4NK0AM is a thermal overload relay with open-phase protection designed for use with AC contactors in motor starter applications. It features a built-in heater for accurate operation, a calibrated rated current dial with adjustable ampere ranges (0.1–2.6 A depending on frame size), and 1NO+1NC alarm contacts with automatic reset capability. The relay operates with a pick-up voltage of 9 V and drop-out voltage of 58–73 V, with contact operating times of 9–20 ms for coil ON and 5–16 ms for coil OFF. It includes an ambient temperature compensator that limits ampere value changes to approximately 10% as ambient temperature varies between -5°C and 40°C, and provides manual trip and open-phase protection devices. These relays are commonly used in industrial motor control circuits to protect motors from overload conditions and phase loss, ensuring reliable equipment operation and personnel safety.