What is Auxiliary Contact and how it works with MCB? (2024)

A miniature circuit breaker can provide much more than current protection,it can also provide remote tripping, status indicator, under-voltage/overvoltage protection, and other features.

Auxiliary contacts (or switches) are supplementary contacts that are added to a circuit to protect the main contact. This accessory allows you to check the status of a Miniature Circuit Breaker or Supplementary Protector from a remote. Simply explained, it aids in remotely determining whether the breaker is open or closed. This device can be used for a variety of purposes other than remote status indication.

The Miniature Circuit Breaker will turn off the supply to the motor and protect it from the fault if the power circuit has a fault (short-circuit or overload). However, a closer examination of the control circuit reveals that the connections remain closed, supplying electricity to the contactor coil unnecessarily.

What is the function of the auxiliary contact?

When an overload triggers a MCB, the wire to the MCBmay burn. If this happens frequently, system may begin to smoke. Auxiliary contact are devices that allow one switch to control another (typically larger) switch.

The auxiliary contact has two sets of low current contacts on either end and a coil with high-power contacts inside. The group of contacts designated as “low voltage” is frequently identified.

Auxiliary contact, similar tomainpower contactor coils, which are rated for continuous duty throughout a plant, contain time delay elements that prevent arcing and possible damage if the auxiliary contact opens while the main contactor is still energized.

The main uses of Auxiliary contact are:

• Auxiliary contact is used to get the feedback of main contact whenever a trip occurs
• Auxiliary contactkeeps your circuit breakers and other equipmentprotected.
• Auxiliary contactprovides better protection against electrical damages.
• Auxiliary contactreduces the possibility of electrical failure.
• Auxiliary contact contributes to circuit breaker durability.

Difference between the main contact and the auxiliary contact:

Examples for Auxiliary Contacts

S 200 Auxiliary Contact in MCB:

• S 200 auxiliary contact- the toggle position of the MCB (On/Off) determines the switching position of the auxiliary contact.
• The auxiliary contact is utilized to indicate the condition of the MCB because it is connected to the switching mechanism.

S 800 Auxiliary Contact in MCB:

• Auxiliary and signal contacts are built within the MCB. The signal contact will indicate that the MCB has tripped in the case of an overload or short circuit.
• Because the signal contact is tied to the MCB’s trip mechanism, the signal contact will not provide an indication when the MCB is operated manually. The signal contact can also be reset without having to reset the MCB.

What is auxiliary contact in a contactor?

An auxiliary contact in a contactor is a secondary, low-current contact used for control and signaling purposes. Unlike the main contacts of a contactor, which switch the primary load (e.g., motors, lighting), auxiliary contacts are used to send signals to other devices, such as control circuits, indicating the status of the contactor (whether it is open or closed).Auxiliary contacts can be either normally open (NO) or normally closed (NC) and are often used for functions like interlocking, status indication, or triggering additional circuits in an automated system. They do not carry the main load but provide important feedback and control for the system’s operation.

How Does an Auxiliary Contactor Work?

An auxiliary contactor is a device used to control one switch by another, often to manage a larger or more powerful switch. It typically consists of a coil with high-power contacts, along with two sets of low current contacts. The low voltage contacts are often labeled for easy identification.

Unlike main power contactor coils, which are rated for continuous operation across an entire system, auxiliary contactors often include time delay features. These features prevent arcing or damage if the auxiliary contactor opens while the main contactor is still energized.

Why Use an Auxiliary Contactor?

Protection for Circuit Breakers and Equipment

• Auxiliary contactors protect circuit breakers and electrical equipment from overload damage. They release overloads before the main breaker or fuse is affected, reducing the strain on these components.
• By preventing current spikes and heat buildup, they help prolong the lifespan of circuit breakers and fuses, which might otherwise be compromised by under-capacity components.
• Many auxiliary contactors come equipped with their own fuses. In the event of a short circuit, the fuse in the auxiliary contactor will blow, protecting the main circuit breaker from damage.

