UCÂ Undercurrent / Low Current Detection fault in Toshiba drive
UC Undercurrent / Low Current Detection fault in Toshiba drive
Description The UC fault indicates that the motor current has dropped below a user-defined threshold for a specific amount of time while the drive is running. Unlike Overcurrent (which protects the drive), Undercurrent is an application protection feature designed to save the mechanical system. It essentially means "The motor is spinning, but it isn't doing any work." This is critical in pumping applications (to prevent cavitation or running dry) and HVAC (to detect broken belts). Causes
1. Pump Dry Run: The intake tank is empty, or there is an airlock in the pipe. The impeller spins freely in air, drawing very little current.
2. Broken Transmission: A drive belt has snapped, or a shaft coupling has sheared. The motor is spinning unconnected to the load.
3. Closed Valve: A discharge valve is completely closed (dead-heading), reducing the work done by a centrifugal pump.
4. Oversized Motor: The motor is too large for the application, so the normal running current is naturally below the default detection threshold.
5. Parameter Setup: The UC trip level is set too high (e.g., set to 80% of FLA when the normal load is only 60%). Solution Start by inspecting the mechanical load. If this is a fan application, visually confirm the belts are intact and tight. If it is a pump, check the suction line pressure/level. Do not simply reset and run a pump with a UC fault, as running a pump dry will destroy the mechanical seals within minutes due to friction heat.
If the mechanics are sound and the process is normal (e.g., the pump is moving fluid), check the drive parameters. You need to monitor the actual amperage on the keypad while the system is running normally. Compare this value to the "Low Current Detection Level" (often parameter F611 or similar). If your system normally runs at 4.5 Amps, but the trip level is set to 5.0 Amps, it will trip falsely. Adjust the parameter to be roughly 80% of your actual running amps.
You can also adjust the "Low Current Detection Time" (delay). If the system naturally has low load during startup or specific cycles, increase the delay (e.g., from 2 seconds to 10 seconds) to filter out transient low-load conditions without disabling the protection entirely.
Description The UC fault indicates that the motor current has dropped below a user-defined threshold for a specific amount of time while the drive is running. Unlike Overcurrent (which protects the drive), Undercurrent is an application protection feature designed to save the mechanical system. It essentially means "The motor is spinning, but it isn't doing any work." This is critical in pumping applications (to prevent cavitation or running dry) and HVAC (to detect broken belts). Causes
1. Pump Dry Run: The intake tank is empty, or there is an airlock in the pipe. The impeller spins freely in air, drawing very little current.
2. Broken Transmission: A drive belt has snapped, or a shaft coupling has sheared. The motor is spinning unconnected to the load.
3. Closed Valve: A discharge valve is completely closed (dead-heading), reducing the work done by a centrifugal pump.
4. Oversized Motor: The motor is too large for the application, so the normal running current is naturally below the default detection threshold.
5. Parameter Setup: The UC trip level is set too high (e.g., set to 80% of FLA when the normal load is only 60%). Solution Start by inspecting the mechanical load. If this is a fan application, visually confirm the belts are intact and tight. If it is a pump, check the suction line pressure/level. Do not simply reset and run a pump with a UC fault, as running a pump dry will destroy the mechanical seals within minutes due to friction heat.
If the mechanics are sound and the process is normal (e.g., the pump is moving fluid), check the drive parameters. You need to monitor the actual amperage on the keypad while the system is running normally. Compare this value to the "Low Current Detection Level" (often parameter F611 or similar). If your system normally runs at 4.5 Amps, but the trip level is set to 5.0 Amps, it will trip falsely. Adjust the parameter to be roughly 80% of your actual running amps.
You can also adjust the "Low Current Detection Time" (delay). If the system naturally has low load during startup or specific cycles, increase the delay (e.g., from 2 seconds to 10 seconds) to filter out transient low-load conditions without disabling the protection entirely.
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