The 4NK0AJ is a thermal overload relay from Fuji Electric's "Orange Line" series designed to provide motor overload protection in industrial applications. It features a 1NO+1NC alarm contact with automatic reset capability, a built-in heater for accurate operation, and an open-phase protection device. The relay includes a calibrated rated current dial and manual trip device, with ambient temperature compensation that limits ampere value changes to approximately 10% between -5°C and 40°C. The alarm contact is rated for continuous operation at 2.5 A with current-make/break ratings of 15/1.5 A at 110-120V, 7.5/0.75 A at 220-240V, 3.75/0.375 A at 440-480V, and 3.0/0.3 A at 550-600V. This relay is ideal for protecting motors and electrical equipment from overload conditions while maintaining reliable performance across varying ambient temperatures.