ABB PR121/P-LSIG Electronic Trip Unit

Overview

The ABB PR121/P-LSIG is an electronic overcurrent trip unit designed for the ABB SACE Emax air circuit breaker series. This PR121/P-LSIG provides full LSIG protection functions: long time overload protection, short time delay short-circuit protection, instantaneous short-circuit protection and ground fault protection. It adopts microprocessor-based measurement technology, responds to true RMS current, and requires no external auxiliary power supply for normal protection operation. It is widely used for main incoming feeders, bus tie and heavy load feeder protection in low-voltage switchgear, process skids, power distribution and industrial automation systems. It is a direct drop-in replacement trip unit for Emax circuit breakers.

Features

The ABB PR121/P-LSIG is a basic electronic trip unit for SACE Emax ACBs.PR121/P-LSIG integrates complete LSIG protection curve adjustment via DIP switches. True RMS current sensing ensures stable measurement under distorted load current. Self-powered from current transformers, protection works without external 24V auxiliary supply. Adjustable long time pickup, short time pickup, instantaneous pickup and ground fault pickup thresholds. Trip cause indication and basic fault memory for troubleshooting. Neutral pole protection setting configurable: OFF, 50%, 100% or 200% of phase current. Modular plug-in structure, easy on-site replacement without dismantling the breaker main body. Compatible with the full ABB SACE Emax range including E1, E2, E3, E4 and E6 frames. Compliant with IEC 60947-2, UL 1066, CE and relevant low-voltage distribution 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 via built-in CTs Setting method: DIP switch Compatible 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 current through the breaker internal current transformers. The microprocessor compares the measured RMS current against 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 retains the last trip information for fault analysis.

Applications

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