Thermal-LinksStructure and principle

Thermal-Links Structure and principle

Fusible Alloy type

Fusible alloy type thermal-links are available in two types, Axial type and Radial type.The operating principle and structure for the two types is basically the same.


Tin plated soft copper wire are welded to a fusible alloy with a lower melting point. For fusible alloy surely melting at the functioning on the surface, after coating the special rosin then insert in the insulation case. The structure is sealed completely by sealant on the case opening part.

Thermal-Links Structure and principle Fusible Alloy type Construction
Fusible alloy Special rosin Insulation case Sealant Lead wire

Operating principle

When thermal-links sense a abnormal heat cause by abnormal operation of component/equipment through thermal-links body and lead wire, the fusible alloy melt by reaching at the temperature of the melting point of the alloy.
An electrical circuit of the thermal-links is opened with forming two separate balls at the edges of the lead by surface tension of the melted fusible alloy.
Special resin accelerate the surface tension of the melted fusible alloy.

Pellet type

This thermal-links adopted metal casing and sense temperature material of organic compound pellet.


This is a completely seal off structure by sealant, and in the metalic case it has be installed with insulation bush and spring, movable contact, disc and thermal pellet.

Thermal-Links Structure and principle Pellet type Construction
Thermal pellet Metal case Disk Spring 1 Movable contact
Spring 2 Insulator bushing Sealant Lead wire1 Lead wire2

Operating principle

The current has flowed by the route of lead wire ⇔ movable contact ⇔ metallic case ⇔ lead wire before it functions.
The thermal pellet perceives heat when the ambient temperature rises, and it melts.
Spring expands when the thermal pellet melts, the movable contact pushes and separated from the lead, and the current is intercepted.

Thermal-Links/Resistor Assemblies Structure and principle

  • Thermal-links / Resistor assemblies is a kind of product that installed thermal cutoff and wire wound resistance element in one ceramic case then sealing with silicone cement.
  • Otherwise, it's also a kind of parts that resistor heat generated itself or sence abnormal heat generated from external by excess current and interception circuit.


Resistor Assemblies Structure and principle
Insulation case Sealant Resistor Thermal-Links Lead wire

Operating principle

  • Functioning mode1 Functioned by excess current
    Resistance element heatgenerated by excess current then transmitted to thermal-links to functioned and cut off the current.
  • Functioning mode2 Functioned by abnormal heat generated from external
    Ambient temperature of resistor is rising and the heat transmitted to thermal-links to cause functioned and cut off the current.