Problems on this page:
Soft starter tripping during start
Hits OEE: Availability
Symptoms: The motor stops during the start ramp with an overload or current limit fault.
Current limit set too low for the load
Check the current limit and ramp time against the load the motor starts.
Load harder to start than usual
Check the driven machine for jams, cold oil or a full load at start.
Start ramp too long, overheating the starter
Check the ramp time and the number of starts per hour against the rating.
Supply voltage dipping at start
Check the supply voltage during the start.
Prevention: Start faults recorded with the starter fault code.
Soft starter overheating
Hits OEE: Availability
Symptoms: The starter trips on temperature or its heatsink is very hot.
Too many starts per hour
Check the start count against the starter rating.
Bypass contactor not closing after start
Check the bypass contactor and its control.
Cabinet ventilation poor
Check the cabinet fans and filters.
Starter undersized for the motor
Check the starter rating against the motor current.
Prevention: Cabinet temperature checked on a route.
Motor not starting
Hits OEE: Availability
Symptoms: The start command is given, but the motor does not turn.
Start signal not reaching the starter
Check the control wiring and the start signal.
Starter in a fault state
Read and reset the fault code after finding the cause.
Phase missing on the supply
Check all three phases at the starter input.
Motor or cable fault
Test the motor and cable insulation with them isolated; work on the starter only as an authorised person.
Prevention: Faults recorded per starter.
Water hammer on pump stops
Hits OEE: Availability
Symptoms: Pumps stop with a bang in the pipework.
Stop ramp not set
Use the soft stop or pump control setting of the starter.
Stop ramp too short
Lengthen the stop ramp.
Check valve slamming
Check the check valve type and condition.
Pump stopped by another device
Check that the stop goes through the starter, not a contactor upstream.
Prevention: Water hammer events recorded.
Nuisance phase or thyristor faults
Hits OEE: Availability
Symptoms: The starter reports phase imbalance or thyristor faults.
Supply phase imbalance
Measure the phase voltages.
Loose power connections
Check the power terminals with a thermal camera under load.
Thyristor failed
Have the starter tested and repaired by qualified staff.
Power factor capacitors on the motor side
Check that no capacitors are connected between the starter and the motor.
Prevention: Fault history reviewed monthly.
Settings lost or wrong after replacement
Hits OEE: Availability
Symptoms: A new or reset starter starts the motor badly.
Parameters not backed up
Record or save the parameters of every soft starter.
Motor current not entered
Set the motor full load current from the motor rating plate.
Ramp settings left at default
Set the start and stop ramps for the driven load.
Protection settings left at default
Check the overload class and protection settings for the motor.
Prevention: Parameter records kept per starter.
Motor running hot after starting
Hits OEE: Availability
Symptoms: The motor runs hot even though starts are smooth.
Bypass not closing, so current flows through the thyristors
Check that the bypass contactor closes at the end of the ramp.
Load above the motor rating
Measure the running current and compare it with the rating plate.
Supply voltage low or unbalanced
Measure the voltage on all three phases under load.
Motor cooling blocked
Clean the motor fan cover and cooling fins.
Prevention: Motor current trended.
Communication or remote control faults
Hits OEE: Availability
Symptoms: The starter does not respond to remote commands.
Fieldbus module fault
Check the communication module and its status lights.
Address or settings wrong
Check the network address and settings.
Local or remote mode wrong
Check the control mode setting.
Control power missing
Check the control supply to the starter.
Prevention: Communication faults logged.
Guidance only. Always follow lockout/tagout and your site's safe-work procedures, and verify against OEM manuals before acting.
Related equipment guides: VFD · electric motor · motor control centre · centrifugal pump · HMI panel
Stop the same fault coming back
Recurring soft starter stops usually trace to a cause you cannot see by hand. The partner we recommend is Fabrico: it tracks OEE and downtime live from PLCs, IoT sensors or AI cameras; where cameras are fitted, the video of a stop sits next to its machine data so the cause can be reviewed; and a technician opens the work order from the stop in the same system. Data is hosted in the AWS EU region, and Fabrico and the company behind it hold ISO/IEC 27001, ISO/IEC 20000-1 and ISO 9001.
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Related tools: full troubleshooting directory · OEE calculator · downtime cost · MTBF / MTTR · glossary
Methods that cut recurring stops: the six big losses · root cause analysis · preventive vs predictive maintenance · TPM · SMED & changeover