Contactor Failure, Causes and Maintenance (2022)

A contactor is a type of electrical control equipment that is used for switching on and off an electrical circuit. The function of a contactor is just like a relay, however, relays are used for lower current and are for protection purposes, while contactors are used to control higher currents electrical equipment. That is the reason that contactor is rated for thousand-ampere currents.

Table of Contents

Contactor parts and principle

Common parts of the contactor are Electromagnetic coil, Enclosure, and Contacts. The principle of operation of the contactor is simple. When current passes through the contactor, it energizes the coil or electromagnet. As a result, it produces a magnetic field. Which causes the armature core to move.

If it is Normally closed relay, the flow of current starts through the contacts. Now when the current supply disconnects, the coil de-energizes, and contact comes back to its original position.

Sometimes contactors fail to perform its function. There are different reasons behind this failure. In this article, I will study the causes of contactor failure and how to do maintenance.

(Video) Reasons of Contactor Failure | Contactor Troubleshooting

For more details about contactor, read my other article here.

Causes of contactor Failure

Different types of contactors are available in the market. Therefore, the uses may vary from one device to another. Similarly, there are different causes of contactor failure. Common causes are mentioned below.I will list them and then I will go in details:

Contactor failure causes list:

  • Overcurrent
  • Voltage fluctuation
  • Aging
  • Temperature rise
  • Poor installation
  • Product selection

Overcurrent

Passing an excessive current through contactor causes overheating. Which sometimes melts the contacts in the Normally closed position. So, when the contacts de-energize it is still closed position. And the contacts stick with each other, and of course the current still passing.

Therefore, it is mandatory to use specific rating contactors for a specific load. If the installed contactor is below the rated current. It will surely fail.

I have came through this fault several times in my work. It causes us serious issues. Some times a contactor is connected to control a heater through a thermostat, If the contacts melt and stick contacting together, the heater still working even if the thermostat disconnect the control voltage of the contactor.

Coil overcurrent

Coil overcurrent is another shape of overcurrent fault that can cause the burning of the electromagnetic coil. Which affects the overall performance of the contactor. This can happen if a short circuit inside the coil occur.

Voltage fluctuation

Variation in voltage is another cause of the failure of the contactor. Both types of fluctuations like over voltages and under voltages cause contactor failure.

(Video) What Causes a Contactor to Fail

As the operational limit of any contactor is between 85 Percent and 110 percent of the rated coil. So, in case of over-voltage speed of electromagnetic closing will increase. Over-voltage can also cause the burning of the electromagnetic coil.

Which affects the overall performance of the contactor. On the other hand, in the case of under voltages from the rated value, electromagnetic closing will decrease. Both cases cause a delay in the operation of a contactor, and hence the chances of contactor failure are more.

Aging

The aging of the contactors is another cause of contactor failure. With the passage of time, the efficiency of the contactor does not maintain at the same level due to the mechanical springs weakness, and contacts corrosion because of the spark during on and off operation.

Temperature rise

Another cause of contactor failure is the temperature rise. Sometimes contactors are placed in an area, where there is no proper ventilation of air. Hence it increases the temperature of the contactor. And reduce the efficiency while sometimes causing failure.

Poor Installation

Sometime contactors are installed at locations where there is a lot of vibration. Or it is a corrosive environment. Where vapors or chemicals can cause damage to contactor, and affect the efficiency of it.

In some dusty environments such as desert workplace, cement factories etc., the contactors suffer loosen connections, if installed in a poor IP rating panel. In such dusty environments the IP of the control panel should be suitable to provide protection for the contactor.

If the contactor has a loosen connection we simply use any kind of contact cleaner to clean it, or we can use an air jet to clean its contacts. But this process needs disconnecting power.

(Video) TOP 5 CONTACTOR Troubleshooting Problems!

Product selection

As mentioned earlier that each electrical device requires its own rated contactor. If contactor is installed at a wrong product, where the rated conditions of the contactor and product do not match. It will cause contactor to fail.

One of the important things to consider when rating a contactor for a load is the load type. Contactors have two types of current ratings, one for the thermal loads and the other is for other inductive loads.

