Thermotech 302-ET-194


Heat Detector — Rate Compensation, All Weather, Vertical Mounting, FM & UL, 194 °F (90 °C)

Lead Time: 6-8 Business Days

  • Factory New
Brand: Thermotech Part #: 038854 Categories: , , , Manufacturer Part #: 302-ET-194 Tags: , ,


Model 302-ET, Hermetically sealed for moisture proof or dust proof installations. Requires no special back box. Has plastic hexagonal grip bushing with 1/2″ conduit threads for attachment to threaded hub cover, or any outlet box. Must be hand tightened only. For indoor and outdoor use. Protect from direct sunlight and adverse weather conditions.

General Information

Each model 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.

Principal of Operation

All models operate 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 constant 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 temperatures goes below the rated temperature level, the shell contracts which forces contacts to open, thus automatically resetting the detector. 

Special Considerations 

Temperature Rating °F. Max Ceiling Temperature °F.
135 115
194 155

Electrical Rating

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

Datasheet: 302-ET-194

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Weight 1.00 lbs
Thermal Rating


Detection Method


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