The Allen-Bradley 140U-K3X3 UL Molded Case Circuit Breaker is a K-Frame breaker frame that is designed for overload and short-circuit protection of a wide range of control panel applications. The K-Frame circuit breakers have a very small footprint, making them ideal for limited panel space applications. They support back-feeding at 240, 480, or 277 Volts AC, and they are used in applications like feeder circuits, small cabinets, distribution panels, branch circuit protection, heaters, air conditioning, refrigeration, and high-intensity discharge applications (HID lamps). The 140U-K3X3 Circuit Breaker is a 3-pole circuit breaker frame with a 400 Amps current rating and a 35 Kilo-Amps maximum breaking capacity rating. It supports circuits with a 240 Volts AC to 600 Volts AC voltage supply range, and it has an insulation voltage rating of 750 Volts.

The 140U-K3X3 Circuit Breaker has a mechanical lifespan rating of 100,000 operations, and it also has an electrical life cycle of 10,000 operations. The 140U-K3X3 Circuit Breaker has no factory-installed internal modules, but modules like the shunt-trip, auxiliary contact, under voltage release, and alarm contacts can be installed easily within the frame. Likewise, trip unit units of various types (Fixed Thermal/Fixed Magnetic, Fixed Thermal/Adjust Magnetic, Adjust Thermal/Fixed Magnetic, Adjust Thermal/Adjust Magnetic, Electronic LS, etc.) can be installed within the frame. The 140U-K3X3 Circuit Breaker also supports a long list of external accessories. This breaker frame supports mounting in a control panel enclosure, and it has a rated operating temperature limit of 60 degrees Celsius. It has an open enclosure type design, and it supports installation at a maximum altitude of 2000 meters (6000 feet) without de-rating.