Siemens BQD320 Circuit Breaker (277/480VAC, 20A, 3P)

These BQD series miniature circuit breakers are bolted into place in panelboards, so they're more stable than plug-in breakers. They interrupt currents when low-level faults are detected in the circuit. They have a lug orientation to allow for straight-in wiring through bus bars, which eliminates the need to pigtail wires and helps organize the panelboard.