The ABB SPAJ 141C-AA​ is a versatile, combined numerical protection relay manufactured by ABB, designed for comprehensive overcurrent and earth-fault protection of electrical feeders, motors, transformers, and generators in medium-voltage (MV) and low-voltage (LV) networks. This relay integrates two essential protection functions—phase overcurrent and sensitive earth-fault—into a single, compact unit, providing a cost-effective and reliable solution for primary and backup protection in industrial and utility electrical systems.

In a manufacturing plant’s main 6kV switchgear, each outgoing feeder powering a critical production line requires protection against phase-to-phase and phase-to-ground faults. The ABB SPAJ 141C-AA​ relay is installed on each feeder cubicle. It continuously monitors the three phase currents and the neutral/earth-fault current. During normal operation, it displays real-time current values. If a downstream cable fault causes a sudden, sustained overcurrent, the relay’s phase overcurrent function activates. Using a selected inverse-time curve (e.g., EI, VI), it calculates the precise trip time, coordinating with upstream and downstream relays to isolate only the faulty feeder, preventing a total plant blackout. Simultaneously, its sensitive earth-fault function can detect low-magnitude insulation failures, providing an early warning alarm before a fault escalates. The SPAJ 141C-AA​ acts as the intelligent sentry, ensuring electrical faults are cleared selectively to maintain maximum power availability for healthy plant sections.