Low-voltage circuit breakers are made for circuits rated at 600 V or lower. Though commonly perceived as not powerful enough, low-voltage circuit breakers are suitable for commercial circuit breaker usage.
Low-voltage circuit breakers are designed to automatically shut down once a unit becomes overheated. Afterward, the circuit breaker is reopened by spring action. This mixed-metal element, which is receptive to the heat produced by current flowing through it, has an inverse-time characteristic. If an extremely high current is developed, the circuit breaker will be tripped very rapidly.
When the two separable contacts of an air circuit breaker are opened, an arc develops between them. Different manufacturers use different designs and arrangements of contacts and their surrounding chambers. The most well-known design places the moving contacts inside an arc chute. The design allows the arc formed as the contacts open to draw out into the arc chute. When the arc is drawn into the arc chute, it is divided into small segments and quenched. This action extinguishes the arc rapidly, which minimizes the chance of a fire as well as damage to the breaker contacts.
Generally, much larger air circuit breakers are used for commercial and industrial distribution systems. To delay the expensive process of upgrading circuit breaker systems, some corporations use low-voltage circuit breakers in conjunction with larger breakers. Larger circuit breakers have current ratings as high as 4000 A and interrupting ratings as high as 150,000 A.