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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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The arcing contacts of circuit breaker are made of
Stainless steel
Carbon
Porcelain
Copper tungsten alloy
Copper tungsten alloy
Quick Summary: Arcing contacts in a circuit breaker are made of copper-tungsten alloy because it combines the high electrical conductivity of copper with the extremely high melting point and arc resistance of tungsten. This material composition prevents the contacts from melting or fusing during the intense heat generated when the circuit is interrupted under load.
Arcing contacts in a circuit breaker are made of copper-tungsten alloy because it combines the high electrical conductivity of copper with the extremely high melting point and arc resistance of tungsten. This material composition prevents the contacts from melting or fusing during the intense heat generated when the circuit is interrupted under load.
H∝I2Rt — Heat generated by arc at contact interface
R=ρAl — Contact resistance determining steady-state losses
When a circuit breaker opens, an electric arc is formed between the contacts due to ionization. The energy released by the arc is proportional to I2Rt. Since tungsten has a very high melting point (3422°C), it resists erosion by this heat, while the copper matrix ensures low contact resistance, reducing I2R heating losses during normal operation.
Tungsten acts as a heat sink, preventing welding of contacts.
Copper ensures minimal voltage drop across the closed contact.
Copper-tungsten is produced via powder metallurgy.
Prevents contact sticking (seizing) during heavy fault current interruption.
Excellent resistance to electrical erosion
High mechanical strength at elevated temperatures
Superior thermal conductivity
More expensive than pure copper or brass
Difficult to machine due to hardness
SF6 Circuit Breakers
Vacuum Circuit Breakers
Oil Circuit Breakers
Stainless steel is used for mechanical enclosures, not arcing contacts.
Carbon is used in brushes for rotating machines, not for high-energy arc interruption.
Porcelain is an insulating material, not a conductor.
D is correct — The copper-tungsten alloy provides the ideal balance of thermal management and arc-erosion resistance necessary for high-power switching.
Always remember that in switchgear, conductivity is needed for current flow, but thermal stability is the primary requirement for the material that bears the brunt of the arc.