ABB ACS880 Fault 5002 (I2t Overload): Causes & Fixes

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1. Understanding the Severity of ABB ACS880 Fault 5002 in Critical Operations

The sudden appearance of Fault 5002: Overload I2t on an ABB ACS880 drive control panel signifies an immediate shutdown based on the motor's internal thermal model calculation. For site engineers managing high-power, continuous-duty applications—such as large pump stations, heavy-duty mixers, or continuous web lines—this is a high-priority, "red-light" fault. The drive's logic has determined that the motor has experienced a significant thermal stress, integrating current over time (the $I^2t$ principle), that exceeds its calculated thermal capacity, demanding an emergency trip to prevent irreparable motor winding damage.

The root cause is rarely as simple as a prolonged high current. Instead, it often points to a complex interplay between mechanical load, application parameters, and the thermal protection settings within the drive. A failure to diagnose the true source quickly results in costly production downtime. The technician’s immediate objective is not just to clear the fault but to understand why the drive’s thermal model registered an overload condition.

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2. The I2t Thermal Model: Motor Protection Philosophy

The ACS880 drive utilizes a sophisticated thermal model to estimate the motor winding temperature, a feature that distinguishes it from simpler protection circuits. This model is essentially a virtual thermometer based on the $I^2t$ principle, where the current ($I$) squared multiplied by the time ($t$) provides a measure of thermal energy injected into the motor.

The drive uses the motor’s nameplate data, entered into parameter group 99 during commissioning, to establish a baseline for its thermal time constant.

Key Motor Thermal Parameters (Group 99 & 35)	Technical Explanation for Field Engineers
99.06 Motor Nom Current	The fundamental baseline for all thermal calculations. If this is incorrectly entered (e.g., lower than actual nameplate), the drive will trip prematurely.
99.07 Motor Nom Freq	Used in calculating slip and the low-speed cooling capacity. Inaccurate input can lead to false I2t trips at lower speeds.
35.55 Motor thermal time constant	Defines how quickly the motor is assumed to heat up and cool down. A shorter time constant (e.g., for a Class 10 trip curve, around $350s$) results in a faster trip under overload conditions. This parameter is critical for matching drive protection to the motor’s actual thermal design.
35.52 Zero speed load	The percentage of rated current the motor can withstand at zero speed without overheating. Essential for motors with little or no self-cooling (e.g., non-blower-cooled motors) in low-speed or holding applications.

Motor Thermal Protection Decision Flowchart

If an engineer faces a persistent Fault 5002, the following conditional logic must be applied before simply clearing the fault:

• Condition: Is the application a constant torque load (e.g., conveyor or extruder) running frequently below $10 \text{ Hz}$?
• Action: Verify the motor has forced ventilation (blower). If not, reduce the load or ensure parameter 35.52 (Zero speed load) accurately reflects the motor's actual low-speed capability, which is often significantly lower than $100\%$. The motor’s self-cooling fan becomes ineffective at low speeds.
• Condition: Did the fault occur immediately following a heavy acceleration cycle?
• Action: Increase the acceleration time in parameter group 23 (Speed reference ramp). A longer ramp rate reduces the peak current draw, lessening the instantaneous accumulation of $I^2t$.
• Condition: Has the motor recently been re-wired or replaced, or is the existing wiring extremely long?
• Action: Verify the motor connection (Delta/Star) matches the drive's parameter settings and the motor’s nameplate. Check the motor cable length against the drive manual's maximum limits, as excessive length increases capacitance and leakage current, potentially contributing to the I2t calculation.

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3. On-Site Troubleshooting and Diagnostics Checklist

A methodical, step-by-step approach is crucial for diagnosing Fault 5002 in a live industrial setting. Simply resetting the fault without resolution will only lead to an immediate recurrence and lost production time.

3.1. Immediate Physical and Environmental Inspection

The fault code itself is an internal calculation, but the cause is almost always external to the drive control unit.

• Physical Motor Check: Immediately check the motor casing temperature (use a non-contact thermometer if available). Is the temperature significantly above the nameplate rating (e.g., $105^\circ \text{C}$ or $130^\circ \text{C}$ for Class F or H)? A hot motor validates the I2t trip. A cold motor suggests a false trip, often a parameter error.
• Cooling System Verification: Confirm that the motor’s cooling fan (if present) is operational and that the air intake/fins are not clogged with dust, dirt, or debris. Restricted airflow is a common hidden cause of genuine thermal overload.
• Mechanical Resistance: Attempt to rotate the motor shaft (if safe and possible). Is the load unusually stiff? Look for signs of bearing failure, gearbox seizure, or a process blockage that is mechanically forcing the motor to draw excessive current.

