The ABB PR121/P is a digital electronic trip unit designed for use in ABB SACE Emax low‑voltage air circuit breakers. It provides adaptive and adjustable protection against multiple types of overcurrent faults in three‑phase AC power distribution systems. The PR121/P trip unit integrates easily into compatible breakers and allows the user to configure protection settings via front‑panel DIP switches or interface LEDs. It is suitable for use in industrial and commercial electrical panels to protect circuits against overload, short‑time faults, instantaneous short circuits, and optionally ground faults. It is typically paired with breakers rated for In = 1250 A and is often powered by a 220–240 V AC auxiliary/control supply for its internal electronics and signaling functions.
