SCA / SCB / SCCÂ Short Circuit (Start-up) fault in Toshiba drive
SCA / SCB / SCC Short Circuit (Start-up) fault in Toshiba drive
Description While "OC" (Overcurrent) typically happens while running, the SC (Short Circuit) family of faults usually occurs the instant the "Run" command is given, before the motor even moves. The drive performs a diagnostic pulse; if it detects extremely low impedance (a dead short) on the output terminals, it trips SCA (Short Phase U), SCB (Short Phase V), or SCC (Short Phase W). This is a faster protection mechanism than OC. Causes
1. Wiring Error: A phase wire is inadvertently touching the ground or another phase inside the motor junction box.
2. Locked Rotor: The motor is mechanically welded shut or the load is completely immovable.
3. IGBT Shoot-Through: The internal drive transistors have failed in a "Short" state.
4. Cable Capacitance: On extremely long cable runs, the instantaneous charging current of the cable capacitance can look like a short circuit to the sensitive detection circuit. Solution Disconnect power immediately. This is a high-current fault.
Remove the motor leads (U, V, W) from the drive. Use a multimeter to measure continuity between the drive output terminals (U-V, V-W, W-U). You should read high resistance (Mega-ohms) or an open diode drop. If you read 0 ohms between any two terminals on the drive itself, the IGBT module is blown, and the drive needs repair.
If the drive measures okay, test the motor cable and windings. A standard multimeter might show continuity (low ohms) for a motor winding, which is normal, but it should not show 0.00 ohms. Use a Megger to check for Phase-to-Phase shorts (if your megger supports it) or Phase-to-Ground.
If the cabling is very long (>200m), you may need to reduce the carrier frequency or install an output dV/dt filter to suppress the capacitive inrush current that triggers the SC sensor.
Description While "OC" (Overcurrent) typically happens while running, the SC (Short Circuit) family of faults usually occurs the instant the "Run" command is given, before the motor even moves. The drive performs a diagnostic pulse; if it detects extremely low impedance (a dead short) on the output terminals, it trips SCA (Short Phase U), SCB (Short Phase V), or SCC (Short Phase W). This is a faster protection mechanism than OC. Causes
1. Wiring Error: A phase wire is inadvertently touching the ground or another phase inside the motor junction box.
2. Locked Rotor: The motor is mechanically welded shut or the load is completely immovable.
3. IGBT Shoot-Through: The internal drive transistors have failed in a "Short" state.
4. Cable Capacitance: On extremely long cable runs, the instantaneous charging current of the cable capacitance can look like a short circuit to the sensitive detection circuit. Solution Disconnect power immediately. This is a high-current fault.
Remove the motor leads (U, V, W) from the drive. Use a multimeter to measure continuity between the drive output terminals (U-V, V-W, W-U). You should read high resistance (Mega-ohms) or an open diode drop. If you read 0 ohms between any two terminals on the drive itself, the IGBT module is blown, and the drive needs repair.
If the drive measures okay, test the motor cable and windings. A standard multimeter might show continuity (low ohms) for a motor winding, which is normal, but it should not show 0.00 ohms. Use a Megger to check for Phase-to-Phase shorts (if your megger supports it) or Phase-to-Ground.
If the cabling is very long (>200m), you may need to reduce the carrier frequency or install an output dV/dt filter to suppress the capacitive inrush current that triggers the SC sensor.
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