How to Perform Motor Control Troubleshooting

The motor does the work. The motor control circuit decides when and how it runs.

From simple starters to complex reversing circuits, motor controls fail constantly in manufacturing environments. When a conveyor won’t start, or a hydraulic pump shuts down unexpectedly, the fault usually sits in the control logic, not the motor itself.

Your team needs motor control troubleshooting skills to restore automated systems fast. This is a core part of electrical maintenance training.

What Is Motor Control Troubleshooting?

Motor control troubleshooting is the process of isolating and repairing electrical faults in the circuits that govern industrial electric motors.

It covers two distinct circuit layers: the power circuit (high voltage to the motor) and the control circuit (lower voltage that operates contactors, relays, and timers).

Techs use schematics and multimeters to trace current through components like pushbuttons, limit switches, overload relays, and PLC outputs. The goal is to find the open circuit, short circuit, or mechanical failure that stops the motor from running its intended sequence.

Power Circuit vs Control Circuit

This is the most important distinction in motor control troubleshooting.

The power circuit runs from the main disconnect, through fuses or breakers, through the contactor contacts, through overload heaters, and into the motor.

The control circuit runs at a lower voltage (24VDC or 120VAC) and includes pilot devices like start buttons, sensors, and the contactor coil.

When a motor won’t start, ask one question first: Did the contactor coil pull in? If yes, and the motor still won’t run, the fault is in the power circuit. If the coil didn’t pull in, the fault is in the control circuit. That single test cuts your diagnostic time in half. For the broader systematic approach this fits into, see our guide on electrical troubleshooting for industrial equipment.

Read Ladder Diagrams

Ladder diagrams map out the logical sequence of a motor control circuit. Your techs need to read them fluently.

A tech troubleshoots a stuck conveyor by tracing the path from L1 to L2, checking every normally open (NO) and normally closed (NC) contact along the rung. If a safety interlock or limit switch sits stuck open, the schematic points directly to the failing field device.

Without schematic fluency, your team guesses. For the skills that support this, see our guide on electrical skills for maintenance technicians.

Diagnose Contactor Failures

Contactors take a physical beating. They snap open and closed thousands of times a week under electrical arc and mechanical stress.

Common failures:

• Pitted or welded contacts: Arcing during motor starts degrades copper contacts. Severe pitting causes a voltage imbalance. Welded contacts make the motor run continuously with no way to stop it.
• Coil failure: The electromagnetic coil burns out from overvoltage or mechanical binding of the armature. Test a coil with a multimeter on the resistance setting after LOTO. An infinite reading means the coil is open.
• Chattering: Loose connections or low control voltage make the contactor rapidly cycle open and close. That destroys contacts and the motor. For more on how contactor wear connects to broader electrical failures, see our guide on common electrical failures in industrial equipment.

Troubleshoot Overload Relays

Overload relays protect the motor from drawing too much current. When one trips, it opens the control circuit and shuts the contactor down.

Operators who reset overloads repeatedly to force production are masking a real problem. A trained tech measures the motor’s running current with an amp clamp, verifies the overload heater sizing, and inspects the driven equipment for a mechanical bind before resetting anything.

If the overload keeps tripping, the problem isn’t the overload. For more on diagnosing the motor side of this issue, see our guide on electric motor troubleshooting.

PLC-Integrated Motor Controls

Modern plants use PLCs as the primary pilot device. A PLC sends a 24VDC signal to a control relay, which pulls in the motor contactor.

Troubleshoot these hybrid systems in sequence: check the PLC output LED first, then verify voltage at the control relay, then confirm the contactor energizes. If the PLC output shows active but the relay doesn’t pull in, the fault is in the wiring between them. If the contactor energizes but the motor won’t run, move to the power circuit.

Recommended ITC Learning Courses

• Electrical Control Equipment: Covers contactors, overload relays, motor starters, VFDs, and control circuit troubleshooting.
• Programmable Logic Controllers: Teaches PLC operation, ladder logic, and I/O diagnostics for automation-integrated motor controls.
• Electrical Theory for Troubleshooters: Covers the foundational electrical theory behind power and control circuit behavior.
• Electrical Print Reading: Builds fluency in electrical schematics and ladder diagram interpretation.

Key Takeaways

• Separate the power circuit from the control circuit before you touch anything.
• Schematic reading is non-negotiable for fast, accurate motor control diagnosis.
• Contactors fail from pitted contacts, burned coils, and chattering caused by voltage drops.
• Overload trips need investigation, not just a reset.
• PLC-integrated motor systems need a sequential diagnostic approach across the output, relay, and contactor.

Want to speed up motor control fault diagnosis on your plant floor? Contact ITC Learning to explore motor control training for your maintenance team.

Frequently Asked Questions