| Under-voltage |
Under-voltage in the main circuit, check the electric level: Detected DC under-voltage value: Level S1 : 100V Level S2/T2 : 200V Level T4 : 350V |
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ERR08 – Under-Voltage Fault
What this means
ERR08 indicates that the VFD detected insufficient voltage on its internal DC bus. In simple terms, the VFD is not receiving enough stable power to safely run the spindle, especially under load.
This error commonly appears when the spindle begins cutting, even if it spins normally at idle.
Why This Happens
When the spindle is not cutting, power demand is low.
As soon as the tool plunges into material, current demand increases sharply.
If the incoming power:
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Drops momentarily
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Is already near the minimum acceptable level
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Is supplied through undersized wiring or shared circuits
the VFD will shut itself down to protect internal components.
Under-Voltage Thresholds
The VFD will trigger ERR08 when the DC bus voltage falls below:
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S1 systems (110V class): ~100V
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S2 / T2 systems (220V class): ~200V
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T4 systems (industrial): ~350V
Even short dips below these values can trigger the fault.
Most Common Causes We See
1. Power sag under load (most common)
Even if the spindle has its “own circuit,” voltage can still dip due to:
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Long wire runs
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Undersized wiring
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Weak breakers
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Shared upstream loads
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Older electrical panels
This often only shows up when cutting begins.
2. Extension cords or long cable runs
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Extension cords, especially 14-gauge or smaller, cause voltage drop
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Long runs from the breaker panel can do the same
Water-cooled spindles and VFDs are particularly sensitive to this.
3. Loose or poor electrical connections
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Loose terminals at the VFD
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Poor wall outlet contacts
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Worn receptacles
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Loose breaker connections
Any of these can cause brief voltage interruptions that trigger ERR08.
4. Supply voltage already near minimum
Some locations see naturally low line voltage, especially during peak usage hours.
What measures as “acceptable” at idle may not be sufficient under load.
What ERR08 Is Not
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Not a spindle defect
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Not caused by feeds and speeds alone
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Not a programming or tuning issue
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Not related to the motor itself in most cases
This is almost always a power delivery issue.
What to Check First
Step 1: Confirm dedicated power
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Ensure the VFD is on a dedicated circuit
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No dust collectors, heaters, compressors, or other large loads on the same branch
Step 2: Eliminate extension cords
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Plug the VFD directly into a wall outlet
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If unavoidable, use 12-gauge or heavier and keep it as short as possible
Step 3: Inspect all power connections
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Verify tight terminal screws at the VFD
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Check wall outlet fit and condition
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Inspect breaker seating
Step 4: Observe bus voltage (if available)
If your VFD displays DC bus voltage:
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Watch it during spindle startup and plunge
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If it drops sharply just before ERR08, that confirms under-voltage
Step 5: Try a lighter test cut
As a diagnostic step only:
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Reduce depth of cut
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Use a smaller tool
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Observe whether ERR08 still occurs
If lighter cuts run fine but normal cuts fail, power delivery is the issue.
Important Note for 110V Systems
110V VFD systems are far more sensitive to voltage drop than 220V systems.
This is normal behavior and not a defect.
If ERR08 persists despite good wiring and a dedicated circuit, upgrading to 220V power often resolves the issue entirely.
When to Contact Support
Reach out if:
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ERR08 happens immediately on startup
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Voltage is confirmed stable but fault persists
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You suspect internal VFD issues
When contacting support, include:
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Photos of the power wiring
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Circuit details
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Whether the fault occurs only under load
Summary
ERR08 means the VFD is protecting itself from low or unstable incoming power.
Most commonly caused by:
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Voltage drop under load
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Electrical supply limitations
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Wiring or connection issues
Once the power delivery is solid, this fault typically disappears completely.
