The Allen-Bradley 140U-LTD3-D40 Trip Unit comes with the thermal/magnetic protection type and 400 Amps of rated current. It is compatible with 600 Amps rated Frame L 3-pole molded case circuit breakers (MCCBs). The adjustable current range of the magnetic trip is 2000 to 4000 Amps. This trip unit can be used to provide short circuit protection, ground fault protection, and thermal overload protection. This is an electromagnetic switch that has current and thermal sensitivity. This trip unit is designed to sense the high current that is caused by a short circuit so it can stop it to protect the equipment in large electrical circuits. The 140U-LTD3-D40 Trip Unit also has a manual trip button that can trip the breaker manually.

The 140U-LTD3-D40 Trip Unit is the part of the MCCB which determines when to open the contacts. To activate the trip mechanism, the bimetallic strip bends to a predetermined distance and it makes a contact with the trip bar. The actions of the magnetic field that is generated inside the trip unit force the contacts apart in a faulty current. It also has adjustable magnetic elements to provide short circuit protection. The thermal-magnetic trip provides protection against long term current overloads that last longer than 10 seconds. It can be used to provide protection to networks through line distribution and protection for long cables. In normal conditions, the bimetallic contact allows the electrical current to flow through the MCCB. The 140U-LTD3-D40 Trip Unit is temperature-sensitive. After the installation, with the circuit breaker in the tripped position, make sure that the stationary interface barriers are properly installed in the base.