ABB PR121/P-LSIG Electronic Trip Unit

Overview

The ABB PR121/P-LSIG is an electronic overcurrent trip unit for the ABB SACE Emax air circuit breaker range. This ABB PR121/P-LSIG delivers complete LSIG protection functions: long-time overload, short-time delay short-circuit, instantaneous short-circuit and ground fault protection. It adopts microprocessor-based true RMS current measurement and is self-powered by the built-in current transformers, so protection does not require an external auxiliary power supply. It is widely used for main incoming feeders, bus tie feeders and heavy-load outgoing circuits in low-voltage switchgear, power distribution skids and industrial automation systems. It serves as a direct replacement spare part for Emax circuit breakers.

Features

The ABB PR121/P-LSIG is the basic electronic release for SACE Emax ACBs.PR121/P-LSIG provides full LSIG protection curves adjustable via DIP switches. True RMS sensing ensures stable measurement under distorted harmonic load currents. Self-powered from internal CTs; protection remains active without external 24V auxiliary supply. Adjustable thresholds for long time pickup, short time pickup, instantaneous pickup and ground fault pickup. Trip indication and basic fault memory for post-fault diagnostics. Neutral pole protection configurable: OFF, 50%, 100% or 200% of phase current. Modular plug-in design, field replacement without dismantling the breaker main body. Compatible with fixed and withdrawable versions of Emax E1, E2, E3, E4 and E6 frames. Compliant with IEC 60947-2, UL 1066, CE and relevant low-voltage switchgear standards.

Specs

Device Type: Electronic Trip Unit Model: ABB PR121/P-LSIG Brand: ABB Series: SACE Emax Protection: L (Long-time overload), S (Short-time delay), I (Instantaneous), G (Ground fault) Measurement: True RMS Power supply: Self-powered by built-in CTs Setting method: DIP switch Applicable breaker: SACE Emax E1/E2/E3/E4/E6 air circuit breaker Status: Genuine ABB low-voltage protection spare part

Principle

The ABB PR121/P-LSIG samples phase and neutral currents through the current transformers integrated inside the breaker. The microprocessor compares measured RMS values with the configured LSIG thresholds. When overload, short-circuit or ground fault conditions are detected, the trip unit sends a trigger signal to the breaker operating mechanism to open the main contacts and isolate the faulty circuit. The unit stores the last trip information for fault analysis.

Applications

The ABB PR121/P-LSIG is fitted to SACE Emax air circuit breakers for main incoming cabinets, bus couplers and motor feeder protection on industrial distribution skids, power plants, chemical plants and water treatment switchgear. The PR121/P-LSIG is stocked as spare replacement for low-voltage switchgear maintenance.