Understanding the Silver Contact Point

The so-called silver point of a circuit breaker refers to the small area of silver-based electrical contact material bonded to the working surface of the contact. It is mechanically fixed to the copper arm or contact carrier through riveting, brazing, or multilayer composite bonding.

It is not pure silver.
It is a carefully engineered composite.

Despite the high market price of silver, these contacts hold little scrap value because performance, not material purity, defines their purpose.

The silver contact fulfills three fundamental roles:

• Current carrying: low contact resistance, minimal temperature rise, and long-term electrical stability.

• Current interruption: resistance to arc erosion, maintaining surface integrity under repeated breaking operations.

• Anti-welding: preventing fusion during short-circuit conditions or intense arcing events.

To achieve this balance, the industry universally adopts a silver matrix combined with a second phase. Silver contributes conductivity and thermal diffusion, while the second phase enhances arc resistance, anti-welding capability, wear resistance, and surface stability.

The most common systems include AgNi, AgSnO₂, AgW, AgWC, and AgC.

1. Single-Phase Constituents

1.1 Ag (Silver)

Silver forms the backbone of all contact systems.

Advantages
Exceptional electrical and thermal conductivity enable low contact resistance and efficient heat dissipation. Localized hot spots are quickly diffused.

Limitations
Silver is relatively soft and has a modest melting point. Under high arc energy, it melts easily, splashes, and erodes, increasing the risk of material loss and contact welding.

Conclusion
Silver alone is insufficient. A reinforcing second phase is mandatory.

1.2 Ni (Nickel)

Typical content: ~5–30%

Nickel increases hardness, wear resistance, and resistance to material transfer. Anti-welding performance improves noticeably.

The trade-off is unavoidable. Electrical and thermal conductivity decline as nickel content rises. Higher nickel ratios also increase forming difficulty and bonding stress during manufacturing.

1.3 SnO₂ (Tin Oxide)

Typical content: ~8–15%

Tin oxide enhances arc erosion resistance and anti-welding behavior. As its proportion increases, contact durability improves, but conductivity decreases. Contact resistance and service life become highly dependent on powder dispersion and process control.

Small additions of modifying oxides, such as In₂O₃, are often used to stabilize performance and batch consistency.

1.4 W (Tungsten)

Typical content: ~20–90%

Tungsten delivers exceptional resistance to arc erosion, welding, and crater formation. It is the material of choice for high-energy interruption.

However, it significantly reduces conductivity, complicates processing, and raises cost. Machining and bonding demand precision.

1.5 WC (Tungsten Carbide)

Typical content: ~20–65%

WC offers extreme hardness, wear resistance, and shape retention. Contacts retain their geometry even under aggressive mechanical wear.

The downside is brittleness. Processing tolerance is narrow, and conductivity suffers. Structural design must compensate for its rigidity.

1.6 C (Graphite / Carbon)

Typical content: ~3–5%

Carbon suppresses adhesion and material transfer, reducing welding tendency. It behaves like a release agent under arc stress.

Yet contact resistance rises, thermal performance weakens, and sensitivity to contact pressure increases. Carbon content is therefore kept deliberately low.

2. Silver Contact Systems

2.1 AgNi (Silver-Nickel)

Positioning
A general-purpose, stable solution with consistent contact resistance and good wear behavior. Manufacturing repeatability is excellent.

Composition balance

• Low Ni (5–15%): better temperature rise control and overall stability.

• High Ni (20–30%): improved wear resistance and anti-welding, but increased thermal sensitivity.

2.2 AgSnO₂ (Silver–Tin Oxide)

Positioning
A well-balanced system for arc resistance and anti-welding, widely adopted in modern breakers.

Composition balance

• High SnO₂: superior arc endurance and welding resistance, but reduced conductivity and stricter process demands.

• Low SnO₂: improved thermal performance and contact stability, with limited arc endurance margin.

Modified oxides are commonly added to enhance reliability.

2.3 AgW (Silver–Tungsten)

Positioning
Designed for strong arcs and high-energy interruption scenarios.

Composition balance

• High W: outstanding arc resistance and surface stability, but higher temperature rise, cost, and processing complexity.

• Moderate W: a compromise between electrical performance and arc endurance.

2.4 AgWC (Silver–Tungsten Carbide)

Positioning
Combines high arc resistance with extreme wear resistance.

Composition balance

• High WC: excellent shape retention and wear resistance, but increased brittleness and stringent process requirements. Structural design must accommodate its rigidity.

2.5 AgC (Silver–Carbon)

Positioning
Optimized for anti-adhesion and suppression of material transfer.

Composition balance

• Higher C: reduced welding tendency, but sharply increased contact resistance and temperature rise. Carbon content remains minimal due to pronounced side effects.

3. Conclusion

As the proportion of the second phase increases, arc resistance, anti-welding performance, and wear resistance improve.

At the same time, electrical conductivity, thermal diffusion, and temperature rise margins deteriorate.

Silver contact engineering is therefore not about selecting the “best” material.
It is about choosing the most appropriate compromise—aligned precisely with current level, interruption energy, mechanical duty, and thermal constraints of the circuit breaker.