I have written a detailed article about contactor thermal current, You can read it here.

electrical4uonline

Other misuse of electrical Terminologies

Different electrical terminologies like connection and mountings mistakes, Selection of wrong cable, Transients, change over time between star and delta connection, Voltage drops, and current peaks are common causes of contactor failure.

Contactor Maintenance

To ensure safe operation and prolong the life of contactor it is mandatory to carry out proper maintenance of contactor.

Maintenance of contactor involves different steps including an inspection. Therefore, before going for maintenance, it is mandatory to perform a visual inspection of the contactor.

  • In this type of inspection remove dust from the contactor.
  • Tighten the connections to prevent losing.
  • After this, it is time to check out the contact system of contactor.
  • Check whether the auxiliary contact is flexible. The static contact is loose or tight. Whether contact and stroke distance are according to the standards or not. If there is an issue with distance or contact. Address the issue before moving forward.
  • After all these now it’s time to check the electromagnetic coil. Address any issue if you find it abnormal in the coil or the overall core of contactor.

We are discussing some common maintenance steps of contactor in detail.

(Video) Why Contactor Coil Burn Out In Hindi | reason of contactor failure | troubleshooting

Contact System Maintenance

Contacts are important parts of contactor. The basic issue that comes in the contact system is inconsistency in a three-phase system, where all three phases do not close at a time.

If any of the contacts are affected, it causes disruption in operation. So always check for:

  • Whether the auxiliary contact is flexible.
  • The static contact is loose or tight.
  • Whether contact and stroke distance are according to the standards or not. If there is an issue with distance or contact.

Arc chute maintenance

Sometimes contactors sparks during operation, it is due to a piece of metal or cracks in the arc shroud. If you find any of it during inspection remove or repair/replace it immediately

Iron core maintenance

Iron core maintenance includes clearing the contactor core from any type of dust particle. In iron core maintenance check for the following

  • Whether short circuit ring is broken or detached?
  • Whether any noise comes from the core?
  • Whether there is any misalignment or electromagnetic coil suck well?

Electromagnetic coil maintenance

The electromagnetic coil can withstand 5% of tolerance in current or voltage. During this type of maintenance, check whether the coil heats up with voltage or current fluctuation.

Another factor is the quality of the coil if the coil is aged and does not perform well, replace it with a new one. Also, check any cracks or abnormal situations in the coil core. If it exists remove it at an earlier stage to get smooth operations.

FAQs

What happens if a contactor fails? ›

What Happens When The Contactor Is Faulty? When the contactor develops a fault or goes bad, it may need replacement. In such a case, it will not pull close. When that happens, the two ends do not connect with each other even when the current is directly run to it.

How can we prevent contactor failure? ›

(a) Ensure the cable is secure, the wire insulation is not damaged and refrain from having any loose ends. If the contact is loose, look out for any traces of burns. (b) Ensure strict measurement of the interphase insulation resistance of AC contactors, and the resistance value is not less than 10MΩ.

Why do contactors go bad? ›

Over time, contactors can burn out due to either normal wear and tear or overheating. When a contactor burns out, the component that it supplies electricity to will not be able to turn on. They can get stuck down.

How do you know if a contactor is faulty? ›

Bad AC Contactor Symptoms
  1. The condenser unit never shuts off. This could be a sign that the contactor has melted, leaving the air conditioner with no means to block electricity.
  2. AC hums and won't turn on. ...
  3. AC makes a chattering noise.

What causes a contactor to overheat? ›

Coils can overheat if operating voltages are too low or too high; if the contacts fail to open or close because of dirt or misalignment; or if they have suffered physical damage or experienced an electrical short.

Can contactors be repaired? ›

Contactor repair kits offer replacements parts or additional pieces for your device. Contactor repair kits offer replacements parts or additional pieces for your device.

What is the basic principle of contactor? ›

Operating Principle of a Contactor:The current passing through the contactor excites the electromagnet. The excited electromagnet produces a magnetic field, causing the contactor core to move the armature. A normally closed (NC) contact completes the circuit between the fixed contacts and the moving contacts.

What is the lifespan of a contactor? ›

For example, a properly applied contactor will have a life span of 10,000 to 100,000 operations when run under power; which is significantly less than the mechanical (non-powered) life of the same device which can be in excess of 20 million operations.

