FANUC SP9029 Alarm 29: Short-Time Overload Troubleshooting

FANUC SP9029 means that an excessive spindle load remained above the configured overload level for the configured detection period. On applicable FANUC controls, the CNC shows SP9029 / SSPA:29 OVERLOAD, while the spindle amplifier displays 29.

In the standard setting described by FANUC, alarm 29 is generated when the load-meter reading remains at approximately 9 V for 30 seconds. These are standard values, not universal values for every machine. The actual detection level and time depend on the spindle system parameters and machine configuration.

For the surrounding alarm numbers, see the FANUC Serial Spindle Alarm Codes SP9001–SP9033.

What Does FANUC SP9029 Mean?

FANUC B-65285EN/04 defines amplifier alarm 29 as an excessive load applied continuously for a certain period. The word short-time refers to the motor or amplifier's short-duration load capability. It does not mean that the alarm is caused by one brief current spike.

The overload timer runs while the spindle load remains at or above the configured detection level. If the load drops below that level before the configured period expires, the condition may not produce alarm 29. If the high load continues, the spindle system stops and reports SP9029.

FANUC's procedure separates the fault by operating condition:

• Alarm during cutting

• Alarm while the spindle is stopped

• Alarm while the spindle turns only at very low speed instead of the commanded speed

• Alarm while the spindle does not rotate at all

This distinction is essential. A heavy cutting load, a mechanically locked spindle, an incorrect motor phase sequence and a failed spindle amplifier can all lead to alarm 29, but they require different checks.

Are 9 V and 30 Seconds Fixed Values?

No. B-65285EN/04 labels 9 V and 30 seconds as standard settings. In applicable αi/βi parameter configurations, B-65280EN/10 identifies:

• Parameter 4090 as the overload detection level

• Parameter 4123 as the short-time overload detection period

The cited parameter manual gives a typical initial overload level of 90% for αi spindle motors, 95% for βi spindle motors, and an initial detection period of 30 seconds. Parameter numbers, supported functions and initial values can vary with the CNC, spindle software and motor series.

Do not increase the overload level or extend the detection time simply to suppress SP9029. These settings protect the spindle system. Compare them with the exact motor parameter data, the original machine backup and the machine builder's specification. Any parameter correction must be followed by a controlled test without a workpiece before production resumes.

Main Causes of FANUC Alarm 29

The official alarm 29 procedure identifies the following diagnostic directions:

• Excessive cutting load. Aggressive depth of cut, feed, tool condition or another cutting condition keeps the load above the permitted level.

• Spindle mechanically locked during a low-speed or orientation command. The control continues to produce torque while an external mechanism prevents motion.

• Incorrect motor or sensor parameters. The spindle configuration does not match the installed motor and detector.

• Incorrect motor power-lead phase sequence. The motor cannot follow the commanded rotation correctly.

• Incorrect A/B feedback-signal connection. The detected rotation direction or speed feedback is inconsistent with the command.

• Faulty motor feedback cable or spindle sensor. The CNC or spindle check board does not indicate motor speed when the motor is turned manually.

• Abnormal motor power connection. The motor cannot receive the required output from the spindle amplifier.

• Incorrect spindle/output/winding-switching state. The required magnetic contactor is not on, or the parameters and PMC ladder do not match the installed switching system.

• Faulty spindle amplifier. FANUC lists replacement when the spindle does not rotate at all after the power-lead and switching checks are correct.

Alarm 29 is not proof that the spindle amplifier has failed. Record the alarm timing and eliminate load, mechanical, parameter, wiring, feedback and switching causes in the applicable branch before replacing the SPM.

1. Confirm SP9029 and Record the Operating Condition

Before changing parameters or disconnecting hardware, confirm:

• The CNC displays SP9029, SSPA:29 OVERLOAD or the series-specific equivalent.

• The spindle amplifier displays 29.

• The alarm is not SP9022, SP9031 or another overload-related number.

