Never Do This: Unsafe Actions That Can Destroy a VFD or Spindle

This is one of the most important articles in our VFD knowledge base.

VFDs are powerful, intelligent devices designed to protect your spindle and electronics. However, there are a few actions that can instantly cause damage, trigger hard faults, or permanently destroy components.

Many of the most serious VFD failures we see are not defects. They are caused by unsafe actions that should never be performed.

If you take nothing else away from this article, take this:
Most catastrophic VFD failures are preventable.

❌ Never Unplug or Reconnect the Spindle While the VFD Is Powered

This is the fastest way to destroy a VFD.

Even if the spindle is not spinning:

The VFD still has energized output stages
Disconnecting the motor can cause voltage spikes
Reconnecting under power can short phases instantly

This commonly leads to:

ERR17 (Motor-to-ground short)
ERR38 (Output short circuit)
Driver board failure
Permanent VFD damage

Always power down the VFD and wait for the display to fully shut off before touching motor wiring.

❌ Never Swap Motor Phases While Powered or “Test” Directions This Way

Motor phase wires (U, V, W) must never be moved while the VFD is powered.

Swapping phases under power can:

Short output transistors
Confuse current detection circuits
Trigger hardware-level faults

This often results in:

ERR31 / ERR33 (Current detection faults)
ERR38 (Output short circuit)
Non-recoverable damage

If you need to reverse spindle rotation, do it in the VFD parameters, not by moving wires.

❌ Never Put Relays, Contactors, or Switches Between the VFD and the Motor

This is extremely important.

The motor must be wired directly to the VFD output.

Do NOT place:

Relays
Contactors
Emergency stop switches
Disconnects

Between the VFD and spindle motor.

Opening the motor circuit while the VFD is energized causes uncontrolled voltage spikes.

This leads to:

ERR35 (Motor switched while running)
ERR38 (Output short)
Destroyed output stages

If you need an E-Stop, it must cut input power to the VFD, not the motor output.

❌ Never Reuse a Damaged or Questionable Spindle Cable

Spindle cables live in harsh environments:

Drag chains
Vibration
Coolant exposure
Sharp bends

If insulation is compromised or shielding is damaged:

U, V, or W can short to ground
Shorts may only appear under load
Faults may appear “random”

This commonly causes:

ERR17 (Motor-to-ground short)
ERR38 (Output short circuit)
Intermittent faults that get worse over time

If a cable shows damage or has been pinched, replace it. Do not “try one more run.”

❌ Never Repeatedly Reset After a Short or Output Fault

If the VFD reports a short, overcurrent, or output fault, it is protecting itself.

Repeatedly resetting without fixing the cause can:

Overheat output transistors
Turn a recoverable fault into permanent damage
Mask the real issue until failure occurs

Common examples:

Resetting ERR17 without fixing a short
Resetting ERR38 while a cable is damaged
Resetting ERR31 or ERR33 without checking wiring

Stop. Power down. Inspect. Fix the cause first.

Why These Rules Exist

VFDs do not fail silently.
They fault loudly and early to prevent destruction.

Ignoring faults or bypassing protections removes that safety margin.

Almost every “dead VFD” case we see traces back to one of the items above.

Bottom Line

If you follow these rules:

Your VFD will protect your spindle
Errors will remain recoverable
Hardware damage is rare

If you break these rules:

Damage can happen instantly
Repairs are often not possible
Warranty coverage may be affected

When in doubt, power down and ask first.