Motor Control Centre Troubleshooting: Causes & Fixes

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Problems on this page:

Starter tripping on overload Contactor chattering or not pulling in Hot spots in buckets or terminals Earth fault trips on a feeder Bucket will not rack in or out Indicator lights wrong Condensation inside the sections Drive in a bucket tripping

Starter tripping on overload

Hits OEE: Availability

Symptoms: A motor starter in the motor control centre trips its overload relay.

Motor really overloaded

Measure the motor current and check the driven machine for jams or drag.

Overload setting below the motor full load current

Set the overload to the motor nameplate current as the protection study sets.

Single phasing from a blown fuse or loose connection

Check all three phases at the starter and the motor.

Overload relay faulty

Test the relay and replace it if it trips early.

Prevention: Trips recorded per starter so repeat offenders stand out.

Contactor chattering or not pulling in

Hits OEE: Availability

Symptoms: A contactor buzzes, chatters or does not close, and the motor does not start.

Control voltage low

Measure the control transformer output under load.

Contactor coil failing

Replace the coil or contactor.

Dirt on the magnet faces

Clean the contactor with it isolated.

Loose control wiring

Tighten the control terminals.

Prevention: Control voltage checked during planned maintenance.

Hot spots in buckets or terminals

Hits OEE: Availability

Symptoms: A thermal survey shows hot terminals, stabs or bus connections.

Loose terminals

Retighten to the specified torque during an outage; work on the motor control centre is electrical work for authorised staff only.

Bucket stabs worn

Inspect and replace worn stabs.

Circuit loaded above its rating

Measure the load and correct it.

Poor ventilation in the room

Improve the room cooling.

Prevention: Thermal survey under load once a year.

Earth fault trips on a feeder

Hits OEE: Availability

Symptoms: An earth fault relay trips a motor feeder.

Motor winding insulation breaking down

Test the motor insulation resistance with it isolated.

Water in the motor terminal box

Dry the box and replace the gasket.

Cable damaged

Test the cable insulation.

Drive filter leakage

Check drives on the circuit.

Prevention: Insulation resistance of critical motors tested on a schedule.

Bucket will not rack in or out

Hits OEE: Availability

Symptoms: A withdrawable starter unit is stuck, or the interlock will not let it move.

Unit still switched on, so the interlock holds it

Switch the unit off before racking; the interlock is there to stop racking under load.

Racking mechanism dirty or dry

Clean the mechanism and lubricate it as the maker specifies.

Stabs misaligned with the vertical bus

Check the alignment of the unit and its stabs during an outage.

Guide rails bent or damaged

Repair or replace the rails.

Prevention: Withdrawable units racked out and in during planned maintenance.

Indicator lights wrong

Hits OEE: Quality

Symptoms: Run or trip lamps on the front of a unit disagree with what the starter is doing.

Lamp or LED failed

Replace it and use the lamp test to find others.

Auxiliary contact on the contactor faulty

Check the auxiliary contact block and replace it if it sticks.

Wiring changed from the drawings

Check the wiring against the current drawings and update them.

Indication supply fuse blown

Check the indication fuse and find what blew it.

Prevention: Lamp test run weekly.

Condensation inside the sections

Hits OEE: Availability

Symptoms: Moisture, rust or tracking marks appear inside the sections.

Anti-condensation heaters off or failed

Check the heaters and their thermostat.

Cable entries left open

Seal unused and open cable entries.

Room humidity high

Control the humidity and temperature of the switchroom.

Washdown water or steam reaching the room

Keep washdown away from the room and seal doors and openings.

Prevention: Heaters and seals checked before the cold season.

Drive in a bucket tripping

Hits OEE: Availability

Symptoms: A variable speed drive mounted in the motor control centre trips on fault.

Drive overheating in the enclosed section

Check the drive fans, filters and section ventilation.

Parameter changed

Compare the drive parameters with the saved backup.

Supply dips or harmonics

Record the supply to the section when the trips happen.

Motor cable or motor insulation fault

Test the motor cable and windings with them isolated.

Prevention: Drive fault codes logged and parameter backups kept current.

Guidance only. Always follow lockout/tagout and your site's safe-work procedures, and verify against OEM manuals before acting.

Related equipment guides: switchgear · transformer · VFD · electric motor · PLC · soft starter

Stop the same fault coming back

Recurring motor control centre 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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Methods that cut recurring stops: the six big losses · root cause analysis · preventive vs predictive maintenance · TPM · SMED & changeover