Description
The GE Multilin MMII-PD-1-2-120 (also categorized under the MM2 series) is a microprocessor-based, panel-mounted motor management and protection relay. Engineered primarily for low-voltage AC motors within Motor Control Center (MCC) applications, it integrates protection, local control logic, and real-time diagnostic monitoring into a single chassis. By doing so, it replaces traditional discrete thermal overload elements, timers, and auxiliary relays.
Commercial Availability & Procurement Profile
- Product Line Lifecycle: Legacy / Active Maintenance Phase (OEM production scaled back; primarily supported via certified distribution channels).
- Condition: Available in Factory Sealed (New Surplus) or Refurbished (Fully bench-tested and cleared).
- Warranty: 12-Month Comprehensive Technical Warranty.
- Lead Time: Ships within 24 to 48 hours from central inventory.
- Pricing Note: List prices are indicative and fluctuate based on market availability of legacy electronic components. Contact our technical procurement team for a firm, written quote.
Technical Specifications & Ordering Codes
The model code MMII-PD-1-2-120 designates specific factory-installed options and configurations broken down by the OEM nomenclature:
- MMII / MM2: Motor Manager II Series.
- PD: Panel Mount Design with integrated faceplate, alphanumeric LCD display, and control keys.
- 1: Option Package 1 enabled (Enhanced Control and Diagnostics).
- 2: Option Package 2 enabled (Enhanced Protection and I/O expansion).
- 120: 120 V AC auxiliary control supply voltage.
Hardware & Operating Parameters
| Parameter | Technical Value / Specification |
| Manufacturer | GE Multilin / General Electric |
| Control Voltage Input | 120 V AC nominal (Operating range: 80 to 135 V AC), 50/60 Hz |
| Power Consumption | Maximum 30 VA |
| Fixed Digital Inputs | 6 dedicated control inputs (Start A/B, Stop, Isolator status) |
| Programmable Digital Inputs | 10 process interlock inputs |
| Analog Interfaces | 1 × 4–20 mA input channel; 1 × single-phase VT input (for kW/kWh calculation) |
| Output Relays | 2 × Contactor Control (A and B) + 2 × Auxiliary Programmable Relays |
| Contact Rating | 10 A at 250 V AC resistive, 1/3 HP at 125/250 V AC inductive |
| Serial Communication | RS-485 port supporting Modbus RTU protocol (1,200 to 19,200 bps) |
| Operating Temperature | 0 to +60°C (+32 to +140°F) |
| Weight / Form Factor | 1.36 kg (3.0 lbs) / Panel flush-mount chassis |
Protection & Control Architecture
The inclusion of Option Packages 1 and 2 expands the standard protection array into a highly sophisticated diagnostic suite.
Protection Suite
- Thermal Overload: Employs a dynamic I^2t thermal model utilizing 12 selectable overload curves (8 standard industrial curves and 4 NEMA-compatible variants). Trip accuracy tracks within \pm200 ms for rapid faults under 10 seconds.
- Phase Dynamics: Phase unbalance tracking, phase loss/reversal protection, and rapid phase-imbalance alarming to prevent stator overheating.
- Rotor & Mechanical Faults: Locked/stalled rotor detection, undercurrent/underpower protection (ideal for detecting loss-of-prime in pump applications), and direct thermistor input supporting NTC/PTC sensors for motor winding overtemperature tracking.
- Electrical Monitoring: Integrated ground fault zero-sequence sensing along with overvoltage and undervoltage parameters.
Control Capabilities
The relay natively supports diverse starter configurations configured directly through the EnerVista MMII software package or the front keypad:
- Full-Voltage Non-Reversing (FVNR) & Full-Voltage Reversing (FVR)
- Wye-Delta (Y-\Delta) reduced-voltage starters
- Two-Speed motor controls and variable frequency drive (VFD) interfacing
- Configurable undervoltage auto-restart sequence to safely ride through brief line voltage dips.
Field Interfacing & Integration Constraints
When deploying the MMII-PD-1-2-120 in an active environment or swapping out an older MMII unit, engineers must account for the following architectural constraints:
- Ground Fault CT Selection: The ground fault protection input requires a specific zero-sequence Current Transformer (typically a 50:0.025 ratio sensor). Standard 5 A secondary CT outputs cannot be wired directly into the ground fault terminal without destroying the low-level input sensing circuit.
- Modbus Network Termination: When linking multiple units over an RS-485 multi-drop daisy chain for SCADA integration, ensure the final unit in the physical segment has a 120\ \Omega terminating resistor placed across the line to suppress communication reflections.
- NVRAM / History Preservation: Pre-trip historical data and motor operation statistics are stored in non-volatile memory. If retrofitting a device or swapping units, manually log runtime counters and historical fault logs from the old unit via the EnerVista software to preserve plant maintenance history.
Field Engineering Note: When configuring the thermal overload settings, ensure you input the exact Motor Service Factor (SF) alongside the Full Load Amps (FLA). The internal thermal algorithm multiplies the FLA by the programmed SF boundary; setting this incorrectly will either cause nuisance tripping during normal heavy loads or fail to trip during sustained, damaging overloads.