• The exact spindle command and load-meter value when the alarm occurs.

Record whether the alarm appears:

1. During a particular cutting operation

2. During spindle orientation or another stop-related command

3. When the spindle turns much slower than commanded

4. When the spindle does not rotate at all

5. During output, spindle or winding switching

Also record the complete CNC, spindle amplifier and motor models, including suffixes; the spindle software series; current motor and overload parameters; recent parameter or ladder changes; and any recent motor, sensor, amplifier or magnetic-contactor work.

Do not repeatedly reset the alarm and continue cutting. First remove the cause of the sustained load.

2. If SP9029 Occurs During Cutting

FANUC's first instruction for alarm 29 during cutting is to check the load meter and review the cutting condition.

Compare the alarm with:

• Spindle load during the same operation before the fault appeared

• Tool condition, runout and correct tool installation

• Depth and width of cut

• Feed rate and commanded spindle speed

• Workpiece material and stock allowance

• Coolant delivery and chip evacuation

• Any mechanical drag, abnormal noise or temperature rise

Reduce the cutting load using the approved machining process and repeat the operation cautiously. If the alarm disappears when the load is reduced, investigate why the original process exceeded the available spindle output instead of adjusting the protection parameters.

If the load is unexpectedly high even with the tool clear of the workpiece, stop treating the event as a cutting-only issue. Check for spindle mechanical resistance, an unintended lock, switching problems or abnormal commanded motion.

3. If SP9029 Occurs While the Spindle Is Stopped

Alarm 29 can be issued while the spindle appears stopped if the control is commanding orientation or very slow motion while the spindle is mechanically locked.

Check whether:

• A spindle orientation command remains active

• A very-low-speed command is being issued

• A spindle brake, clamp, gearbox or external locking mechanism remains engaged

• The PMC ladder releases the mechanical lock before torque is commanded

• The completion and interlock signals change in the correct sequence

The key issue is not simply that the spindle is stationary. It is that the amplifier continues to produce current because the commanded motion cannot occur. Correct the mechanical or sequence interlock before retesting.

Do not bypass a spindle brake or safety interlock merely to clear the alarm. Verify the intended sequence in the machine builder's electrical and ladder documentation.

4. If the Spindle Rotates Only at Very Low Speed

When the spindle does not follow the command and rotates only at very low speed, FANUC directs the technician to check parameters, phase sequence and motor feedback.

Verify the motor and sensor parameters

Identify the exact spindle motor and detector configuration. Compare the current spindle parameters with the applicable B-65280EN parameter manual, the original machine backup and the machine builder's data. Initialization should be performed only when the correct motor data and approved procedure are available. Do not initialize parameters as a trial-and-error step.

Verify the motor power phase sequence

Check that the spindle amplifier-to-motor power leads are connected in the specified phase order. This work involves hazardous voltage and must be performed with power isolated by trained personnel.

Verify the A/B feedback signals and cable

Check that the motor feedback A/B signals are connected correctly. FANUC also instructs technicians to turn the motor manually and observe whether motor speed appears on the CNC diagnosis screen or spindle check board.

If no speed is displayed, test the feedback path and replace the faulty feedback cable or spindle sensor/motor identified by the applicable procedure. Do not confuse this motor-feedback check with the αi position-coder cable used in SP9027 diagnosis; confirm the actual sensor and connector from the machine drawing.

5. If the Spindle Does Not Rotate at All

When the spindle receives a command but does not rotate at all, check the motor power path first:

• Correct connection between the spindle amplifier and motor

• Loose, open, damaged or incorrectly landed power leads

• Correct magnetic-contactor operation where spindle switching, output switching or winding switching is used

• Required auxiliary-contact and state-confirmation signals

• Mechanical locks and interlocks that could prevent rotation

If a dual-winding motor or switched output is installed, confirm that the parameters match the hardware and that the PMC ladder commands the correct contactor in the correct sequence. The switching checks do not apply to a machine without this configuration.

