Et / OH2 / E-18 External Thermal Trip (PTC) fault in Toshiba drive
Et / OH2 / E-18 External Thermal Trip (PTC) fault in Toshiba drive
Description This fault comes from a specialized input. Many large or hazardous-duty motors have embedded thermal sensors (Thermistors or PTCs) inside their windings. These are wired back to the VFD. If the motor windings get too hot physically (regardless of current draw), the resistance of the sensor spikes, and the drive trips "Et" or "OH2". This protects the motor in scenarios where current is normal but cooling is blocked (e.g., motor covered in sawdust). Causes
1. Actual Overheat: The motor is physically too hot to touch.
2. Clogged Cooling Fins: The motor fan is blocked, or the ambient temperature is too high.
3. Wiring Short/Open: The thin wires coming from the motor thermistor are fragile and often break or short to the conduit.
4. Logic Conflict: A digital input terminal (like S3) is programmed for "External Thermal" (Et) but nothing is connected to it. Solution Check the motor temperature. If it is cool, the fault is in the sensing circuit. Disconnect the thermistor wires at the VFD terminal strip. Measure the resistance of the thermistor with a multimeter. A standard PTC should read between 100 ohms (cold) and a few k-Ohms (hot). If it reads Infinite (Open) or 0 (Short), the sensor inside the motor is damaged.
If the sensor is damaged, you cannot replace it without rewinding the motor. You must disable the "External Thermal Protection" parameter in the drive and rely on the standard "Electronic Thermal Overload" (OL1) based on current calculations.
If you are not using a thermistor but get this fault, check your digital input assignments. Ensure no terminal is inadvertently assigned to "External Trip" or "Et". A floating or unpowered input assigned to this function will cause an immediate trip.
Description This fault comes from a specialized input. Many large or hazardous-duty motors have embedded thermal sensors (Thermistors or PTCs) inside their windings. These are wired back to the VFD. If the motor windings get too hot physically (regardless of current draw), the resistance of the sensor spikes, and the drive trips "Et" or "OH2". This protects the motor in scenarios where current is normal but cooling is blocked (e.g., motor covered in sawdust). Causes
1. Actual Overheat: The motor is physically too hot to touch.
2. Clogged Cooling Fins: The motor fan is blocked, or the ambient temperature is too high.
3. Wiring Short/Open: The thin wires coming from the motor thermistor are fragile and often break or short to the conduit.
4. Logic Conflict: A digital input terminal (like S3) is programmed for "External Thermal" (Et) but nothing is connected to it. Solution Check the motor temperature. If it is cool, the fault is in the sensing circuit. Disconnect the thermistor wires at the VFD terminal strip. Measure the resistance of the thermistor with a multimeter. A standard PTC should read between 100 ohms (cold) and a few k-Ohms (hot). If it reads Infinite (Open) or 0 (Short), the sensor inside the motor is damaged.
If the sensor is damaged, you cannot replace it without rewinding the motor. You must disable the "External Thermal Protection" parameter in the drive and rely on the standard "Electronic Thermal Overload" (OL1) based on current calculations.
If you are not using a thermistor but get this fault, check your digital input assignments. Ensure no terminal is inadvertently assigned to "External Trip" or "Et". A floating or unpowered input assigned to this function will cause an immediate trip.
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