Square D QOB3901021 Three Pole Circuit Breaker

The Square D QOB3901021 is a 90 A, three‑pole bolt‑on miniature circuit breaker engineered for 120/240 V AC service, delivering a 10 kA interrupt rating to quickly clear faults on three‑phase feeders and branch circuits in commercial or light‑industrial panels. As part of the Square D QO family, this QOB model provides thermal‑magnetic overcurrent protection and uses a bolt‑on mounting (QOB) for panelboard compatibility, with AC shunt‑trip capability that enables remote disconnection when required by safety interlocks or automation protocols. The device is designed for panelboards and switchgear that demand reliable three‑phase protection and convenient field installation, with a 90 A continuous rating suitable for feeders and control circuits and a 240 VAC operating range aligned with common industrial distribution schemes. Ideal applications include commercial electrical distribution, equipment controllers, motor circuits, and other 3‑phase loads where remote‑trip capability is beneficial, and it fits Square D enclosures and accessories designed for QO/QOB breakers to ensure proper mounting, labeling, and coordinated protection across the installation.