What Auxiliary Contacts Are? Why They Use And What Are The Benefits Of Auxiliary Contacts


Last Updated on November 27, 2022 by


It is common to use a variety of power protection devices in an electrical system. Among these devices, contacts, circuit breakers, and relays serve as the primary safety and protection devices. Protection equipment has multiple input and output points. This control allows circuit power to be precisely controlled. Apart from power control or power handling contacts, some contacts are available for devices that indicate the status of the electrical system to the central control system.

The types of contacts are called additional contacts. This article will elaborate detailed information about primary and auxiliary contacts. Therefore, we will discuss the primary and auxiliary contacts and their relationship.

The conventional mechanical contact inside the auxiliary circuit is known as the auxiliary contact. It is mechanically connected to the primary contacts and turns on simultaneously. It carries less current than usual. Additional names for auxiliary contact include control contact and additional contact.

Why are auxiliary contacts used in contactors?

Contactors are extraordinary power-controlling devices that are used in three-phase power systems. These power-controlling devices use an electromagnetic induction mechanism to open or close contacts of the contactor. Due to this electromagnetic mechanism, the controlling devices can be electrically insulated from the high-power main supply and load. Many contacts are available in the contactors, used for different purposes. For example, if a central power controlling unit is a PLC in an electrical system, and the load in this electrical system is a three-phase motor.

It is designed so that the PLC sends a signal to turn the motor through the contactor. Contactors are typically energized by their electromagnetic coils. This coil acts as an electromagnet and closes the normally open contacts in the contactor. This function is performed by the contactor’s central or “Power Contacts.” The motor will start running in regular operation if everything goes well, and smooth work will kick start. When the motor is unable to start following the closure of the primary contacts, there is a risk for damage to both the motor and the PLC.

Some extra contacts are used to avoid this in the contactors and power contacts. These additional contacts are called auxiliary contacts. The following section will learn about these auxiliary contacts in detail.

Auxiliary contacts

After knowing the purpose of auxiliary contacts, let’s explore the auxiliary contacts in more detail. These contacts are present on the contactors for the helping purpose. These are mainly feedback contacts, which monitor the overall activity of the whole electrical system. The auxiliary contacts start working when the electromagnetic coil energizes the primary contacts. These contacts check the status of each phase and load and give positive or negative signals back to the central controlling system like PLC. The fault cannot be detected automatically if there is no auxiliary contact in the system.

For example, auxiliary contacts monitor each phase’s voltages. When the voltage of any phase drops, the supply to the motor is disturbed, resulting in vibrations. If this situation persists for a long time, there are strong chances that motor winding could be heated up, and the motor could burn out.

An auxiliary contact on the contactor will also result in a low-phase situation. Then the auxiliary contact gives feedback to the PLC to immediately de-energize the magnetic coil to open the primary supply contact. The motor will directly go into the off state when the primary contact opens. As a result, auxiliary contacts save the motor from damage.

Benefits of auxiliary contact

Along with this feature, one can use auxiliary contact for several other purposes. Some of them are cited below.

Protection from electrical accidents

The auxiliary contacts provided extra safety features in an electrical system. The presence of auxiliary contact ensures the proper operation of the electrical system. These contacts indirectly turn off the power in case of any malfunction. If this power off did not happen, there are many more chances of overheating the system. And the danger of fire accidents increases significantly.

Avoiding electrical failure

Through auxiliary contacts, the risk of electrical failure is minimized. Because the overcurrent goes through the auxiliary contact, this will turn off the load by the controlling power system. This is a request the damage to equipment due to electrical failure could be avoided significantly.

Protection of power controlling devices like circuit breakers and contactors

Since the auxiliary contacts quickly switch off the main power by giving feedback to the central controlling circuits. Thus no excess current passes through the primary contacts of the contactors or circuit breakers. So, with “Auxiliary Contact,” the protection of power-controlling devices such as contactors and circuit breakers can be ensured.

Enhance the life of contactor, breaker, and relays

Heat is the main reason behind the damage to contactors, breakers, and relays. With the proper use of auxiliary contacts, you can protect the devices from excessive current and heat. Consequently, protection devices can last significantly longer after getting heat protection.

Time delaying capabilities

Some advanced auxiliary contacts have a particular function of time delay. This time delay feature avoids arcing while switching on or switching off the electrical circuits. This arcing also causes damage to the equipment. So, types of equipment can be safe from the arc of high current on and off time.


These are the details about auxiliary contacts. These contacts in your devices give you peace of mind that your equipment is secure. Always configure your contactor with the auxiliary contacts. These contacts give you an extra level of protection,

Frequently asked questions (FAQs)

Why do we need auxiliary contacts?

Alternatively, auxiliary contact is referred to as control contact or supplementary contact. It is an auxiliary function on a contactor, relay, or circuit breaker.

On what types of electrical devices can auxiliary contacts be mounted?

An electrical device can mount multiple auxiliary contacts. An example of a 3-pole contactor can be seen below, showing the main and auxiliary contacts. This contactor has three NO primary contacts, one NO auxiliary contact, and one NC auxiliary contact.