Never energize conflicting winding or output contactors to test the circuit. Incorrect switching can damage the motor, contactors or spindle amplifier.

If the motor power connection and applicable switching circuit are correct but the spindle still does not rotate and alarm 29 remains, FANUC lists the spindle amplifier as the next hardware direction.

When Should the Spindle Amplifier Be Replaced?

FANUC does not specify immediate SPM replacement for every SP9029 case. Replacement is listed in the no-rotation branch after the motor power lead and applicable switching contactor have been checked.

Before replacing the amplifier, verify:

• The alarm occurs without an excessive cutting command or mechanical lock

• Motor and sensor parameters match the installed equipment

• Motor power phase sequence and feedback signals are correct

• The motor power cable and feedback cable have been tested

• Switching contactors, wiring and ladder sequence are correct where used

• The exact amplifier model, suffix and spindle software compatibility are known

If amplifier replacement is required, browse FANUC servo, spindle and power drives or send REACO CNC the complete amplifier number for a compatibility check.

Replacement and live electrical testing must be performed by qualified personnel. Isolate machine power and observe the DC-link discharge time stated in the applicable FANUC and machine builder manuals.

Difference Between SP9029, SP9022 and SP9031

These alarms can share causes such as excessive load, a locked spindle or incorrect wiring, but they are not interchangeable. Always use the exact number on the spindle amplifier and follow the procedure for that number.

FANUC SP9029 Diagnostic Table

Recommended Troubleshooting Order

1. Confirm SP9029 on the CNC and alarm 29 on the spindle amplifier.

2. Record the load-meter value, spindle command and exact condition in which the alarm appears.

3. If it occurs during cutting, inspect the tool and process, then reduce the cutting load.

4. If it occurs while stopped or during orientation, check for a mechanical lock and verify the PMC release sequence.

5. If the spindle turns only at very low speed, verify motor/sensor parameters, power phase sequence, A/B feedback signals and speed indication.

6. If the spindle does not rotate, inspect the motor power connection and applicable switching contactors.

7. For dual-winding or switched-output systems only, verify the motor parameters, contactor state and ladder switching logic.

8. Test the motor feedback cable and sensor/motor when the diagnosis screen or check board shows no speed.

9. Evaluate or replace the exact compatible spindle amplifier only after the external causes in the applicable branch have been eliminated.

10. Retest without a workpiece using the machine builder's approved procedure, then confirm the load under normal operation.

Technical References

• FANUC AC Servo Motor αis/αi Series, AC Spindle Motor αi Series, Servo Amplifier αi Series Maintenance Manual, B-65285EN/04, Alarm Code 29

• FANUC Series 0i-D/0i Mate-D Maintenance Manual, B-64305EN/03, SP9029 alarm list

• FANUC AC Spindle Motor αi/βi Series Parameter Manual, B-65280EN/10, overload detection level and short-time overload detection period

• FANUC Servo Amplifier αi Series Descriptions, B-65282EN, motor power wiring and switching connections

• Beijing FANUC SP9029 technical guidance, short-time overload troubleshooting

Always use the manual edition, parameter data and electrical drawing that apply to the exact CNC, spindle amplifier, motor, detector, spindle software and machine configuration.

Need Help With FANUC SP9029 Alarm?

REACO CNC provides independent FANUC spindle load diagnosis, spindle amplifier testing, repair, parameter checking and replacement support. Send us the CNC alarm screen, amplifier display, complete CNC model, exact spindle amplifier and motor models with suffixes, load-meter value, alarm timing, and details of any recent parameter, ladder, wiring or switching work.

Visit the FANUC Technical Support Center for more FANUC alarm guides, or contact REACO CNC for assistance.

Reference Source: Beijing FANUC. This article is based on FANUC technical documentation. The applicable load, parameter, feedback, switching and amplifier procedure depends on the exact CNC, spindle system and machine configuration.