The arcing contacts on low-voltage circuit breakers are often made of a silver and zinc alloy. Contact assemblies can have a butt or bayonet design, depending on the circuit breaker manufacturer’s requirements.Īn arcing contact is the contact of a switching device on which an arc is drawn after the main contacts have parted.Īrcing contacts are designed to prevent the main contacts from being damaged as the circuit breaker opens and closes. Air Circuit Breaker Ground DisconnectsĬontact assemblies for air circuit breakers include arcing contacts, main contacts, and auxiliary contacts. This ensures that the frame of the circuit breaker is grounded whenever there is the possibility of the frame being energized.įigure 4. The connection to the ground disconnect is the first connection made when racking a circuit breaker into the cubicle and is the last connection broken when racking it out of the cubicle. The ground disconnect connects the frame of the circuit breaker to the ground bus. The frame of a circuit breaker must be connected to the ground bus so that a short circuit or fault will be taken to the ground immediately and the protective devices will operate as quickly as possible. Air Circuit Breaker Secondary Disconnects For a low-voltage air circuit breaker, it is typical to connect and disconnect the secondary disconnects as the circuit breaker is racked in and out of its cubicle. Secondary disconnects are used to bring power into the circuit breaker for such features as the spring-charging motor, indicator lights, and control relays within the circuit breaker. However, ACBs can be bolted directly to the bus as a cost-cutting measure. It is typical for ACBs to have a draw-out construction in which the circuit breaker sits in a cradle that can be moved in and out of the enclosure or cubicle. The specific arrangement varies from OEM to OEM. On some circuit breakers that use current-limiting fuses, the load-side stabs have extenders installed to make the stab distances from the backboard uniform. If current-limiting fuses are installed on an ACB, the line-side stabs will sometimes be extended farther back from the circuit breaker backboard than the load-side stabs. Other types of air-frame circuit breakers with large continuous current ratings have a double row of primary disconnects rather than round disconnects. The round shape provides more surface area contact and can carry higher load currents than flat bus disconnects. Air circuit breakers with high frame ratings (3000 A to 4000 A) often have round (tulip-shaped) main disconnects. Air circuit breakers typically use either vertical or horizontal rows of spring-loaded fingers to make contact with the bus bar. Main disconnects connect a circuit breaker to the primary bus and allow load current to flow through the circuit breaker. Disconnects in a circuit breaker include main, secondary, and ground disconnects. Air Circuit Breaker Labeled Circuit DiagramĬircuit breaker disconnects (stabs) are current-carrying components that connect the circuit breaker to the bus or other connections. Air circuit breakers have six primary components, which include the following:įigure 1. Any part that is damaged or compromised can be repaired or replaced. Air Circuit Breaker (ACB) ConstructionĪir circuit breakers are completely renewable. In addition, the circuit breaker can be used as an across-the-line starter for large low-voltage motors. Air circuit breakers are typical of the draw-out design, although they can be bolted directly to the bus.Īir circuit breakers are used for applications in which there is a requirement for a more sturdy design than MCCBs and ICCBs offer. Low-voltage power circuit breakers (LVPCB) are often referred to as air circuit breakers (ACB).
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