| External Fault | Fault caused by External Control Circuits |
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ERR13 – External Fault
What this means
ERR13 indicates that the VFD has received a fault signal from an external control circuit.
In simple terms, the VFD itself may be perfectly healthy, but something wired to its external fault or safety input has told it to stop.
This is a normal protective behavior when external safety or control logic is used.
Why This Happens
Many VFDs allow external devices to trigger a fault, such as:
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Emergency stop circuits
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Safety relays
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Interlock switches
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External control buttons
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CNC controller fault outputs
When the VFD sees this input change state, it immediately shuts down and reports ERR13.
Most Common Causes We See
1. External safety circuit opened (most common)
Examples:
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E-stop pressed
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Safety relay tripped
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Door or enclosure interlock opened
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MTC or external control circuit interrupted
This is expected behavior if a safety device is activated.
2. Loose or intermittent external wiring
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Loose terminal screw
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Wire pulled partially out
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Broken conductor
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Connector not fully seated
Intermittent wiring can cause ERR13 seemingly “out of nowhere”.
3. Incorrect wiring logic (NO vs NC)
If the VFD expects:
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Normally Closed (NC) wiring, but receives Normally Open (NO), or
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The logic is inverted relative to the controller
The VFD may immediately fault on startup.
4. Controller output misconfiguration
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CNC controller output assigned incorrectly
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Output disabled or inverted
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Firmware update changed output behavior
This is especially common after controller upgrades.
What to Check First
Step 1: Identify what is wired to the external fault input
Trace the wiring from the VFD’s external fault terminals and determine:
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What device is connected
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Whether it is a safety device, controller output, or manual switch
Step 2: Inspect wiring integrity
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Power down the VFD completely
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Check terminal tightness
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Look for damaged insulation or pulled wires
Step 3: Verify logic type
Confirm whether the VFD expects:
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Normally Closed (NC) or
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Normally Open (NO)
Ensure the connected device matches that expectation.
Step 4: Test by temporarily isolating the input
For diagnostic purposes only:
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Disconnect the external fault input
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Reset the VFD
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Verify whether ERR13 clears
If the fault disappears, the issue is confirmed to be external.
What ERR13 Is Not
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Not an internal VFD failure
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Not a motor or spindle issue
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Not caused by cutting load
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Not EMI related
ERR13 is almost always triggered intentionally or unintentionally by external wiring.
How to Clear ERR13
Once the external fault condition is resolved:
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Reset the VFD
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Ensure the external circuit is in its “safe” state
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Resume normal operation
The VFD will not restart until the external fault signal is cleared.
Summary
ERR13 means the VFD received a fault signal from an external device or circuit.
Most common causes:
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E-stop or safety circuit activation
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Loose external wiring
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Incorrect NO/NC wiring logic
Focus troubleshooting on external control wiring, not the spindle or VFD itself.
