in any atmosphere that is compatible with terminal screw type connections.

The Thermotech heat detector Model 302 is a normally open device designed especially for fire detection and alarm systems. These rate compensation type detectors are available in either 135°F. or 194°F. ratings. All four basic models are self restoring, hermetically sealed, shock and corrosion resistant, and are tamper-proof. Refer to NFPA STANDARD 72, STANDARD FOR AUTOMATIC FIRE DETECTORS for application requirements, testing and maintenance. the Thermotech heat detectors are not directionally affected, they can be mounted horizontally or vertically.

Principal of Operation
The Model 302 operates on the principles of a rate compensation detector. The detector consists of a high expansion aluminum tube which encases two insulation struts with opposing open contact points.

The high expansion sensing shell and the expansion struts have a different coefficient of expansion. A slow rate of temperature rise allows the heat to penetrate the inner expansion struts. Therefore, the tubular shell and the struts expand slowly until the total device has been heated to its rated temperature level of 135°F./194°F. At this point, the silver contact points close which initiates the alarm. When subjected to a rapid rate temperature rise there is not as much time for heat to penetrate the inner strut. The rapid lengthening of the shell allows the struts to come together at a lower level which compensates for thermal lag inherent in conventional fixed temperature detectors. When the surrounding air temperature goes below the rated temperature level, the shell contracts which forces contacts to open, thus automatically resetting the detector.

Special Considerations
Temp. Rating °F. Max Ceiling Temp. °F.
135 100
194 150

Detectors have a smooth ceiling UL rating of 50' x 50' (2500 sq. ft.). Detectors, hub covers, or outlet boxes must never be installed in direct sunlight. Refer to NFPA STANDARD 72for spacing and other considerations.

Electrical Rating
Voltage Current
6-125 VAC 5 amps
6-25 VDC 1 amp
125 VDC 0.5 amp

  • Underwriters' Laboratories
  • Factory Mutual
  • California State Fire Marshal. Listing No. 7270 0021:001
  • New York City Department of Buildings, MEA 193-03-E

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