ZH437 Series

Overtemperature protection device, medium

Overtemperature protection device

Schaltbau fusible overtemperature protection and tripping devices ensure fail-safe thermal cutout protection against overheating of electric air heaters as used in rail vehicles and stationary heating systems. The devices are a prerequisite for fire protection and operate totally independent of the heater controls.

The device must be wired into the heater load circuit. Prior to installation, every device of the various series must be fitted with a fusible link. Fusible links are available with a number of trip temperatures, so you can order the one fusible link which meets exactly the requirements of your application. That is why fusible links are not included in delivery of any overtemperature protection or tripping device.

Insufficient air flow or failure of heater control results in rapid overheating of the system. When the fixed temperature set point of the fusible link is exceeded, the device shorts the heater load circuit, tripping a series-connected fuse. This stopps the flow of current through the components, and provides protection against any return to operation of the heaters in an overtemperature condition.


  • Reliable overtemperature protection of high-voltage heating registers
  • Tripping function independent of control voltage and electronic regulation
  • Fusible links available for various trip temperatures
  • Standards: IEC 60077, EN 50124-1

Ordering code


Dimension diagram

  • Fusible links are available with various trip temperatures and, therefore, not included in delivery but to be ordered individually. See also table with other fusible links.

By selecting this option you finish the configuration.



Nominal voltage Un1,800 V
Type of voltageDC, AC
Rated insulation voltage Ui4,000 V
Ingress protection rating, IEC 60529IP54
Optional componentsStandard
Thread size of fusible linkM3
Auxiliary contacts---
Series-connected fuse≤ 100 A
Max. ambient temperature of insulator200 °C
Mechanical endurance5 tripping operations min.
Weightapprox. 650 g
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ZH437 – Overtemperature protection device, medium