The Allen-Bradley 140U-LTD3-D30 Trip Unit comes with the thermal/magnetic protection type and with 300 Amps of rated current. It is compatible with the 600 Amps, Frame L MCCBs. The adjustable current range of the magnetic trip is 1500 to 3000 Amps. This trip unit provides thermal overload, short circuit, and ground fault protection. It is an electromechanical trip unit that has moving parts inside it. The trip unit ensures machine protection by opening the contacts automatically. It can be manually tripped by pressing a button. The 140U-LTD3-D30 Trip Unit is designed to sense the heat caused by an overload condition to provide protection for industrial power distribution circuits. It employs a bimetallic strip to sense overload conditions. When a short current occurs, it will create a magnetic force that will unlatch the trip unit. This trip unit is an interchangeable trip unit which is called a rating plug. Its instantaneous magnetic tripping characteristics cause instantaneous trips when the current reaches a set point.

The Allen-Bradley 140U-LTD3-D30 Trip Unit is suitable to provide protection for DC networks and electrical distribution systems. The 140U-LTD3-D30 Trip Unit opens a circuit automatically in a pre-defined overcurrent situation that can cause damages to the breaker. The breakers with this trip unit can be used in large electrical circuits with generators, motor control circuits, commercial electrical systems, and heavy-duty applications. If the ambient temperature is above 40 degrees Celsius, the unit will carry less current compared to its continuous current rating while making nuisance tripping. During installation, the circuit breaker handle must be in the "tripped" position or "off" position so that the technicians can remove the cover.