Siemens CQD340 DIN Rail Mounted Circuit Breaker

Siemens CQD340 is a three‑pole molded‑case circuit breaker designed for DIN‑rail mounting in low‑voltage distribution panels. It is rated for 40 A at 277/480 VAC (three‑phase), with a 14 kA short‑circuit interrupting capacity, and uses a thermal‑magnetic trip mechanism to protect feeders from overload and faults. The CQD340 belongs to Siemens' CQD family (Cable‑In/Cable‑Out) and features DIN rail mounting with box‑lug termination and cable‑in/cable‑out wiring options, suitable for compact panel layouts. Termination supports 14–6 AWG copper or 12–6 AWG aluminum conductors, depending on wiring method, making it flexible for common field wiring. Typical applications include protection of branch circuits, motor feeders, lighting panels, and commercial/industrial distribution where a 40 A protection level is appropriate. The device's design emphasizes quick, reliable tripping at fault conditions while fitting standard DIN rails for streamlined installation in existing enclosures, achieving dependable performance in 50/60 Hz power environments.