3.2. Drive Parameter and Event Log Analysis

The ACS880’s control panel and the Drive Composer PC tool are the primary diagnostic instruments.

• Event Log Review (03.05 to 03.07): Access the drive's event log to check for preceding or simultaneous warnings (e.g., A2A1 Cooling Drive module temperature excessive) or other faults (e.g., F0042 Overcurrent). The fault history provides a timeline of the thermal buildup.
• Parameter 35.15 (Motor Temperature %): This parameter shows the estimated motor thermal load percentage at the moment of the trip. A value of $100\%$ confirms the drive's thermal model tripped the unit. A value below $100\%$ immediately prior to the fault suggests a potential sensor issue (if external sensors are used) or a control board malfunction, though this is rare.
• Parameter 35.55 (Motor Thermal Time Constant): Cross-reference this value with the motor manufacturer’s specification or the required NEMA overload class. An aggressive (short) time constant in this parameter can lead to nuisance trips.

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4. Advanced Diagnostics: Distinguishing Real Overload from Nuisance Trips

Troubleshooting Fault 5002 requires the engineer to determine if the trip is due to an actual, dangerous overload condition or a misconfigured, "nuisance" trip.

Scenario	Primary Field Observation	Root Cause Diagnosis and Corrective Action
Real Overload (Mechanical)	Motor current (measured via an external clamp meter) is consistently $>100\%$ of rated current under normal conditions. Motor casing is noticeably hot.	Cause: Increased mechanical friction, product overload, or mechanical damage. Action: De-rate the process, physically clear the mechanical blockage, or replace/repair damaged couplings/bearings.
Real Overload (Environmental)	Drive is installed in a high-ambient temperature environment (e.g., $>40^\circ \text{C}$) or the drive/motor cooling fins are heavily fouled.	Cause: Reduced thermal dissipation capacity for both drive and motor. Action: Improve ventilation, clean drive heatsink and motor fins. Ensure the current limit is derated if the ambient temperature is persistently high.
Nuisance Trip (Parameter Error)	Motor is only mildly warm, or the fault occurs during low-speed, high-torque operations.	Cause: Incorrect motor nameplate data (Group 99), or the 35.55 (Motor thermal time constant) is too aggressive for the application. Action: Re-enter all Group 99 data precisely from the motor nameplate. If necessary, slightly increase $35.55$ to match a Class 20 or Class 30 thermal curve, but only after consultation with motor specifications.
Nuisance Trip (Sensor Mismatch)	Drive is using external temperature sensors (e.g., Pt100) via parameter 35.11 (Temperature 1 source), but the sensor is faulty or incorrectly wired.	Cause: Faulty sensor providing an artificially high temperature reading to the drive's logic. Action: Change 35.11 back to Estimated Temperature (to rely on the I2t model) and replace the external sensor/wiring.

4.1. The Critical Role of the Motor Thermal Time Constant

The parameter 35.55 is the key adjustment point for an engineer dealing with recurring Fault 5002, especially in applications with long-duration peak loads.

• Class 10 Protection: Requires a trip in $\le 10$ seconds at $600\%$ overload. Corresponds to a thermal time constant of approximately $350 \text{ seconds}$. This is the most sensitive setting, typically used for motors in frequent start/stop or cycling applications.
• Class 20 Protection: Requires a trip in $\le 20$ seconds at $600\%$ overload. Corresponds to a thermal time constant of approximately $700 \text{ seconds}$. This is a common intermediate setting for general industrial use.

An experienced technician will determine that if the motor is correctly sized and the trip is only occurring during a temporary, expected peak load, the thermal time constant may need to be increased from the factory default to match a less sensitive protection class (e.g., moving from Class 10 to Class 20) to allow for temporary overload tolerance without compromising motor safety.

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5. Integrating Motor Nameplate Data for Precise Thermal Modeling

For the ACS880's thermal model to function as a reliable guardian, the manual entry of motor nameplate parameters must be executed with zero error. The motor's thermal characteristics are deeply tied to its physical design, which the drive must emulate.

5.1. Data Verification Checklist for Parameter Group 99

Technical staff should treat the initial setup of Group 99 parameters as a prerequisite for stable operation.

