Simple electromechanical thermostat teardown

STEGO KTO 011 is electromechanical thermostat designed for controlling electrical heating. The thermostat has one NC (normally closed) contact that normally conducts, but opens when temperature exceed the set temperature.


The temperature control range is 32-140F. The electrical NC contact is rated for AC120V 16(2)A and AC250V 10(2)A. Let’s open the device.



The temperature controlling us done with this contruction that consista of bimetallic strip, electrical switch mechanism and temperature control knob.



The switch mechanism seems to use same type of quick activication spring mechanism that some microswitches use. It provides sharp quick operation and some hysteresis. The mechanism has marking TKP-1 16A 250V AC 0-60 NC.



  1. Tomi Engdahl says:

    European Ratings

    The typical European rating will distinguish between resistive and inductive load ratings. Below is an example of a typical European rating:
    16(4)A 250V ~ T85 µ

    In this example the 16 = resistive load amperage; (4) = inductive load amperage; A= amperage; 250V= voltage; ~ = AC; T85= Maximum operating temperature in centigrade; µ = micro-gap (<3mm) approved.

    If there is less than 3mm of air space between a switch's contacts in the open position, a micro-gap approval (µ) may be granted. This mark indicates that the switch has general application approval with a qualifier that another device, such as a cord and plug, must provide an alternate means of disconnection from the main power source.

  2. Tomi Engdahl says:

    The mechanical thermostats KTO 011 and KTS 011 are two state regulators used to control heaters, coolers, filter fans or signal devices.

    KTO 011: Thermostat (normally closed); contact breaker for regulating heaters. The contact opens when temperature is rising.

  3. Tomi Engdahl says:

    Contacts are rated also for DC:
    DC 24-72 V

  4. Ramesh says:

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