Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

air circuit breaker
a power circuit breaker where the power contacts operate in air. Some versions employ an air blast to extend and clear the arc on contact opening, while others employ arc chutes with magnetic or thermal assists.
air-blast circuit breaker
a circuit breaker in which the arc which forms between the contacts on opening is extinguished with a blast of high-pressure air.
circuit breaker
a circuit breaker is a device that makes and breaks the electrical contact between its input and output terminals. The circuit breaker is capable of clearing fault currents (tripping) as well as load currents. The circuit breaker consists of power contacts with arc clearing capability and associated control and auxiliary circuits for closing and tripping the breaker under the required conditions.
gas circuit breaker
a circuit breaker in which the arc between the contacts is extinguished by immersion in or a blast of an electronegative gas.
instantaneous-trip circuit breaker
essentially an inverse-time circuit breaker with the thermal element removed. It will only trip magnetically in response to short-circuit currents. Thus, it is often referred to by other names, such as magnetic circuit breaker and magnetic-only circuit breaker.
inverse-time circuit breaker
a circuit breaker in which the allowed current and time are inversely proportional. It contains a thermal element and a magnetic element in series. The thermal element is designed to trip as a result of heating over time in response to overload currents, while the magnetic element is designed to trip magnetically, with no intentional time delay, in response to short-circuit currents. Also called a thermal-magnetic circuit breaker.
molded case circuit breaker
a low voltage air circuit breaker that includes thermal and/or magnetic overcurrent sensing which directly trips the breaker. The molded case circuit breaker is nearly always manually closed, opened, and reset.
oil circuit breaker
a power circuit breaker that uses oil as an insulating and arc-clearing medium.
residual current circuit breaker
European term for ground fault interrupter.
SF6 circuit breaker
a power circuit breaker where sulfur hexaflouride (SF6)gas is used as an insulating and arc clearing agent.
vacuum circuit breaker
a power circuit breaker where a vacuum chamber is used as an insulating and arc clearing medium.