Spindle cables are one of the most critical, and most overlooked, parts of a CNC spindle system.
Many serious VFD faults are not caused by the spindle or the VFD itself. They are caused by cable damage that develops slowly over time, often hidden inside drag chains or cable sleeves.
This article explains why spindle cables fail, how to spot problems early, and when to stop and ask for help.
Why Spindle Cables Matter So Much
Spindle cables carry:
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High-frequency, high-current 3-phase power
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Fast voltage transitions generated by the VFD
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Sensitive ground and shielding paths
A single damaged conductor or compromised insulation can:
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Short a motor phase to ground
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Trigger hard VFD faults
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Cause intermittent errors that worsen under load
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Lead to permanent hardware damage if ignored
This is why cable-related faults often show up as:
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ERR17 (Motor-to-ground short)
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ERR38 (Output short circuit)
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ERR31 / ERR33 (Current detection faults)
How Drag Chains Damage Spindle Cables
Drag chains are useful, but they are also the number one cause of hidden cable damage.
Common failure causes include:
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Bend radius too tight
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Cable rubbing on chain links
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Repeated flexing at the same point
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No strain relief at entry or exit points
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Cable twisted inside the chain
Damage often occurs inside the insulation, where it cannot be seen until a fault appears.
If a fault only happens:
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Under load
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At certain machine positions
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After the machine has been running for a while
The cable is a prime suspect.
Strain Relief Best Practices
Proper strain relief dramatically extends cable life.
We strongly recommend:
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Strain relief at both the spindle end and VFD end
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No tension on connectors or gland fittings
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Gentle cable loops before entering drag chains
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Avoiding sharp bends immediately after connectors
Never allow the cable to support its own weight at the spindle.
Water-Cooled vs Air-Cooled Cable Risks
Water-Cooled Spindles
Additional risks include:
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Coolant leaks wicking into cable jackets
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Moisture intrusion at connectors
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Condensation in poorly sealed fittings
Even small leaks can:
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Compromise insulation
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Cause intermittent ground faults
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Trigger ERR17 or ERR38 under load
Air-Cooled Spindles
Primary risks are:
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Heat cycling
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Vibration
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Abrasion in drag chains
Both types require regular inspection.
Visual Inspection Checklist
Before resetting a fault or continuing operation, inspect the cable for:
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Cuts, nicks, or flattened areas
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Abrasion from drag chain links
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Coolant residue near connectors
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Loose or damaged strain reliefs
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Exposed shielding or conductors
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Burn marks or discoloration
If anything looks questionable, stop.
Running “just one more job” is how recoverable faults become permanent damage.
Grounding and Shielding: Why It Matters
Spindle cables include shielding to:
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Reduce electrical noise
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Protect sensitive electronics
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Provide a safe return path for interference
If shielding is compromised or grounding is poor:
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Noise increases
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Fault detection becomes unreliable
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Current may seek unintended paths
Shielding cannot protect you if the cable itself is damaged.
When to Stop and Contact Support
Stop and contact support if:
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ERR17 or ERR38 appears even once
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A fault repeats under load
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The cable has visible damage
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You suspect moisture intrusion
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You are unsure whether a cable is safe to reuse
Continuing to reset and run after these faults can cause irreversible damage.
We would rather help you inspect and replace a cable than see a VFD or spindle damaged.
Key Takeaway
Spindle cables are not passive accessories.
They are active, high-stress components.
Treat them with the same care as the spindle and VFD:
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Route them correctly
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Inspect them regularly
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Replace them at the first sign of damage
Doing so prevents most serious VFD faults before they ever happen.
