The GEC Alsthom MMLG01 (Part Number 478050G) is a specialized test block designed to provide a safe and reliable interface for the secondary testing of protection relays without disconnecting the primary wiring or risking open-circuiting current transformers.
Product Parameters (Datasheet)
- Model Number: MMLG01
- Part Number: 478050G
- Type: Test Block (MMLG Series)
- Number of Circuits: 14 independent circuits
- Rated Current: 20A continuous (standard for MMLG series)
- Rated Voltage: 300V AC/DC
- Insulation Resistance: >100M Ohms at 500V DC
- Mounting: Panel mount / Flush mount (Size A1 or equivalent)
- Compatible Test Plug: MMLB01 (Multi-finger test plug)
- Housing Material: Flame-retardant molded phenolic or equivalent technical plastic
Country of Origin
This protection accessory was manufactured in the United Kingdom by GEC Alsthom (a legacy brand that evolved through AREVA T&D and Alstom Grid to GE Renewable Energy).
Application Fields
The MMLG01 is an essential component in substation control and protection panels, used in:
- Current Transformer (CT) Circuits: Safely shorting CTs before testing to prevent high-voltage spikes.
- Voltage Transformer (VT) Circuits: Isolating potential circuits for calibration.
- Tripping Logic Testing: Monitoring or injecting signals into trip circuits.
- Substation Commissioning: Providing a centralized point for secondary injection testing.
Product Usage Instructions
- Preparation: Ensure you have the matching MMLB test plug prepared for the specific circuits you intend to monitor.
- Insertion: Insert the MMLB test plug into the MMLG01 block. The design ensures that CT secondary circuits are short-circuited before they are disconnected from the relay, preventing dangerous open-circuits.
- Testing: Perform secondary injection or monitoring via the terminals on the test plug.
- Removal: Once testing is complete, remove the test plug. The internal spring contacts of the MMLG01 will automatically restore the original connections between the system and the relay.
- Safety Note: Always verify the “CT shorting” finger positions on your test plug before inserting it into a live circuit.
Product Technical Description
Technically, the MMLG01 is a multi-pole connector with internal “make-before-break” or automatic shorting features. When no plug is inserted, the internal contacts bridge the rear terminals to complete the circuit between the external wiring and the protection relay. When a test plug is inserted, these internal bridges are diverted through the plug. This modular design eliminates the need for manual link removal and significantly reduces the risk of human error during routine maintenance of complex protection schemes.
Q&A (Common Questions)
Q: Does the MMLG01 have an internal flag or alarm? A: No, the MMLG01 is a passive interface block. It does not have electronic logic; it provides physical access to the relay circuits.
Q: Can I use an MMLB01 plug from a different manufacturer? A: The MMLG and MMLB series are standardized designs originally by GEC Alsthom. While Alstom or GE versions are typically identical, always check for physical alignment before full insertion.
Q: What happens if I insert the plug upside down? A: The MMLG01 and its associated plugs are keyed or designed with specific offset features to prevent incorrect orientation.
Q: Are all 14 circuits the same? A: Yes, the MMLG01 typically features 14 identical circuits, but the user defines how they are used (e.g., for CTs, VTs, or DC supplies) during panel wiring.
Similar Model Recommendations
- GEC Alsthom MMLG02 (Alternative terminal/circuit configuration)
- GEC Alsthom MMLB01 (Matching 14-finger test plug)
- GEC Alsthom MMLG03 (Compact version)
- Alstom MVAJ (Associated tripping relays often used in the same panels)
- GE METI (Modern digital equivalent for test interfaces)
Find more details on the GEC Alsthom MMLG01 and explore our complete inventory of protection and control accessories.
