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Kidde Aerospace 12-100 – Thermal Switch / Detector
Part Number: 12-100 (also referenced as 12-100-XXX depending on set-point)
Manufacturer: Kidde Aerospace & Defense (Part of Collins Aerospace / RTX)
Common Synonyms: Spot Fire Detector, Thermal Switch, Fenwal-type Detector
Overview Section
The Kidde Aerospace 12-100 is a precision spot-type thermal switch designed for primary fire and overheat detection in high-value aerospace assets. This component is a critical "Safety of Flight" item, typically mounted in engine nacelles, auxiliary power unit (APU) enclosures, and wheel wells.
Utilizing the principle of differential expansion, the 12-100 operates as a normally-open switch that closes its electrical contacts when a specific temperature threshold (set-point) is reached. As a "resetting" detector, it will automatically return to the open (non-alarm) state once the temperature drops below the set-point, allowing for continuous monitoring after an overheat event has been addressed.
Enhanced Technical Data
| Technical Metric | Specification Data |
| Sensing Technology | Differential Expansion (Rate-Compensated) |
| Switch Configuration | Normally Open (SPST) |
| Voltage Range | 12 – 32 VDC (Standard Aircraft Power) |
| Current Rating | 2.0 Amps (Resistive) / 0.5 Amps (Inductive) |
| Set-Point Accuracy | $\pm 10°F$ to $\pm 25°F$ (Depending on Dash Number) |
| Operating Temp Range | $-65°F$ to $+1000°F$ ($-54°C$ to $+538°C$) |
| Weight | 0.12 lbs (approx.) |
| Material | Stainless Steel Shell (Hermetically Sealed) |
| Connector Type | Dual Stud or Screw Terminal (typical) |
Advanced Engineering & Structural Application
The 12-100 is engineered for Rate-Compensation. In fire detection, speed of response is critical, but false alarms must be avoided.
Engineering Insight: Differential Expansion
The switch consists of a stainless steel outer shell with a high coefficient of thermal expansion and an internal strut assembly with a lower coefficient. Under a slow overheat, both parts expand, and the switch triggers at its fixed set-point. However, during a rapid fire (high rate of rise), the outer shell expands more quickly than the internal struts, causing the switch to trigger earlier than its static set-point. This "anticipation" allows for faster extinguishing system activation during a flash-fire.
Hermetic Reliability
The internal contacts are hermetically sealed within the stainless steel housing to prevent contamination from engine oil, hydraulic fluid, or salt spray. This ensures the 12-100 remains operational in the most aggressive environments on the airframe.
Aircraft Compatibility
The 12-100 series and its derivatives are standard equipment on a vast array of legacy and modern platforms:
Boeing & Airbus: Used in secondary heat sensing roles and wheel well monitoring.
Lockheed C-130 Hercules: A staple for engine and APU overheat detection.
Bombardier CRJ/Challenger: Found in localized hot-gas leak detection points.
Bell & Sikorsky Helicopters: Critical for engine deck fire detection.
The Kidde Aerospace 12-100 represents the gold standard in mechanical fire detection. When every second counts, the rate-compensated design of the 12-100 ensures your fire suppression system is triggered at the earliest possible moment. Engineered to withstand the extreme vibrations and thermal loads of a jet engine nacelle, this hermetically sealed thermal switch provides the reliability required for Part 25 transport category aircraft. Trust genuine Kidde Technologies hardware to provide the precise overheat monitoring your airframe demands.
Installation & Maintenance Addendum
Mounting Torque: When installing the 12-100, do not over-torque the mounting flange or hex base. Deformation of the outer shell can change the internal clearances and shift the temperature set-point.
Continuity Testing: Use a high-impedance multimeter to verify the switch is open at room temperature. A "closed" reading at room temperature indicates a failed unit or one that has been exposed to a permanent over-temperature condition.
Lead Inspection: Check the terminal studs for signs of heat-related discoloration. If the leads show "blueing," the thermal switch should be replaced along with the associated wiring harness.
