Field engineers and system designers who need a practical, no-nonsense reference.
| Fault Type | Cause | Primary Protection | | :--- | :--- | :--- | | | Severe insulation failure | Instantaneous overcurrent (50) | | Line-to-Line | Fallen wires, damaged cables | Overcurrent (51) | | Line-to-Ground | Tree branches, moisture, human contact | Ground fault relay (50G/51G) | | Overload | Too many loads, failing motor | Thermal overload (49) / Long-time pickup | | Arc Flash | Ionized air from gaps | Arc flash detection (light + current) | electrical distribution system protection pdf