Protect Networks from Ground Faults with ABB SPAJ 140C-AA Relay

In a 10kV industrial plant distribution network, a cable feeding a critical production process develops an insulation weakness. A small, intermittent earth leakage current begins to flow. Without sensitive detection, this fault could escalate, causing a phase-to-ground short circuit that damages the cable, trips the main feeder breaker, and shuts down the entire line. The ABB SPAJ 140C-AA​ relay is installed on this feeder. It continuously monitors the residual current (the vector sum of the three-phase currents, Io) via a core balance current transformer (CBCT) encircling the cable. The highly sensitive relay detects the low-level earth leakage current (e.g., 5-20% of full load) almost immediately. Depending on its setting, it can issue an early warning alarm, allowing maintenance to locate and plan repair, or after a time delay, trip the feeder circuit breaker to isolate the fault before it causes major damage. It directly addresses the key pain points of unplanned outages and equipment damage by providing the earliest possible warning of insulation degradation.