Schneider Electric's Square D S33661 Shunt Trip is a remote-control trip accessory for compatible Square D breakers, providing an externally triggered trip coil for emergency shutdown. It mounts on or is wired into breaker accessory terminals and accepts a control signal from a remote switch, PLC, or automation output, with a typical control voltage of 120 V AC (verify the specific model rating). Used in motor control centers, generator transfer switches, fire/safety shutdown circuits, and remote equipment protection systems where remote tripping is required. Common replacements include Square D S33662, Square D 8881ST, and Schneider Electric QO.