How do you test a contactor? ›

How to properly test a contactor - YouTube

When should a contactor be replaced? ›

Most manufacturers recommend that when the silver pad is one-half worn on AC contacts and on some silver-tipped DC ones, that the contacts be replaced. Electrical contacts withstand regular abuse from electric arcing - even when it's just a small jump. Even the largest contacts wear out after prolonged exposure.

Why is contactor tripping? ›

Contactors fail due to a wide range of reasons. Some of the common reasons are excess current flowing through the contacts. High current can be either due to overload or due to short-circuit. High current can cause the contacts to melt.

What happens when a contactor is overloaded? ›

If the current rises above a certain limit over a certain period of time, then the overload relay will trip, operating an auxiliary contact which interrupts the motor control circuit, de-energizing the contactor. This leads to the removal of the power to the motor.

What does T1 and T2 mean on a contactor? ›

Terminals T1 and T2 are a thermally activated contact on the resistor to indicate an overheat condition of the resistor. The contacts are normally closed and open once the braking resistor temperature reaches 120 degrees Centigrade. The minimum voltage/current for these contacts is 24VDC at .

What is A1 and A2 on a contactor? ›

A1 and A2 on a contactor typically refer to either end of the electromagnetic coil assembly. Most contactor manufacturers use A1 and A2 to designate the two terminals connecting electrical power to the contactor's magnetic coil.

How do you clean contactor? ›

AC Contactor Cleaning Product - YouTube

What is the common cause of problems with contactors? ›

The most common situation in contactor failures is contact sticking and coil burning. The reason for contact sticking; If more current is passed through the main power contacts than it can carry, the contacts will overheat after a while and the contacts may stick as a result of this warming.

What are the factors affecting life of contactor? ›

Electrical arcing is a key contributor to the shelf-life of a contactor. The arc between the contacts creates additional heat which is damaging the contact surfaces. Arcing is causing pitting,corrosion and oxide build up on contacts surface.

What are two basic types of contactors? ›

A DC contactor uses a magnetic quenching arc, while an AC contactor uses a grid arc as an extinguishing device.

What are the parts of a contactor? ›

A contactor consists of three basic parts: the operating coil, the associated magnetic circuit and the contacts that are actuated by the coil.

How often do contactors go bad? ›

Most contractors have an average lifespan of 5-10 years, depending on their usage, power source, and servicing. The life of the contactor is directly dependent on the main inrush current flowing through it, which should be Of AC-3 type load.

What causes contactors to weld? ›

QUESTION: What are the possible reasons for welding of contactor main contacts? ANSWER: • Speed of operation (sometimes called cycling) exceeding the specified values for the contactor. Issues in the contactor coil circuit • The contactor was exposed to a short-circuit. End of electrical life of the contactor.

What are the three types of overloads? ›

A few different types of overload relays include Bimetal Overloads, Ambient-Compensated Overload Relay, and Electronic Overload Relays.

What are the two types of overloads? ›

Overload Relay Types. These are classified into two types namely thermal overload relay and magnetic overload relay.

What is L1 L2 T1 T2 contactor? ›

2) Contacts terminals

The L1, L2, and L3 terminals are where the power wires connect to the contactor. The T1, T2, and T3 terminals are where the device wires connect to the contactor. The L1 contact connects to the T1 contact, the L2 contact connects to the T2 contact, and the L3 contact connects to the T3 contact.

What is 97 and 98 on a contactor? ›

Auxiliary contact

They are provided with two auxiliary contacts – one NO (97-98) and another NC (95-96). NO contact is for trip signaling and NC contact is for disconnecting the contactor.

What is T and L on contactor? ›

There are usually two contactors to each switch, marked as a line and terminal. The line (L) contains the voltage feed while the terminal (T) is connected to the electrical device being controlled.

What is R1 R2 R3 R4 contactor? ›

Terminals R1/R2 and R3/R4 indicate the normally closed power poles of this 4-pole contactor while terminals 1/2 and 3/4 indicate the normally open power poles.

What is 95 and 96 on a contactor? ›

The contact 95-96 is used to control the load contactor. The overload relays have a setting scale in Amperes, which allows the direct adjusting of the relay without any additional calculation.

