The Most Comprehensive Guidelines for installation and Maintenance of DC Contactor

As you already have an idea about the function and working of a DC contactor such as we know that a contactor is an electrically controlled switch used for switching electrical circuit. It is a unique type of relay but the main distinction between contactors and relays is the contactor’s ability to switch higher voltage and currents. Relay, on the other hand, is mostly used in lower current applications. Contactors are close-packed and can be installed easily in the field. They are mostly used in electric motors as motor contactors. Contactors come in a wide variety and have many different uses. Different contactors are designed for different environments and use. In this article, we will see how contactors are chosen and maintained in different conditions.

Choosing Right Type of  DC Contactors

In order to select the right type of contactor, you need to keep a few points in your mind, so you can get maximum efficiency. These include contactor coil type, main contacts, and auxiliary poles selection. For a contactor, such as 24 V DC contactors, we require a low power consumption option of the coil.  Furthermore, we need to consider the waveform of the control coil, power, and supply voltage fluctuations. Main contacts are based on the number of inductive and resistive load and we also need to determine how many main and auxiliary contacts are required. In order to ensure the proper working of a contactor, we need to fully regard the contactor load size, type, and polarity.

In addition to the above, we also need to consider the environment, temperature, and modular structure to select the right type of dc contactor. Moreover, we need to take into account the effect of actual temperature and coil voltage on operating, release, and bounce time. We also need to see, if the contactor needs to be enclosed, i.e. an enclosed motor starter required. Furthermore, we need to make sure if any ancillary parts are needed such as mechanical interlock, busbars, thermal overload relays, or circuit breakers.

Other than these, there are numerous other operational, climatic, and economic factors that need to be considered while buying the contactor set up. These include the type of load, durability, life span, and driving methods. Including this, we need to consider the type of control coil required and power voltage. In this article, we are going to discuss mostly DC contactors, but it should be understood that AC contactor is mostly used in switching such as transformer switching or condenser bank switching while DC contactors are used for dynamic suspensions.

Another important aspect to consider while selecting the right type of contactor is its price. Mostly, commercial use requires expensive contactors, while small scale market or home, requires relatively cheap contactors. Apart from this, the installation and maintenance price of contactors changes with different fields.

Climate for Storage and Functioning of contactors

The contactors have a variety of uses under many different circumstances, but they are made in strict optimal conditions. They need to store relative temperature and humidity, at an altitude of less than 2000m and should have no harmful and toxic gases in their immediate environment. If the device working is halted for some time, a heater should be used to maintain the temperature of the environment, this is because heat is not generated by the contactor itself that is required for the device. The different environment calls for the need of the various type of contactors that works best in that climate.

For example, in a rapidly changing climate, a magnetic switch causes rust activation fault by condensation. These contactors are mostly used in export in tropical areas where the climate is high. Similarly, in low temperatures such as in chillers and refrigerators, the magnetic switch is rusted away by moisture. In high temperatures, such as in an ironworks, the contactors have heat resistant connecting cable.

Magnetic contactors are not supposed to be used in high temperatures, so, if they’re to be utilized in these temperatures, it is advised to use by putting in an assembled type of humidity-proof structure, while considering insulation capacity, electrical durability, and rusting.  We need to consider protection treatment based on the environment. If the contactor is indoor and there is no condensation, the duty cycle is not important and internal heating is unnecessary. If there’s a risk of condensation, there should be frequent switching on and off for one whole day.

Apart from the risk of condensation and temperature, another thing we need to consider is the risk of dust and gas particles. In place of high dust level, the resistant structure should be a vibration-resistant structure. This is important because dust can degrade insulation capability and increase the risk of electricity short. When a magnetic contactor is used in chemical refineries, a protective structure is a must because of the risk of leakage of corrosive gas. It is advisable to blow clean air in the panel with help of an air conditioner.

Installation and Connections:

For safe use of DC contactors, be sure to read the instruction manual provided before starting to use it. There are a few safety instructions that you need to follow to ensure no harm. Many DC contactors are capable of arc extinguishing by using blow out the coil, which is turned on by load current. Thus, ensure your contactor is appropriate for the load current. Also, do not use DC contactors with an arc extinguishing chamber removed. To avoid breaking failure, be confident that there is no metal in arc space in overall dimension. While installing and routine maintenance checks, make sure to turn off all power switches to prevent accidents. Lastly, be sure to tighten up the mounting screws securely.

