MERLIN GERIN STR 58U Electronic Trip Unit

Overview

The MERLIN GERIN STR 58U is a universal electronic trip control unit for the Merlin Gerin Masterpact MP air circuit breaker platform. It is the high-end universal protection variant within the STR family, alongside STR28D and STR38S. It provides fully adjustable long‑time, short‑time, instantaneous and earth‑fault protection, plus metering, harmonic monitoring and event logging. It is widely deployed on low‑voltage main incoming panels, generator feeders and large industrial MCC power distribution skids. This legacy unit is discontinued and only supplied as spare replacement.

Features

The MERLIN GERIN STR 58U supports universal selective protection for Masterpact MP series breakers.STR 58U offers four main protection curves: long‑time overload, short‑time delay, instantaneous short‑circuit and ground‑fault protection. Self‑powered via current sensors for protection functions; optional 24 VDC auxiliary supply for display and communication. Built‑in fault trip indicator with local reset button. Supports zone selective interlocking (ZSI) for upstream and downstream selectivity coordination. Integrated metering: current measurement, harmonic distortion recording and fault event history storage. Rating plug configurable to match the breaker sensor nominal current. Compliant with IEC 60947‑2, designed for 50/60 Hz low‑voltage distribution systems.

Specs

Device Type: Electronic Trip Control Unit Model: MERLIN GERIN STR 58U Brand: Merlin Gerin (Schneider Electric) Series: STR trip unit for Masterpact MP Protection: L, S, I, G earth fault Power supply: Self‑powered for protection; 24 VDC optional auxiliary supply for display / communication Function: Protection, metering, event log, ZSI Status: Discontinued legacy trip unit, spare part only

Principle

The MERLIN GERIN STR 58U samples current signals from the breaker’s current transformers. It continuously compares measured values against the configured protection thresholds. When an overcurrent or earth‑fault condition exceeds the setting, the trip unit sends a release signal to the breaker operating mechanism to open the main contacts. It also records fault data and makes measurements available for local display or remote communication.

Applications

The MERLIN GERIN STR 58U is fitted on Masterpact MP air circuit breakers for main incoming switchgear, transformer secondary protection, generator paralleling panels and heavy industrial distribution skids. The MERLIN GERIN STR 58U is stocked as spare replacement for legacy Merlin Gerin low‑voltage switchgear systems.