To extend the service life of the product, materials used for electrical contacts must possess the following good properties.

1. Good electrical and thermal conductivity

2. Good anti-welding performance;

3. High resistance to electrical wear;

4. Good mechanical properties and weldability;

5. Chemical stability;

6. Low gas content.

Commonly Used Contact Materials in Circuit Breakers:

1. Silver Cadmium Oxide (AgCdO)
Cadmium oxide content: 5%–15%. AgCdO12 and AgCdO13 are most commonly used.
AgCdO has anti-welding performance second only to silver graphite. It offers high conductivity, low and stable contact resistance, and the best corrosion resistance among silver-based materials with over 85% silver content.

2. Silver Tin Oxide (AgSnO₂ + In₂O₃)
Higher thermal stability than AgCdO, with other properties comparable to AgCdO.

3. Silver Zinc Oxide (AgZnO)
Zinc oxide content: 8%–10%. Good anti-welding and arc erosion resistance. Mainly used in small to medium capacity circuit breakers (typically ≤63A).

4. Silver Copper Oxide (AgCuO)
Copper oxide content up to 10%. Excellent anti-welding and electrical wear resistance. Mainly used in medium-capacity circuit breakers.

5. Silver Nickel (AgNi)
Nickel content: 10%–40%. Higher nickel content reduces conductivity but increases hardness and mechanical wear resistance. AgNi has better anti-welding performance than silver and hard silver alloys at small to medium currents, but inferior to AgCdO. Under high currents, AgNi welds easily and must be paired with silver graphite.
Alloys with <20% Ni are used for 10A auxiliary contacts; those with >30% Ni are used for breakers up to several hundred amperes.

6. Silver Graphite (AgC)
Graphite content: typically 3%–5%. Completely non-welding, but must be paired with other contact materials. Pairing AgC with AgNi30 or AgNi40 achieves good results in circuit breakers.

7.Silver Tungsten (AgW)
Tungsten content: 20%–80%, with a small amount of nickel. Hardness and resistivity increase with tungsten content. AgW has high resistance to high-current arcs; alloys with 70%–80% tungsten have the highest arc erosion resistance among all contact materials. Anti-welding performance is similar to AgNi, and can be improved by pairing with AgC.
AgW has low conductivity and easily forms surface films of tungsten oxide and silver tungsten, leading to increased contact resistance, temperature rise, and potential welding under short circuits.
Selection and pairing of contact materials are key technical aspects in the design and manufacturing of circuit breakers. Different materials have their own advantages and disadvantages in terms of electrical conductivity, anti-welding performance, arc erosion resistance, and thermal stability. In practical applications, scientific matching should be carried out based on current rating, breaking capacity, and operating environment. As environmental regulations become increasingly stringent and the demand for reliability of electrical equipment continues to rise, new environmentally friendly contact materials represented by silver tin oxide (AgSnO₂) and silver tungsten carbide (AgWC) are gradually becoming hotspots in research and application. Proper material selection and optimized pairing can not only significantly extend the service life of products but also serve as an important cornerstone for ensuring the safe and stable operation of power systems.