Industrial motors rarely fail without a reason. When a motor won’t start, the problem is almost always tied to the control method, safety logic, or a missing command—not the motor itself. This guide walks through a practical, field‑tested troubleshooting approach used in industrial environments to quickly narrow down the cause.
Rather than guessing or replacing parts, this page helps you identify what symptoms to look for, what those symptoms mean, and where to focus your troubleshooting efforts based on how the motor is controlled.
- Start With the Control Method
- PLC-Controlled VFD Motor
- PLC Controlled VFD Troubleshooting Chart
- PLC-Controlled Motor Starter
- PLC Controlled Starter Troubleshooting Chart
- Relay Logic Motor Starter
- Switch Controlled Motor Starter Troubleshooting Chart
- A Logical Troubleshooting Order
Start With the Control Method
Before troubleshooting, identify whether the motor is controlled by a VFD, a PLC-driven motor starter, or relay logic.
PLC-Controlled VFD Motor
Problem: Drive Not Enabled
Symptoms
- VFD display shows “Disabled” or “Start Inhibited”
- No output frequency displayed
- Enable input status shows OFF even after command
- Motor does not attempt to start
Causes
- PLC output card not energizing the enable signal
- E-stop or safety circuit preventing enable
- VFD requires a secondary enable source that isn’t active
- Loose or broken enable wiring
Problem: Missing Run Command
Symptoms
- VFD powered and enabled but shows 0.00 Hz
- No “RUN” indicator active
- PLC rung for START appears true but output not energizing
- Operator presses Start but nothing happens
Causes
- PLC logic preventing run bit from setting
- Run command mapped to wrong VFD input
- HMI not sending run command
- Interlock conditions not satisfied (level/temp/pressure)
Problem: Faulted Drive
Symptoms
- VFD shows active fault code
- Fault light illuminated
- Motor may bump and immediately shut back down
- No response to Start command until cleared
Causes
- Overcurrent or overload condition
- Under/over-voltage on main input
- Motor short or ground fault
- Failed cooling fan causing overtemperature
- Refer to manual for fault summary and corrective actions
Problem: No Speed Reference
Symptoms
- VFD shows 0.00 Hz even with RUN active
- Analog reference input not updating
- Motor tries to run but remains at zero speed
- Potentiometer has no effect (if applicable)
Causes
- Broken or miswired 4–20mA or 0–10V signal
- PLC not writing frequency over communications
- Incorrect reference parameter selected
- Faulty potentiometer or analog input card
PLC Controlled VFD Troubleshooting Chart
PLC-Controlled Motor Starter
Problem: No Control Voltage
Symptoms
- No indicator lights on starter or panel
- Contactor does not pull in, even manually commanded
- PLC I/O appears normal but starter does nothing
Causes
- Blown control fuse
- Failed control transformer
- Open disconnect feeding control circuit
- Loose wire or broken terminal
Problem: Open Safety or Interlock
Symptoms
- Start button works but drops out immediately
- Safety relay refuses to reset
- PLC input tag shows “Not Safe” or “Interlock Open”
Causes
- Guard door open
- Tripped pressure/flow/temperature switch
- E-stop activated
- Safety relay fault or wiring failure
Problem: Starter Overload Tripped
Symptoms
- Overload reset button popped out / indicator lit
- Contactor pulls in briefly then drops
- Motor feels hot or jammed
Causes
- Motor drawing excessive current
- Incorrect overload heater size
- High ambient temperature
- Phase loss causing current imbalance
Problem: Failed Contactor Coil
Symptoms
- Contactor does not pull in even with voltage applied
- Coil may hum or get warm but not actuate
- Breaker trips when contacting failed coil
Causes
- Coil burned from overvoltage
- Wrong coil voltage installed
- Open winding from age
- Mechanical jam or welded contacts
PLC Controlled Starter Troubleshooting Chart
Relay Logic Motor Starter
Problem: Seal-In Circuit Not Made
Symptoms
- Motor starts only while holding Start button
- Contactor energizes then immediately drops
- No holding current seen on aux contact
Causes
- Aux contact not closing
- Wiring error in seal-in branch
- Start button signal too short
- Aux contact worn out
Problem: Stop Circuit Open
Symptoms
- System looks powered but Start does nothing
- PLC Stop input shows active/open
- No coil voltage present
Causes
- Stop button stuck
- Broken wire in series stop loop
- Tripped safety device
- Loose or corroded terminal
Problem: Failed Auxiliary Contact
Symptoms
- Contactor energizes but control logic never sees feedback
- PLC sees incorrect running status
- Seal-in fails even though contactor pulls in
Causes
- Worn or pitted contact face
- Internal mechanical failure
- Wrong NO/NC aux block installed
Problem: Control Transformer Issues
Symptoms
- No 24V/120V control voltage output
- Transformer hums loudly or overheats
- Fuses blow immediately on reset
Causes
- Blown primary or secondary fuse
- Incorrect tap setting
- Failed transformer winding
- Improper grounding
Switch Controlled Motor Starter Troubleshooting Chart
A Logical Troubleshooting Order
Problem: Power Issues
Symptoms
- No lights or indicators at all
- VFD or starter will not energize
Causes
- Blown fuses or breaker
- Phase loss
- Incorrect voltage
Problem: Control Signal Issues
Symptoms
- Start commands not reaching motor
- PLC output LEDs not activating
Causes
- Failed PLC output card
- Broken wire
Problem: Safety Circuit Issues
Symptoms
- Status shows “Safety Not OK”
- Start latches but immediately drops
Causes
- Open E-stop
- Open guard switch
- Faulty safety relay
Problem: Mechanical Issues
Symptoms
- Motor hums but does not rotate
- Shaft locked or jammed
- Burning smell or excessive vibration
Causes
- Seized bearings
- Locked pump or fan
- Broken coupling
Motors rarely fail without a reason. Follow the logic, and the root cause becomes clear.
Industrial Electrical Troubleshooting 
Leave a comment