Bimetallic switch

Bimetallic switches are used in the electrical industry for automatic temperature monitoring. Unlike the PTC thermistors, they require no trigger device and thus limit the temperature of devices or parts that are to revert automatically after cooling. Bimetallic switches are available in three different constructions: types C0x, S0x and L0x.

Technical information on bimetallic switches

At a glance

•    Switching points +60°C ... +200°C
•    Switching tolerances: ΔT = ±5 K ... ±2,5 K
•    Switching currents up to 25 A
•    Opener or closer versions
•    Single, twin or triplet design
•    Compact construction
•    Short reaction time
•    For flexible use
•    Numerous variants
•    Broad temperature spectrum


  • Electric motors, transformers, generators
  • Cooling elements
  • Carbon brush holders
  • Transformer plates
  • Hotplates
  • Plate and cup warmers
  • Coffee machines, preserving machines, waffle makers
  • Shrink film devices, film sealing devices
  • Sealing equipment
  • Warm water storage systems
  • Heating boilers, heating systems
  • Industrial fan heaters
  • Analysis devices
  • Steam showers
  • And much more


  • Drive technology
  • Mechanical and plant engineering
  • Energy generation
  • Sanitation, heating and air-conditioning
  • Building services
  • Other

Technical information on bimetallic switches


If the nominal activation temperature is exceeded in case of overheating, the (load) circuit is opened – or closed –, for example to add a fan, trigger an alarm or completely interrupt the power supply. Heat transmission usually occurs from all sides through convection, radiation or conduction in gaseous or solid media.

Types in series C01/02 and C06/08 are current insensitive, have an uninsulated metal housing and are conductive. They are used in areas in which there is already sufficient insulation or when no housing insulation in necessary.

Types in series S01/02 and S06/08 are current insensitive and insulated. Insulation comes from assembly with Kynar shrinking tube, Mylar (≤ 130°C) or Nomex cap (≥ 135°C). This gives the switches high voltage resistance up to 2 kV at AC 50 Hz and 1min, and protection class I VDE. They are ideally suited to installation in windings of motors, transformers and coils.

Types in series L0x are non-current-sensitive temperature monitors in aluminium screw-in housing, sealed in epoxy resin on the connection side. They are screwed into cooling units, carbon brush holders, transformer plates etc. This gives the switches high voltage resistance up to 2 kV at AC 50 Hz and 1 min, and protection class I VDE. Available as opener and closer.


Bimetallic switches are used for control purposes and for temperature-dependent automatic switching processes. They are found in many household and heating appliances, for example to control the temperature of irons, coffee machines and kettles, as well as in circuit breakers, fire alarms and for valve control. In addition, temperature limiters are mainly used in mechanical engineering, drive technology and special applications for the automotive sector. Thanks to their high pressure resistance, bimetallic switches are also ideal for installing on or in the winding of electric motors.

Operating principle

Bimetallic switches consist of two different metals, firmly bonded or interconnected together (bimetallic disc). The different material properties mean that the bimetallic disc can expand or contract. When a prescribed maximum temperature is reached, the bimetallic disc suddenly flips due to expansion, opening or closing a contact. The bimetallic disc then only returns to its original shape automatically after significant cooling.

The available bimetallic switches provide the following advantages, depending on the version:

  • Switching points +60°C ... +200°C
  • Switching tolerances: ΔT = ±5 K ... ±2.5 K
  • Switching currents up to 25 A
  • Low contact resistance
  • High sensitivity
  • Current-sensitive and non-current-sensitive versions
  • Vibration-proof up to 100 m/s² (10–60 Hz)
  • All built-in switches also available in twin or triplet circuits
  • Suitable for (vacuum) impregnation processes in winding heads
  • Outstanding long-term stability
  • VDE, UL, CSA approved versions possible

The built-in switches are available in two different maximum switching capacities at 6.3 A (type 01/02) or 25 A (type 06/08), as openers (type 01/06) or closers (type 02/08), as single, twin or triplet sensors. The feed to the switches consists of radiation-cured plastic and is stripped 5 mm at the ends. Depending on the maximum switching current, it is supplied in 0.25 mm² or 0.75 mm². Needless to say, in addition to the standard cable length of 300 mm, we can also provide any cable length and deliver Teflon materials as insulation material.