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Thermal Protectors

The outstanding quality level of our Thermal Protectors satisfies the highest demands for safety and reliability. They provide a patented, fully developed and reliable switching device system.
Benefits & Advantages:
    Compact & Pressure Stable
    • Ideal for installation in limited space, very suitable for mounting into and onto windings.
    Safe, Reliable & Durable
    • Constant contact pressure over the entire temperature range.
    • Over 70 tests conducted during the production process ensure reliability.
    • Approvals world-wide.
    • Very fast switching reduces arcing influence on the contacts.
    • Reproducible Switching Temperature provided by mechanical unstressed and electrically unloaded bimetal disc.
    • Factory-adjusted Nominal Switching Temperature (NST).
    • Excellent thermal coupling induced by a small-sized, low mass switching device
    • Wide range of operating supply voltage.
    • Extremely large assortment of lead-wires and solid wires available for connection.
Functions & Types:
  • Bimetal switch - After reaching its factory-adjusted Nominal Switching Temperature (NST) the bimetal disc suddenly snaps over from its stable initial position and thereby switches the contact.
  • Normally closed (NC) - Contact opens and switches off the supply => direct disconnection (01).
  • Normally open (NO) - Contact closes and activates the supply => i.e. switching on a fan or signal unit (02).
  • Resetting - After cooling down to below its factory-adjusted Resetting Switching Temperature (RST), the switching device suddenly snaps back into its initial position.
  • Max. Switching current Imax - Maximum current disturbed condition => i.e. during short circuit or on locked-rotor condit
Series PTC image

PTC Themistor Sensors

PTC (Positive Temperature Coefficient) Thermistor Sensors are temperature sensitive semi-conductive resistors, also known as Motor Protection Sensors or PTC resistors.

The reproducible change of resistance vs. temperature is utilized to activate trip relays, drive controllers, amplifiers, etc. When used to switch off load currents, activate alarms or initiate other controls, the result is defined temperature control of a variety of electrical equipment.

Thermik PTC Thermistor Sensors are supplied with an insulation cover (cap or sleeve) as standard.


Our PTC Thermistor Sensors satisfy the highest demands for safety and reliability.

  • Ideal for installation in limited space.
  • Suitable for mounting into or onto windings.
  • Multiple series connection of up to 6 sensors are available as standard.

  • Produced according to DIN 44081 (single) and DIN 44082 (triple) standards.

  • Excellent thermal sensitivity results from small size and low mass.

  • No drift or material fatigue.
  • The nominal response temperature remains constant for years.

  • Assortment of lead wires and lengths available for connection.


    Supply Voltage – DC Voltage (VDC)
    Ideally, PTC Thermistor Sensors should be operated with near zero current. The recommended supply voltage is 2.5 – 7.5 VDC, preferably pulsed. Thus, power consumption is minimized and self-heating is kept low. High current produces self-heating in the resistor and can cause tripping below the nominal response temperature.

    Multiple Sensor Connections
    The total resistance is the sum of all series connected single resistances. The resistance of a triplex configuration is 3x (≤250Ω) = ≤750 ohms (standard).

    Installation of PTC Thermistor Sensors
  • Place near the heat source (hot spot).
  • Mount or align in the same direction of the winding.
  • One sensor per phase in poly-phase motors.


    Click here to view Types
    Click here to view Temperature Resistance Diagram
    Click here to view Outline Drawings
    Click here to view Color Coding
    Click here to view How To Order