Before installing a DC contactor, make sure that the environment has no temperature and humidity anomaly and also that there are no harmful gases present in the environment. The atmosphere should be free from all poisonous gases, oil vapor, dust, and corrosive materials. The mounting surface should be completely flat so it is easier for maintenance. Process of installation includes the following steps:

  1. Selection of copper conductor for connection in accordance with capacity load.
  2. Ensure the provision of arc space as indicated in overall dimensions
  3. When providing the coil with some measure against the surge, make sure it does not slow down the contactor operation.
  4. When establishing a DC power supply, place the control on the DC side. Putting it on the AC side will decrease the contact opening speed

Now that we have discussed some basic principles of installation, we need to understand what type of connections we need to make for the installation of the contactor. The contactor should be installed at a specific angle with regular attachments following a vertical plane. However, the contactor can be skewed at 30° in any direction.

We need to set up rail fixtures and fastenings with the height ranging from 7.5 mm to 15 mm. Then, we need to ensure a specific distance between each contactor in order to acquire insulation distance. After this, we need to make screw tightening. First, we need to make sure that the voltage of the coil is the same as the voltage in the operating circuit. We have two types of terminal connections; y-type compression terminal and O-type connection terminal. We need to follow the connection assembly according to the manual guide to avoid any ambiguity.

Durability and Maintenance of Contacts

Magnetic contacts have limited endurance, due to stress under normal operating conditions. Stress is differentiated by the environment such as temperature, humidity, vibration, oil mist, and operational factors such as control voltage, on/off current, on/off frequency, installation, etc. For each stress factor, there is a heating action in the operating system which causes a certain heating effect. For example, if the relative temperature rises, the heating effect rises in coil temperature and that leads to a decrease in the coil life span.

For routine maintenance checks, we need to keep in mind several safety measures. First and most importantly, do not touch without checking the temperature of the unit. We should check the consumption condition because of switching durability. Be careful of inhaling toxic gases. In the end, tighten the set up in original settings.

At the contact point, we need inching, that is, breaking the driving current before the motor reaches driving speed by stopping the motor frequently. Plugging reverse torque when stopping the motor.

Now we need to understand when we will need a maintenance check. It is necessary when ruggedness occurs due to extreme switching, voltage fluctuation, or breaking large current. Another instance of maintenance is discoloration of connection due to sulfuration. The cause of sulfuration is hydrogen sulfide from polluted water. Another fact that leads to maintenance is chattering prevention. Chattering is caused by abnormal connection exhaustion. If this error is ignored, it can lead to phase short, which can result in severe injuries of workers present and, heavy economical losses.

      When these events happen, the electrical life of the contactor decreases, now we need to determine, whether to replace the product or not. We need to analyze abrasion on the contact point surface. We need to replace all 3 phases with new ones when the thickness of the point reaches under 50% of the new product.  To exchange the contact point, we need to remove the top cover and unscrew the top and bottom tightening terminal screws. If there are melting and fusion, we need to file up the contact point. But if the melting spreads, we need to replace the whole contactor.

If we were to use high heat resistant material, there will be no problem in isolation function. So, in this case, we only need to clean dust from abrasion. However, if there is a large rated capacity in the contactor, it needs to be removed because it is damaged by overuse.

To check for maintenance of the coil, do not touch the coil without checking the temperature first. To check the coil’s life span, check the coil color in routine. One important aspect of core and coil maintenance is the standard of the noise level. If we can hear noise 60cm away from the contactor, it is normal. Abnormal noise is caused by abnormal material from outside such as dust and oil mist. This can be prevented by ensuring the enclosure of an anti-corrosive and moisture-absorbent setup.

However, despite efficient casing, rusting can still happen in the core. Rust can be wiped by a dry towel or with sandpaper. If rusting is severe, we need to detach it by rubbing it with a wire brush.

There is a checklist that is provided by every contactor for daily maintenance. These include, the abnormal sound checking by hearing, abnormal smell, cover of the contactor, colour of the coil, loosening in assembly screw and endurance function aging.

Additional Auxiliary contacts and Other Accessories

In any setup, the magnetic switch can be installed with a variety of products according to the need and budget of the system.  These are used for circuit modification, processing improvement, and auxiliary accessories. These are panels that are attached to the front and sides of the contactor. It also includes a mechanical interlock kit for assembly of a number of contactors in a way that short circuit is avoided. Another interesting accessory in contactor setup is the surge load that is used to absorb the current surge in the coil during switching. We need to be extremely vigilant while connecting the surge absorber and keep it far from the product after use to avoid short circuits. Another newly emerging technology in this field is the reset device, which makes the panel door reset without operating the reset button of the relay. The reset bar needs to set up in a specific configuration, otherwise, it can cause extreme damage.


