The 140U-JD3D3-D10 circuit breaker from Allen-Bradley is a circuit breaker from the 140U product line. A circuit breaker is a device designed for use in electrical systems. It is used to open/close a circuit by manual means and to open a circuit automatically when a preconfigured overcurrent threshold is reached while the breaker is being used within its current rating. Another way to define a circuit is as a mechanical switching device that is capable of breaking, making, and carrying currents under normal circuit conditions and breaking current circuits under abnormal or short circuit conditions. The specifications for the 140U-JD3D3-D10 circuit breaker include 3 poles,100 Amps of current rating, a JD-type of breaker frame, and 30 to 39 kiloamps of interrupting rating. A thermal-magnetic trip module is incorporated into the breaker. The magnetic settings on the trip module are user-adjustable.

The Bulletin 140U product line supports two types of trip modules: electronic and thermal-magnetic. Breakers with electronic trip modules are available for current ratings ranging from 70 to 1200 Amps while breakers with thermal-magnetic trip modules are available for ratings ranging from 15 to 800 Amps. Molded case circuit breakers (also known as feeder breakers) such as the 140U-JD3D3-D10 circuit breaker are designed to provide overcurrent protection for equipment/conductors by opening automatically before the circuit current reaches a threshold value and duration that will give rise to dangerous or excessive temperatures in the conductor insulation or the conductor itself. Originally circuit breakers were available with only thermal-magnetic trip modules. Electronic trip modules offer an advanced degree of customization by allowing protection curves to be tailored to user requirements. Only trained technicians should be involved in the installation and maintenance of the 140U-JD3D3-D10 circuit breaker.