Contactor Troubleshooting Tips

The primary function of a contactor is to remotely switch electrical power. While relays and contactors do function similarly, contactors are designed to deal with higher amperages “in house” so to speak. In other words, a contactor deals with them in its switch mechanism.

These contactor troubleshooting tips will help you isolate and solve problems more quickly. Before you begin though — while this should go without saying, it should never be left unsaid — always de-energize a system, lock it out and tag it out before you perform any of the corrective procedures listed here.

How Contactors Work

Essentially a coil-actuated switch, the coil in a contactor is comprised of many winds that become energized with the application of low voltage. Movable solenoids are connected to contacts, which are usually a set of spring-loaded copper discs. The solenoids push against the springs to establish “contact” between the plates when energy is applied. When power is removed, the solenoids release and the springs decouple the contacts. Contactors can also have more than one set of contacts or switches.


Potential Issues & Solutions

Short Circuit – Typical causes include environments containing steam, dust, corrosive gasses or general dampness. Arc chutes can be damaged or fail. Positive and reverse contactors can be functioning improperly, or there could be unreliable interlocking, which could make both contactors pull in at the same time.

Possible Solutions — Improve the operating environment to eliminate unfavorable exposures. Examine and repair arc-extinguishing equipment. Investigate and correct the short load failure. Recheck the interlocking circuit to verify proper configuration for the operating mode.

Fusion Welding — This can result from short-circuiting on the load side, overload of the contacts, foreign conducting material between the contactors — or too little pressure from the contactor spring. Poor line contact leading to erratic operation can also induce fusion welding.

Possible Solutions — Separate the contacts with a screwdriver and clear the obstruction. Specify a higher capacity contactor, readjust spring pressure, check the coil control loop and reconnect it, or replace components as needed.

Overheated Contactor Coil — Excessive supply voltage, overuse, a high-temperature operating environment, a rough end face of the contactor’s iron core, or an iron core mechanical failure can cause this.

Possible Solutions — Measure and adjust the voltage, improve heat dissipation, clean and/or replace the iron core, look for flexibility in the contactor’s mechanical components, eliminate causes of damage and replace the coil.

Stuck or Restricted Iron Core — This can result from oil or dirt on the end surface, which impedes movement. Reaction springs can be damaged, the mechanical movement mechanism can also be damaged or rusty. Fusion welding (see problem above) can also be a culprit here.

Possible Solutions — Remove and clean the iron core, replace reaction springs, take the contactor apart and clear foreign debris, separate the contactors and file them smooth, eliminate the cause of the fusion welding.

Iron Core Won’t Suck Up — Power supply voltage can be too low, power loop or power supply isn’t connected, a defective contactor coil, a restricted contactor magnet or stuck contact, or there can be too much pressure on a contact from its spring.

Possible Solutions — Investigate the power supply and correct voltage anomalies. Examine the control loop and its connection. Replace damaged components. Measure coil resistance and replace it if too great. Look for a mechanical fault in the contactor, remove rusty components, add lubricating oil to the mechanism and replace damaged components. Measure and adjust contact spring pressure if needed.

These contactor troubleshooting tips will help you find and resolve the most commonly encountered problems. Again though always de-energize a system, lock it out and tag it out before you perform the corrective procedures listed here — and follow all other relevant safety guidelines for working with electrical equipment.




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