Step-by-Step Troubleshooting Techniques to Diagnose a Faulty Contactor
Diagnosing a faulty electrical contactor doesn’t have to be overwhelming, even when time is of the essence. By following a structured approach and using the right tools, you can quickly identify and resolve issues, keeping your operations running smoothly.
Step 1: Addressing Inconsistent or Non-Operation
- Thermal Overload or Protective Devices: Confirm they haven’t tripped.
- Control Circuit: Use a voltmeter to verify the coil is receiving the correct voltage signal.
- Other Components: Consider potential issues with control relays, PLC outputs, or other components interrupting the signal to the contactor.
Step 2: Check Visual and Audible Signals
Begin with the basics—open the control panel and inspect the contactor for signs of damage. A worn-out or damaged contactor may have signs of smoke, soot, or discoloration that may suggest burning or overheating. A buzzing sound from AC contactors often points to a failing component. Typically, replacement is more cost effective than repair, as most small to medium-sized contactors aren’t designed for internal part replacement.
Step 3: Coil Testing
In order to check the signal to the contactor’s coil, the control cabinet needs to be powered on. Always observe all safety measures and utilize required protective gear where required whenever working inside a live electrical panel. All other tests should be conducted with the power disconnected. Using a voltmeter, make sure the correct signal voltage is being sent to the coil. If the required voltage is measured at the coil terminals, but the contactor isn’t actuating, test it using a multimeter set to measure resistance (ohms). Consult with the manufacturer’s product specifications for the resistance value of the coil. If the coil checks good and the contactor operates when the signal is applied, the coil is most likely not the problem, and the next check will be the contacts themselves.
Step 4: Measure Contact Resistance
Using an ohmmeter, place one probe on the line side terminal and the other probe on the load side terminal. Manually actuate the contactor and check the resistance across the contacts. It should read between 0 and a few tenths of an ohm. Repeat the test for all three contacts. Be sure to get a resistance reading of the probes themselves by touching them together first. Subtract this reading, if any, from the reading observed when checking the contacts.
If there’s no reading or the resistance is abnormally high, the contacts are likely faulty and the contactor needs replacement. Similarly, if there is resistance shown even when the contactor isn’t actuated, the contacts may be welded closed.
Step 5: Perform Preventative Maintenance
Regular maintenance can help avoid future issues:
- Thermal Imaging: Use a thermal imaging camera, if available, to detect overheating.
- Check Maintenance Records: Refer to any records for prior repairs or replacements.
- Manufacturer Recommendations: Follow the OEM's suggested intervals for replacing contactors based on usage patterns.
Quick Fix When You’re in a Pinch
While replacing a faulty contactor is always the best solution, you can attempt a temporary fix by disassembling the contactor and cleaning the contacts with a fine emery cloth. Keep in mind this is only a short-term solution, and the contactor should be replaced promptly—within a few weeks or even days.
Need More Help?
Still having trouble diagnosing your contactor? The team at All World is here to help! Reach out, and we can connect you with our experienced engineers who have been troubleshooting faulty contactors for decades. We’ll also assist in finding the right replacement contactor and even cross-reference your existing one with other brands.
Click here to contact us or browse All World’s inventory of in-stock parts, ready to ship the next day.
Keep your systems running smoothly—reach out to All World today!
