How Circuit Breaker Arc Chutes Work
The arc chutes for molded case circuit breakers and old power breakers look simple enough, but they actually are a complex design and perform extremely important functions. For excitement, read the patent application for an old circuit breaker arc chute, if you can stay awake. MIDWEST sometimes is asked to explain what an arc chute does. We always go for the short version. Basically an old or new circuit breaker arc chute stretches the arcing that takes place when a circuit breaker opens, such that the arc is too long for the voltage to keep it going. Arc chutes have arc dividers in the form of flat segments stacked one above the other, with an air gap between them. When the arc occurs, it is expelled into the arc chute and into the arc dividers, such that it wraps back and further between the arc dividers. The wrapping back and forth around the arc dividers effectively stretches the length of the arc until it is just too long for the voltage to keep it going. When this happens, the arcing stops. The arc has been extinguished. When the circuit breaker opens, the main current carrying contacts open first and a different set of contacts, the arcing contacts, open second, such that the arcing contacts endure limited damage from the arcing, until the arc chutes interrupt the arc. So the combination of the arc chutes and the arcing contacts protect the main contacts from arcing damage when the circuit breaker opens and when it closes. When a circuit breaker is closed, the arcing contacts close first, again taking on the arc such that the main contacts are protected from arcing damage when closed. This is especially important when the circuit breaker interrupts a high current fault and there is a real blast in the arc chutes. Each phase, ie pole, of a circuit breaker has a separate arc chute. This is pretty much how the arc chutes of obsolete, old, and new replacement circuit breakers operate. So the arc chutes perform an extremely important function.