Over-current at constant speed

The output current exceeds the over-current value while the frequency inverter is running at a constant speed.

Check whether the output circuit of the frequency inverter has a short circuit; Check whether the input voltage is relatively low; Check whether the load has mutation; Conduct parameter identification or improve low frequency torque compensation; Check whether the rated power of the motor or frequency inverter is large enough;

 

ERR01 – Over-Current at Constant Speed

What this means

ERR01 indicates that the VFD detected too much current while the spindle was already running at a steady speed. In simple terms, the spindle was asked to do more work than the motor or electrical system could safely support, so the VFD shut things down to protect the spindle.

This error happens after startup, once the spindle is already at RPM and cutting.

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Most Common Causes (Real-World)

1. Tooling load is too aggressive

This is by far the most common cause.

Examples:

• Large diameter tools on smaller spindles

• Too much depth of cut

• Feed rate too high for the tool and material

• Low RPM with a heavy chip load

A common example we see:

A 1.5 kW spindle being pushed with a 1/2” endmill at very high feed rates.

Even though the spindle is running, the cutting load spikes current beyond what the motor can supply continuously.

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2. Sudden load changes during cutting

• Entering material too aggressively

• Sharp corners or full-width engagement

• Toolpaths that don’t maintain consistent load

These can cause brief current spikes that trip ERR01.

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3. Low or unstable input voltage

If the incoming voltage drops while cutting:

• The spindle has to pull more current to maintain torque

• The VFD sees this as an over-current condition

This can happen even on “dedicated” circuits if:

• Wiring runs are long

• Outlets or terminals are loose

• The supply voltage is marginal

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4. Motor or VFD sizing mismatch

Less common, but possible:

• Motor is underpowered for the task

• VFD parameters do not match the motor correctly

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What to Do First (Recommended Order)

Step 1: Reduce cutting load

This usually solves the issue without touching any settings.

Try one or more of the following:

• Reduce depth of cut

• Reduce feed rate

• Increase RPM

• Use a smaller diameter tool

• Add ramping instead of straight plunges

Most users find that reducing depth of cut alone is enough.

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Step 2: Verify tooling and workholding

• Make sure the bit is sharp

• Check that the bit is properly seated and tightened

• Ensure material is securely held and not shifting

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Step 3: Check electrical supply

• Confirm the VFD is plugged directly into a solid outlet

• Avoid long extension cords

• Check that all power connections are tight

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Step 4: Advanced tuning (optional)

If ERR01 happens even under reasonable cutting conditions:

• Review low-frequency torque compensation

• Verify motor parameters match the spindle

• Confirm the VFD and motor are correctly sized for the application

Most users never need to go this far.

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Important Notes

• ERR01 is a protective fault, not a failure

• It does not mean the spindle is damaged

• Repeated ERR01 events are a sign the process needs adjustment, not that the hardware is bad

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Summary

ERR01 means the spindle is being overloaded while cutting.

In almost all cases:

• Reduce cutting load first

• Avoid pushing large tools too hard on smaller spindles

• Let the spindle work within its power envelope

If you continue to see ERR01 after reducing load, please contact support with details about the tool, RPM, feed rate, material, and depth of cut.