How is contactor size calculated? ›

Size of Main Contactor = 100%X Full Load Current (Line). Size of Main Contactor =100%x6 = 6 Amp. Making/Breaking Capacity of Contactor= Value above Chart x Full Load Current (Line). Making/Breaking Capacity of Contactor=8×6= 52 Amp.

› white-paper › basics-of-con... ›

A contactor is a relay for switching an electrical circuit on or off. Most commonly used with electric motors and lighting applications, they provide a level of...
Contactors are heavy-duty electromagnetic switches that are normally used in controlling large lighting loads and motors. They operate similar to relays, bu...
Common coil voltages are 24V AC and DC coil, and 110V and 230V AC coil options, with many different amp and wattage levels within each individual category. An e...

What is the common cause of problems with contactors? ›

The most common situation in contactor failures is contact sticking and coil burning. The reason for contact sticking; If more current is passed through the main power contacts than it can carry, the contacts will overheat after a while and the contacts may stick as a result of this warming.

What tests do you need to take to check for a failed contactor? ›

Test the contractor: To test your AC contactor, first set your multimeter to the OL setting and then connect it to the low volt terminals. If the reading is between 5 and 20 volts, your contactor is working correctly. If you get a lower reading or no reading at all, your contactor is faulty and needs a replacement.

Can a contactor short out? ›

A shorted contactor has a resistance reading of zero. A small measurable resistance usually indicates a good coil. (If you have a good contactor measure it for your reference). The contacts must be in good enough condition to pass the voltage on to the load.

What is the lifespan of a contactor? ›

For example, a properly applied contactor will have a life span of 10,000 to 100,000 operations when run under power; which is significantly less than the mechanical (non-powered) life of the same device which can be in excess of 20 million operations.

Why is contactor tripping? ›

Contactors fail due to a wide range of reasons. Some of the common reasons are excess current flowing through the contacts. High current can be either due to overload or due to short-circuit. High current can cause the contacts to melt.

How do you test if a contactor is good? ›

How to properly test a contactor - YouTube

What causes a contactor to weld? ›

QUESTION: What are the possible reasons for welding of contactor main contacts? ANSWER: • Speed of operation (sometimes called cycling) exceeding the specified values for the contactor. Issues in the contactor coil circuit • The contactor was exposed to a short-circuit. End of electrical life of the contactor.

What does T1 and T2 mean on a contactor? ›

Terminals T1 and T2 are a thermally activated contact on the resistor to indicate an overheat condition of the resistor. The contacts are normally closed and open once the braking resistor temperature reaches 120 degrees Centigrade. The minimum voltage/current for these contacts is 24VDC at .

What is A1 and A2 on a contactor? ›

A1 and A2 on a contactor typically refer to either end of the electromagnetic coil assembly. Most contactor manufacturers use A1 and A2 to designate the two terminals connecting electrical power to the contactor's magnetic coil.

What does a bad contactor sound like? ›

Any kind of buzzing, humming or chattering noise emanating from a contactor indicates that you have a problem that needs investigation.

What happens when a contactor is overloaded? ›

If the current rises above a certain limit over a certain period of time, then the overload relay will trip, operating an auxiliary contact which interrupts the motor control circuit, de-energizing the contactor. This leads to the removal of the power to the motor.

Can a power surge damage a contactor? ›

Surge Damage

A surge could cause damage to multiple components and often includes the contactor and capacitor.

Can a contactor fail closed? ›

The overwhelming number of failure of motor contactors are failure to close. Welding happens but is often associated with fault currents and so is independent of contactor age or wear.

What is the main function of contactor? ›

A contactor is an electrical device which is used for switching an electrical circuit on or off. It is considered to be a special type of relay.

How often should a contactor be replaced? ›

A good contactor can last for almost ten or so years if it receives regular and annual maintenance. Sometimes, a contactor may simply have to be repaired. For smaller issues, a repair can do the trick.

› contactor-troublesho... ›


Contactor Troubleshooting Guide

https://www.obsoleteindustrial.com › contactor-troublesho...
https://www.obsoleteindustrial.com › contactor-troublesho...
A contactor is basically an electrically controlled switch. It is used to switch a separate power circuit, similar to a relay. The difference being that the iso...
Short circuit of the contactor. Possible causes of the fault: The contactor works in the environment of damp, dust, steam, or corrosive gases. The arc chute dam...

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