The 140G-J2X3 circuit breaker is a molded case circuit breaker frame from Allen-Bradley/Rockwell Automation. It belongs to the Allen-Bradley 140G series of circuit breakers. The 140G-J2X3 circuit breaker, like other molded case circuit breakers in the same family, is used in an industrial setting to provide overcurrent protection. Note that this overcurrent protection encompasses short circuit protection and thermal overcurrent protection. Also, note that the short circuit range depends on the power source and where the short circuit would occur in the circuit. The Allen-Bradley 140G-J2X3 circuit breaker, like other molded case circuit breakers, features an arc chamber which surrounds the switching contacts. During a short circuit, the contacts open, generating an arc. The arc chutes and splitter plates found in the arc chamber draw the arc away from the contacts, dividing and cooling the arc. Consequently, the arc is extinguished and the flow of current is stopped. 

The 140G-J2X3 circuit breaker supports a fixed thermal and fixed magnetic trip unit. The thermal part of the circuit breaker uses a bimetallic strip. As with a traditional overload relay, there is a deflection on the bimetal element when the bimetal is heated. This exerts pressure on a trip bar, causing the breaker to trip. However, the magnetic aspect of the trip unit found on the 140G-J2X3 circuit breaker uses magnetic forces created by a current flowing in the opposite direction. This effect assists in the opening of the contacts under high circuit conditions. Note that the magnetic force generated is proportional to the value of the short circuit current sensed by the breaker.