Overview
The General Electric 121AC51B1A is an IAC series time-overcurrent relay designed for protective functions in industrial and utility power distribution systems. This unit is in used condition and has been inspected for functionality. The 121AC51B1A delivers reliable overcurrent detection and time-delay operation for coordinated protection of AC circuits.
Key Features
- Single-phase, non-directional overcurrent protection for AC systems
- Adjustable time-dial and current-tap settings for flexible coordination
- Induction disc time mechanism with mechanical target for reliable operation
- Available with multiple time-current characteristics for application flexibility
- Proven IAC series design for industrial protection
Technical Specifications
- Relay Type: IAC Time-Overcurrent Relay
- Model: 121AC51B1A
- Function: Time-overcurrent protection (phase or ground)
- Operating Mechanism: Magnetic core coil with induction disc
- Mounting: Panel-mount (vertical surface recommended)
- Contact Rating: 30 A maximum at 250 V
- Phase Configuration: Single-phase
- Condition: Used, tested
Typical Applications
This relay is commonly used for:
- Protection of industrial feeders and transmission lines
- Motor and transformer overload protection
- Coordination with circuit breakers and fuses in medium-voltage switchgear
- Phase and ground fault detection in AC power systems
- Legacy protection systems in utilities and industrial plants
Compatibility & Replacements
Compatible With
- Industrial AC power distribution systems
- Utility protection schemes with current transformers (CTs)
- Medium-voltage switchgear and control panels
- Legacy and modern protection coordination schemes
Replaces / Drop-In Replacement For
Verify compatibility with your system integrator or electrical engineer before ordering. Similar GE IAC series models (121AC51B, 12IAC51B series) may have compatible footprints, but direct replacement confirmation is required based on your specific control circuit and CT secondary ratings.
Works With
- GE current transformers (CTs) and instrument transformers
- Industrial control panels and protection relays
- AC protection schemes with time-delayed coordination
- ANSI/IEEE standard protection systems