Magnetic contactors are used for remote use of motor starting, stopping, and protecting from motor burn out. As the operating current range is small so it cannot open a large current during a short circuit. Therefore, for maintenance of the product, we need to short circuit protection breaker recommended by International Electrotechnical Commission (IEC) standards. The protection functions include, disconnection function and short circuit protection molded case, control magnetic contactor that regulates on and off operation in the motor, heat and overload protection and load device with high protection range. There are protection conditions that should be considered when assessing cooperation in contactor working. Firstly, a magnetic switch should certainly be able to break current which can happen in normal operational conditions. Furthermore, the thickness of the circuit wire should be thick enough to not burn in electric shock. The current value of the intersection of operation should be less than the contactor’s breaking capacity. If these requirements are met, the cooperation is completed with maximum economic efficiency.

    When an electric breaker and a motor contactor are used together, in case of a short circuit the breaker will prevent most of the current to reach the switch(contactor) but even then some electrical contact will be transferred to the contactor so it should be made with most resistive material. Every contactor comes with a manual that shows which contactor can be used with which relay and motor rated power.

In general, there are two types of coordination, type 1 coordination in which the short circuit is not dangerous to humans or the installer and it is specified not to work with a part replacement. In type 2 coordination, the magnetic contactor is not dangerous to humans or the environment and is required to function, later on.

Keeping in mind all the discussion in this article, we can summarize the topic describing the important points regarding the inspection and maintenance of the contactor. Although the HOTSON’S contactors have a robust design, and they are durable, so they do not require repeated maintenance. However, to help maintain the equipment safety and minimal operational errors, the following things may be added to your preventive maintenance schedule.

Due to the frequent switching function of the contactor, it is important to pay attention to the described basic maintenance tips. Starting from the basic, use downtime for the cleaning of the connector. Regularly check the protection circuit of the contactor, replace it in case of any fault. Often check closures, in order to avoid loose connections. Regularly check the position of the stationary and moveable contact for the alignment.

Maintain the chamber arcing. Check it, if harmed or loosen, also check the change in position, avoiding the sundry metal granules in the arcing chamber slit. Regularly replace the invalidated contactor of any system. Note the type, power, coil, and voltage of the key parameters as you replace them to follow the system’s specification, and ensure the wiring is right and the contactor is fixed.

The resistance value for the interphase insulation should not be smaller than 10 Ohms. The motion of the auxiliary contacts is periodically tested to determine if the agility, touch stroke, can correspond to the special value.

 Following FAQ’S will further clear the points which are helpful for the maintenance of the DC contactor:

How to Perform a Basic Inspection on the DC Contactor?

Before the repair or maintenance process, make sure to obey the guidelines on all safety labels and instruction sheets supplied with the unit. One of the most critical aspects of a successful preventive maintenance program is inspection. Before it triggers downtime, a close examination of the contactor will typically reveal proof of a problem. Mostly you will save your time, if the concerns are corrected before they lead to significant breakdowns. The inspection consists of screening for symptoms of overheating, dust, loose components, abnormal noise, and all other signs of irregularities.

How to Maintain the DC contactor from Inside?

 It is necessary to keep the contactor clean for a successful operation, both inside and outside. Cleaning the contactor will help to prevent overheating, leakage of high voltage, and breakdowns. Clean with a blow of low-pressure dry air stream, making it dust and dirt free. Use the same method to remove the dust from the contact housing. Remove the magnet and the coil. To remove dust and dirt from the face of both the magnet and the armature, use a clean dry rag or a low-pressure dry air stream. Do not drop the magnet or scratch the pole faces of either the magnet or the armature. Handle them with care.

How to Check the Working of Solenoid Coil in a DC Contactor?

Maintenance of the solenoid coil is important. The insulation resistance of the coil must be measured. Regularly check the insulator for change in color and aging. Also, check the temperature of the coil. Keep in check the burning loss or open welding.

How to Maintain the Iron Core of the DC Contactor?

Keep in check the iron core maintenance. Always clean the surface area between the iron core and the moving parts.  Also, check the situation of the iron core whether it’s tight or not, it will cause operation noise if it is loose.

When Should the Contacts of a DC Contactor be Replaced?

Remove the cover of the arc and check the contacts. If there are any of the three conditions observed, you need to change the contacts. If there are unevenly worn silver cadmium tips, replace the contacts, or the tips are almost worn down on the contact’s copper content, or if the moveable contact of the copper material is discolored, you have to replace the contacts.

How to Avoid Discoloration of Wire Insulation?

It is natural the discoloration of the Silver Cadmium tips. But on all terminal connections, check for the proper torque. Wire and/or terminal discoloration can be a sign of a loose link. Brittle or discoloured wire insulation may also be a sign of a loose connection. The vibration will lead to loosen connections that can create complications eventually. Verify that the screws are secure when connecting the contactor to the panel.