1. 99.06 Motor Nom Current ($I_n$): This value must be the RMS motor nameplate current. If the application is running an older motor, the technician should physically measure the actual no-load current and compare it to the theoretical value. A mismatch suggests a wiring fault or mechanical binding that must be resolved before proceeding.
2. 99.10 Motor Nom Power ($P_n$): The power rating is used alongside current and voltage to establish the base efficiency, which indirectly affects the thermal heat loss calculation. Ensure the units (kW or hp) are correctly interpreted by the drive.
3. 99.13 Motor Connection: Verifying if the motor is wired in a Delta or Star (Wye) configuration is non-negotiable. An incorrect setting here will lead to a massive calculation error for the current-torque relationship, causing the drive to inaccurately estimate motor loading and resulting in premature or delayed I2t trips.

5.2. Practical Field Decision on Motor Power vs. Drive Rating

A common issue in plant upgrades is a slight mismatch between the motor power and the drive rating.

• Scenario: A $15 \text{ kW}$ motor is connected to an $18.5 \text{ kW}$ drive (a typical size increment).
• Technical Impact: The ACS880 drive, which uses the drive's nominal current as a starting point, will have excess capacity. If the motor data ($99.06$) is correctly entered, the thermal model will protect the motor accurately.
• Field Judgment: The engineer must confirm that the 99.06 Motor Nom Current value is strictly the $15 \text{ kW}$ motor's current, not the $18.5 \text{ kW}$ drive's current. Relying on the drive's default current value when a smaller motor is attached is a guarantee for eventual, critical thermal failure of the motor, as the I2t model would allow too much current for too long.

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6. Technical Specifications: ACS880 Thermal Model Characteristics

The following table provides a technical reference for the ACS880's thermal protection characteristics, guiding engineers in parameter adjustment. All data assumes motor nameplate data (Group 99) is correctly entered.

Protection Feature	Parameter Reference	Factory Default Setting	Technical Note for Field Use
Motor Thermal Protection Class	35.55 (Motor thermal time constant)	Varies, typically optimized for general purpose motors.	Directly determines the $I^2t$ trip curve sensitivity. Adjust from default only to match NEMA Class 20 ($700 s$) or Class 30 ($1050 s$) requirements for high-inertia or long-peak-load applications.
Motor Thermal Fault Limit	35.12 (Temperature 1 fault limit)	$100^\circ \text{C}$ (when using estimated temperature)	The percentage of thermal capacity at which Fault 5002 is triggered. Always leave this set to $100\%$. Do not bypass protection by increasing this value.
Motor Thermal Warning Limit	35.13 (Temperature 1 warning limit)	$80^\circ \text{C}$ (when using estimated temperature)	Sets the point where Warning A490 is generated. This is the engineer's first alert. A technician should investigate immediately if this warning appears repeatedly.
Cooling Method (Used for Model)	99.17 Cooling Type	Varies (Fan Cooled is typical)	Must match the physical motor. A misconfiguration (e.g., setting to self-cooled when it is actually fan-cooled) will miscalculate the zero-speed load limit and cause nuisance trips at low speeds.

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7. Final Reset and Validation Procedures

After a thorough mechanical inspection and parameter verification, the Fault 5002 can be reset. The engineer must then validate the system’s stability under load.

1. Reset: The fault can be reset via the control panel or parameter 16.02 Fault reset selection.
2. Start-up Monitoring: The motor should be restarted, preferably at a reduced load initially, while monitoring three key parameters simultaneously in the Drive Composer tool or the control panel’s Main Menu:
   • 01.01 Actual Current: Should be close to the rated current at full load, and not excessively fluctuating.
   • 35.15 Motor Temperature %: Observe the thermal utilization. It should stabilize well below the warning limit ($80\%$). If it quickly climbs back toward $80\%$, the root cause (mechanical load or severe parameter mismatch) is not yet fixed.
   • 01.07 Motor Speed: Verify the speed is stable and not oscillating, which can introduce current spikes.

Decision Point: If the 35.15 Motor Temperature % stabilizes below $70\%$ within five minutes of achieving steady state, the system is thermally stable. If it remains near $80\%$ or continues to climb, the original fault condition is still active, and the troubleshooting process must return to the mechanical inspection and advanced diagnostics (Section 4). The engineer's ultimate goal is to achieve reliable, continuous operation where the thermal utilization percentage offers a healthy margin to the warning and fault limits.

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Note to Readers: The technical content provided is for informational and educational purposes only and should not replace manufacturer documentation or professional field service. Always prioritize safety and consult official ABB manuals before attempting any repairs or parameter changes on live equipment.

The author assumes no liability for any loss, damage, or malfunction resulting from the use or application of this information. Use is strictly at the reader's own risk.