Understanding Circuit Breaker Contacts

A circuit breaker is a safety device used to protect an electrical circuit from damage caused by excess current from an overload or short circuit. Its basic function is to interrupt current flow when a fault is detected. Key components include contacts that open and close the circuit.

Circuit breakers typically have two main types of contacts:

• Main contacts: These contacts carry the normal load current when the circuit breaker is closed. They are designed for low resistance to minimize power loss and heat generation during normal operation.
• Arcing contacts: These contacts are specifically designed to handle the electric arc that forms when the circuit breaker opens under load or fault conditions. They are the last to open and the first to close, taking the brunt of the arc energy.

Circuit Breaker Material: Copper Tungsten Alloy

The choice of material for these contacts is critical. Main contacts are often made of materials with high electrical conductivity and low resistance, such as pure copper or silver-plated copper.

However, arcing contacts face extreme conditions. When the circuit opens under load, the current flow doesn't stop instantly. Instead, an electric arc forms between the separating contacts. This arc is intensely hot and can cause significant damage, erosion, and welding of the contact surfaces if the material isn't robust enough.

Why Copper Tungsten is Used for Arcing Contacts

Copper tungsten (CuW) alloy is a composite material known for its excellent combination of properties that make it ideal for applications involving electrical arcing:

• High Melting Point: Tungsten has a very high melting point ($> 3400 \text{°C}$), which helps the alloy withstand the extreme temperatures of the electric arc.
• Arc Resistance: The material resists erosion and burning caused by the arc, ensuring the contacts can perform reliably over many operations.
• Good Electrical Conductivity: Copper provides high electrical conductivity, allowing the contacts to carry current efficiently before and after arc interruption.
• High Density and Hardness: These properties contribute to the material's resistance to mechanical wear during the opening and closing operations.

Because the arcing contacts are subjected to the intense heat and wear of the electric arc, they are typically made from materials like copper tungsten alloy or silver tungsten alloy. These materials can withstand the harsh environment created by the arc, protecting the main contacts from damage and ensuring the circuit breaker's ability to interrupt fault currents repeatedly.

Therefore, the part of the circuit breaker specifically designed to withstand the electric arc and often made of copper tungsten alloy is the arcing contact.