Enhanced Electrical Safety

• Auxiliary contactors add an extra layer of protection against electrical hazards by ensuring that overloads are safely released. If an overload is not released in time, it can lead to circuit failure, overheating, or even fire hazards.
• These contactors help reduce the risk of electrical shocks and create a safer work environment by preventing dangerous malfunctions.

Minimizing Electrical Failure Risks

• By managing the load on circuit breakers, auxiliary contactors reduce the risk of electrical failures. Overloaded circuits can blow fuses, trip breakers, and cause overheating, all of which can damage equipment and create safety hazards.
• Auxiliary contactors trigger when overloads reach a certain threshold, allowing the electrical system to operate efficiently and prolonging the system’s life expectancy.

Auxiliary contactors offer critical protection and safety benefits in electrical systems, safeguarding against overloads, minimizing damage, and improving the overall reliability of the system

Some Frequently Asked Questions and Answers

What is the difference between load contact and auxiliary contact?

Load contacts are the primary contacts in a device, such as a contactor or circuit breaker, responsible for carrying the main current to the load (e.g., motors, lights). They handle higher currents and directly control the operation of the load.

Auxiliary contacts, on the other hand, are secondary contacts that operate in conjunction with the load contacts but handle lower currents. They are used for monitoring and signaling purposes, such as providing status feedback (ON/OFF), interlocking, or controlling additional circuits. Auxiliary contacts are not designed to handle the main power load.

What is the function of auxiliary contact in an MCB?

In a Miniature Circuit Breaker (MCB), the auxiliary contact is used for signaling and remote monitoring. It operates simultaneously with the main contacts of the MCB and provides information about the breaker’s status (whether it is open or closed). This can be useful for automation systems, allowing the MCB’s status to be monitored or triggering alarms when the MCB trips due to a fault.

Are auxiliary contacts normally open or closed?

Auxiliary contacts can be normally open (NO) or normally closed (NC), depending on their design and application.

• A normally open auxiliary contact remains open when the device (e.g., a circuit breaker or contactor) is in its default or inactive state, and it closes when the device is activated.
• A normally closed auxiliary contact, conversely, stays closed in the default state and opens when the device is activated.

The choice between NO and NC depends on whether you want the auxiliary circuit to be active when the main device is off or on.

What is auxiliary contact interlocking?

Auxiliary contact interlocking is a safety and control mechanism used to prevent two devices from operating simultaneously, which could lead to unsafe conditions or equipment damage. The auxiliary contacts of one device are used to control or block the operation of another device. For example, in electrical systems with two interlocked contactors, the auxiliary contact of one contactor can prevent the second contactor from being energized if the first is already active. This ensures coordinated and safe operation of multiple devices

Why Use an Auxiliary Contact in an AC Contactor?

An auxiliary contact in an AC contactor is used for several important reasons:

1. Status Monitoring: It provides feedback on whether the contactor is open or closed, allowing operators or control systems to monitor the contactor’s status remotely.
2. Control Circuit Integration: Auxiliary contacts are used to control additional circuits that depend on the contactor’s operation, such as alarms, indicator lights, or other control devices.
3. Interlocking and Safety: Auxiliary contacts can be part of an interlocking system to ensure safe and coordinated operation of multiple contactors, preventing unsafe conditions, such as two circuits being energized simultaneously.
4. Automation and Logic: They enable more complex automation tasks by allowing the control system to make decisions based on the state of the contactor, such as stopping one operation before starting another.

What are different types of contacts available in auxiliary contact?

Different types of contacts available in auxiliary contact are:

• Normally Open (NO) contact,
• Normally Closed (NC) contact,
• Change-Over (CO) contact.

MCB the changeover switch is a three-position switch with the middle position being the OFF position, the top position being connected to supply 1, and the bottom position being connected to supply 2. It serves as a switch between two power sources.