| Output short circuit | 3-phase output inter-phase short circuit |
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ERR38 – Output Short Circuit (Inter-Phase Short)
What this means
ERR38 indicates that the VFD has detected a short circuit between two or more motor output phases (U, V, W).
In simple terms:
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Two motor phases are electrically touching
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This creates a dangerous condition
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The VFD shuts down immediately to protect itself and the motor
This is a serious electrical fault.
Why This Is Dangerous
A phase-to-phase short can:
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Instantly damage output transistors
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Destroy driver boards
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Permanently damage the VFD
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Damage the spindle motor windings
ERR38 exists to prevent catastrophic failure.
Most Common Causes
1. Damaged spindle cable
The most common cause.
Examples:
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Crushed cable in drag chain
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Pinched cable at strain relief
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Abrasion through insulation
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Melted insulation from overheating
If two phase conductors touch, ERR38 will trigger.
2. Faulty or damaged motor connector
Common issues:
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Bent pins in aviation connectors
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Loose or twisted pins
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Improperly terminated connectors
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Moisture intrusion causing internal shorts
3. Internal spindle motor fault
Less common, but possible:
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Internal winding insulation failure
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Overheating damage
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Coolant ingress in water-cooled spindles
4. Incorrect wiring or modification
ERR38 may occur after:
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Rewiring the spindle
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Connector replacement
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Custom cable modifications
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Incorrect pinouts
What to Do Immediately
⚠️ STOP OPERATING THE VFD ⚠️
Do not reset and retry repeatedly.
Repeated attempts can permanently damage the VFD.
What to Check First
Step 1: Power down completely
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Turn off the VFD
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Disconnect input power
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Wait at least 3 minutes for discharge
Step 2: Inspect the spindle cable
Carefully inspect the entire cable length for:
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Cuts
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Flattened sections
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Burn marks
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Exposed conductors
Pay close attention to:
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Drag chain entry points
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Connector strain reliefs
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Areas near motion joints
Step 3: Inspect connectors
Check:
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Aviation connector pins
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No bent or touching pins
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No debris or moisture
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Proper pin alignment
Step 4: Test motor isolation (if equipped)
If you have a multimeter:
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Check continuity between U-V, V-W, U-W
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There should be no continuity between phases
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There should be no continuity to ground
If continuity exists, a short is present.
What Will Not Fix ERR38
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Power cycling alone
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Changing feeds or speeds
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Adjusting acceleration
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Re-running motor identification
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Resetting alarms repeatedly
ERR38 will return until the short is eliminated.
When to Contact Support
If:
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Cable damage is suspected
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Connector damage is found
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The spindle itself may be faulty
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ERR38 persists after cable inspection
Contact support before powering the VFD again.
Provide:
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Photos of the cable and connectors
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VFD model
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Spindle model
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Any recent events (crash, coolant leak, cable pinch)
Summary
ERR38 means a phase-to-phase short circuit exists between motor outputs.
Most common causes:
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Damaged spindle cable
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Faulty connectors
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Internal motor failure
This is a critical electrical fault and must be resolved before further operation.
