Product Core Brief

• Model: MMLG01
• Brand: ALSTOM / GE Vernova
• Series: Midos-Range Protection Test Block
• Core Function: Standard 14-circuit test block used with multi-finger test plugs to isolate, monitor, and perform secondary injection testing on protection relay circuits without disturbing permanent wiring.
• Product Type: Test Block / Relay Test Terminal Block / Spare Test Access Unit
• Key Specs: 14 independent circuits | Normally-closed internal contact pairs | Multi-finger test plug interface | Panel or DIN-rail adjacent mounting | Compatible with MMLB-series test plugs
• Condition: New Original / New Surplus

Product Introduction

ALSTOM MMLG01 is a standard test block from the Midos-range protection accessory family, now referenced under GE Vernova. It is designed to be mounted adjacent to modular protection relays and provides safe access points for secondary injection testing, circuit monitoring, and temporary isolation of protection wiring.

The block carries 14 circuits, each brought out to separate terminal pairs at the rear. Under normal service, internal spring-loaded contacts remain closed so that protection circuits pass through the block without interruption. When the matching multi-finger test plug is inserted, the corresponding circuit pairs are opened, allowing test sources to be applied without disconnecting field wiring.

MMLG01 is commonly used in feeder, transformer, generator, busbar-adjacent, and general protection panels where relay maintenance, commissioning, or periodic testing is required. It is not a protection relay, PLC, DCS card, or control module. Third-party spare listings sometimes describe it only as a generic ALSTOM spare part without functional detail, so the panel drawing and installed block label should be confirmed before replacement.

Key Technical Specifications

Quality Control Process

• Visual and code check: Confirm MMLG01 labeling, terminal condition, contact springs, and mounting hardware.
• Circuit continuity check: Verify all 14 circuit pairs are closed in normal service position.
• Test plug operation check: Insert MMLB01 test plug and confirm corresponding circuits open correctly.
• Terminal and insulation check: Confirm rear terminal tightness, insulation condition, and no shorted pairs.
• Final packing: Record test results, apply asset labels, and ship with terminal protection.

Replacement Pitfall Guide

❗ Confirm it is a test block, not a relay or controller. MMLG01 is a test access block; it does not perform protection logic, overcurrent calculation, or communication.

❗ Verify circuit count and wiring. The standard MMLG01 carries 14 circuits; replacing it with a different variant may change terminal count or CT/VT access.

❗ Match the correct test plug. MMLG01 is intended for use with MMLB01 multi-finger test plugs; mismatched plugs may not open contacts correctly.

❗ Do not remove the block under live protection duty without a safe work procedure. Opening protection circuits during normal operation can disable tripping or cause unintended isolation.

Keep these in mind and you’ll cut 90% of rework time.

Compatibility Matrix & Benchmarks

• Typical use: Protection relay panels, feeder bays, transformer and generator protection cabinets, commissioning, maintenance, and periodic secondary injection testing.
• Key verification points: MMLG01 label, 14-circuit configuration, rear terminal wiring, MMLB01 test plug availability, and panel test scheme drawing.