What to Do If a Motor Contactor Starter Fails to Hold On: A Practical Guide

When motors stop working as expected, the cause often traces back to the starter contactor. These devices handle the switching, protection, and control of electric motors, so even a small issue can bring operations to a halt. Knowing how to spot and fix problems quickly helps prevent downtime and costly repairs.

This guide looks at the most common motor starter contactor issues, explains their causes, and provides step-by-step troubleshooting tips.

Issue 1: Contactor Won’t Pull In / Fails to Hold On

When the contactor won’t pull in to start motor, or the motor contactor starter fails to hold on, the motor won’t energize at all. This is one of the most common starter faults.

Possible Causes

Before swapping parts, it helps to first understand what usually causes the issue.

• No control voltage present
• Faulty or open contactor coil
• Loose or broken wiring in the control circuit
• Auxiliary contacts not closing
• Undervoltage on the control supply

Troubleshooting Steps

Once you’ve identified the likely reasons, you can run through a few quick checks to confirm and correct the fault.

1. Measure the control voltage at the coil terminals. For example, if a 110vlt contactor won’t pull in to start motor, verify you’re getting the correct supply.
2. Test coil resistance with a multimeter. A faulty coil will read open circuit or very high resistance.
3. Check all control wiring for loose connections or breaks.
4. Inspect auxiliary contacts—if they are stuck open, the coil will not energize.
5. Confirm supply voltage is within tolerance; undervoltage can prevent the coil from staying engaged.

Issue 2: Motor Overload Tripping Frequently

If the starter keeps tripping, the motor can’t run for long without shutting down. This often points to either an actual overload or a protection device that isn’t set correctly.

Possible Causes

• Actual overload from heavy load on the motor
• Overload relay set too low
• Faulty overload relay
• Motor issues like bad bearings or winding problems
• Low voltage supply causing higher current draw

Troubleshooting Steps

After checking for these conditions, the next step is to measure and test systematically so you know if the issue is with the motor, the relay, or the power supply.

1. Check motor current with a clamp meter and match it against the nameplate value.
2. Reset the overload and watch if it trips under normal conditions.
3. Inspect the motor for mechanical drag or overheating.
4. Check that the supply voltage is steady and matches the required level.
5. If the relay is faulty, replace it with a trusted part like a TeSys LRD Thermal Relay.

Issue 3: Motor Starter Contactor Chatter / Humming

Hearing a motor starter contactor chatter or hum—sometimes called an electric motor starter contactor bouncing—is a clear sign something’s off. While the sound is annoying, it’s also a warning that the contactor isn’t holding properly.

Possible Causes

• Low or unstable control voltage
• Dirty or pitted pole faces
• Broken shading coil (on AC coils)
• Mechanical misalignment inside the contactor

Troubleshooting Steps

1. Measure and confirm the control voltage is steady.
2. Clean the pole faces to remove dirt or pitting.
3. Look over the shading coil; if it’s damaged, the contactor must be replaced.
4. If damage is extensive, install a new unit such as a Schneider TeSys Deca Contactor or LS MC Series AC Contactor.

Issue 4: Contacts Pitted or Welded

Alt-text: Mechanic using wrenches to repair industrial machinery components

Contacts are where the real work happens—carrying motor current and breaking the circuit during stops. Over time, they can become pitted or even welded together, which makes switching unreliable and unsafe.

Possible Causes

• Excessive arcing during operation
• Short circuits in the motor circuit
• Very frequent switching cycles
• Undersized contactor for the motor load

Troubleshooting Steps

If you see worn or damaged contacts, determine if repair is possible or if replacement is the safer choice.

1. Inspect contacts for burning, pitting, or welding.
2. Check the motor load against the contactor’s rating to avoid undersizing.
3. Reduce unnecessary switching where possible.
4. Replace badly worn contactors with robust models like TeSys Giga Contactors or ABB AX Line Contactors.

Safety First: Essential Precautions

Troubleshooting a motor starter contactor can expose you to dangerous voltages and moving parts. Safety must always come first, both to protect yourself and to prevent further damage to the system. Keep these precautions in mind every time you work on a starter:

• De-energize the circuit completely. Shut off power at the main source and apply lockout where possible. Don’t just rely on indicator lights—use a trusted tester to confirm that no voltage is present before touching any part of the system.
• Wear the right PPE. At minimum, this means insulated gloves, safety glasses, and flame-resistant clothing. In industrial plants, face shields or hearing protection may also be required.
• Follow wiring diagrams and labels. Starters often have multiple auxiliary circuits and interlocks. Consulting the correct diagram reduces the risk of reconnecting wires incorrectly or missing hidden faults.
• Beware of stored energy. Capacitors and spring-loaded mechanisms can still carry energy even after the system is switched off. Discharge capacitors safely and handle moving parts with caution.
• Work with proper tools. Use insulated screwdrivers, multimeters rated for the system’s voltage, and torque wrenches for tightening connections to manufacturer specs.
• Don’t work alone. If possible, have another qualified person nearby to assist in case of an accident.

By taking these steps, you protect yourself, reduce the chance of electrical accidents, and ensure that when the system is re-energized, it’s safe to run. Skipping safety steps may save minutes now but can lead to injuries, damaged equipment, and costly downtime later.

Finding Reliable Replacement Parts: The Simply Buy Advantage

When repairs require new components, quality matters. Cheap or counterfeit replacements may fail early, causing repeat breakdowns and safety risks.

Simply Buy Global offers a wide range of genuine contactors, overload relays, and protection devices from leading brands like Schneider Electric, ABB, Siemens, and LS. Their catalog includes:

• TeSys Deca Contactors – Compact, reliable choice for standard applications
• TeSys GV2 Motor Starter – Durable starters for pumps and HVAC systems
• TeSys Giga Protection Relays – Advanced safety for demanding industrial setups

With fast delivery, overseas warehouses, and flexible logistics, Simply Buy helps keep downtime to a minimum when you need parts the most.

What To Do if a Motor Contactor Starter Fails To Hold On: Conclusion

From when a contactor won’t pull in to start the motor, to when a motor contactor starter fails to hold on, or even when a motor starter contactor chatter becomes an issue, most problems trace back to a small set of causes. 

Following structured troubleshooting steps like the above and replacing worn parts with genuine components can keep your systems safe and reliable.

For expert support and access to trusted motor starter solutions, Simply Buy Global is here to help. Get in touch with us to find the right parts for your operation.