| Motor Overheat | Detection on excessive temperature of the motor |
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ERR27 – Motor Overheat
What this means
ERR27 indicates that the spindle motor itself has overheated.
This fault is triggered when the VFD receives an over-temperature signal from the motor’s temperature sensor (or inferred thermal protection), indicating the motor is too hot to continue operating safely.
This is a protective shutdown to prevent permanent motor damage.
How This Is Different from ERR15
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ERR15 = VFD (drive) overheating
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ERR27 = Spindle motor overheating
These are separate systems with separate thermal protections.
Why This Happens
Spindle motors generate heat during operation. Under certain conditions, heat can build up faster than it can be dissipated.
When the motor temperature exceeds safe limits, ERR27 is triggered.
Most Common Causes We See
1. Sustained heavy cutting load (most common)
Examples:
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Aggressive depth of cut
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Large tooling on smaller spindles
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Extended cutting at high torque demand
Even if current limits are not exceeded, heat can accumulate over time.
2. Low RPM, high torque operation
Spindle cooling is less effective at low RPM.
Running:
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Heavy cuts
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Large tools
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Dense materials
At low RPM for extended periods can cause motor overheating.
3. Inadequate cooling
Depending on spindle type:
Water-cooled spindles
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Insufficient coolant flow
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Air trapped in coolant lines
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Pump failure
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Coolant temperature too high
Air-cooled spindles
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Blocked airflow
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Dust buildup
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Fan obstruction
4. Extended runtime without cooldown
Long jobs without pauses can:
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Gradually increase motor temperature
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Trigger ERR27 late into a job rather than immediately
5. Faulty temperature sensor or wiring (less common)
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Loose sensor wiring
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Damaged thermistor
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Connector issues
This can cause false overheat detection.
What to Check First
Step 1: Allow the spindle to cool
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Stop operation
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Allow sufficient cooldown time
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Do not reset and restart immediately
Restarting hot motors can cause repeated faults.
Step 2: Verify cooling system operation
For water-cooled spindles
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Confirm coolant is flowing
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Check for bubbles or air pockets
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Verify pump is running continuously
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Ensure coolant reservoir is not excessively warm
For air-cooled spindles
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Inspect air intakes and exhaust
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Remove dust buildup
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Verify fan operation
Step 3: Review cutting parameters
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Reduce depth of cut
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Reduce feed rate
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Increase RPM where tooling allows
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Break long jobs into segments
Step 4: Check sensor wiring
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Power down system
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Inspect temperature sensor connections
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Look for loose or damaged wires
What ERR27 Is Not
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Not a VFD overheating issue
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Not a communication or software fault
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Not EMI related
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Not a simple configuration error
ERR27 reflects a real thermal condition at the motor.
When to Contact Support
If:
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ERR27 occurs during light cutting
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Cooling is confirmed adequate
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The spindle overheats very quickly
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ERR27 appears immediately on startup
Support should evaluate:
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Temperature sensor integrity
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Motor health
Photos and coolant flow details are helpful.
Summary
ERR27 means the spindle motor temperature exceeded safe limits.
Most common causes:
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Sustained heavy cutting
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Low RPM, high torque use
-
Inadequate cooling
-
Long runtimes without cooldown
Ensure proper cooling and reasonable cutting parameters before resuming operation.
