SEKI ST-22 Bimetal Thermal Switch

SEKI’s ST-22 thermal cut-out is a reliable thermal protection devices for overheat and over-current protection in electrical circuits.  Its small size belies it’s ability to switch 7A/250VAC loads in electric motors, solenoids and transformers.

The neat plastic case houses a snap-action bimetal blade that is pre-calibrated to a precise operating temperature.  As the temperature rises, this blade snaps from a concave shape to convex and opens a set of electrical contacts, thus breaking the circuit.  On cooling the blade returns to its original shape and re-makes the circuit.

The SEKI ST-22 has 70mm XLPE leads as standard but other lengths are available for volume enquiries.  The housing is IP45 rated and epoxy sealed to ensure long-term reliability and integrity.  Calibrations from 50℃ up to 150℃ (in 5K steps) are readily available with a thermal differential (reset temperature) of around 30% of the value of opening set-point.


  • Electric Motors
  • Transformers
  • Heating Pads
  • Solenoids
  • LED Lighting
  • Battery Chargers
  • Power Supplies


  • Snap Action with Automatic Reset
  • Contact Rating: 7A/250V AC (10,000 cycles)
  • Temperature Setting Range: 50℃ to 150℃
  • UL/cUL, VDE, CQC, KC
  • PBT Resin Case – Epoxy Sealed
Seki ST-22 Bimetal thermal cut-out - Overheat thermal protector ST-22 Drawing 1