What is a contactor and how does it work?

Hello everyone! Welcome to Ausytoday.com! Have you ever come across the concept of a Contactor? For those of us who are involved in the world of electricity, we are probably used to encountering and experimenting with devices called contactors. However, those of us who are nonexperts or younger siblings currently enrolled in school might find ourselves pondering over the meaning and purpose of a contactor.

Definition of Contactor

A contactor is a crucial element in the control system, which operates to magnetically establish and sever the provision of electrical power to a three-phase electric burden.

One example of a contactor application is in the Direct On Line (DOL) electric motor starter circuit.

How does the Contactor work?

The contactor operates similarly to the light switches found in our households, albeit with some distinctions. While a light switch typically possesses just one set of terminals, the contactor boasts three pairs of terminals for both input and output.

Furthermore, conventional contactors typically include auxiliary contacts, namely Normally Open (NO) and Normally Close (NC) in pairs. The role of the NC auxiliary contact is to serve as an indicator for the off-state, while the NO auxiliary contact fulfils the role of an ON indicator and a holding circuit.

The purpose of the parable

The comparison between a contactor and a switch aims to simplify our comprehension of their operational principles. This is because, as ordinary individuals, we often find it simpler to grasp unfamiliar concepts when they are likened to familiar experiences that we encounter in our day-to-day existence.

Besides the variation in terminal quantity, the primary disparity between a contactor and a light switch lies in their modes of operation.

When we manually press the switch lever up and down, we are the ones controlling the light switch that moves the input and output contacts. In this process, the on-off processing contactor operates magnetically. It is activated by the magnetic field generated by the contactor winding, which carries current in coils A1 and A2. Specifically, coil A1 is connected to the source line, while A2 is connected to neutral (0). Alternatively, the connection arrangement could be reversed. Nonetheless, it is important to note that the contactor functions under the exact same working principle as a relay.

Furthermore, there exists a notable disparity between the contactor and the light switch in terms of the load they bear.

If we consider the load carried by the light switch, it typically consists of a conventional lamp, as its name suggests. However, on the other hand, the contactor handles a significantly more substantial load, such as three-phase electric motors, with a substantial power capacity.

Illustration image of standard switch and contactor

For the purpose of enhancing comprehension, let us ponder upon the visual representation provided below.

Above, you can observe an image depicting a light switch equipped with a single entry point (aptly coloured black) and a solitary exit point (glowing red/load line out).

Should the desire arise to establish a circuit that enables the state of the lamp to transition from ON to OFF, we may skillfully achieve this by seamlessly joining the originating line with the switch input, ultimately succeeding in linking the switch’s output with the illuminating apparatus. Meanwhile, the neutral component effortlessly commences its direct journey towards the designated area of the illuminating fittings.

Above is an ordinary contactor, showcasing 6 sets of junctions. Three sets are dedicated to the primary power pathway, while one set belongs to the normally open (NO) terminals. Additionally, we have the A1 and A2 coil terminals, which I elaborated on earlier, encompassing two pieces.

Let’s see if I can humanize the text for you:

Below, you will find a detailed description of the terminal located on the remarkable contactor device.

Primary input terminals: L1 (1), L2 (3), and L3 (5)
Primary output terminals: T1 (2), T2 (4), and T3 (6)
Additional terminals (Normally Open): 13 (input) and 14 (output)
Additional terminal (Normally Closed): 21 (input) and 22 (output)
Coil terminals: A1 and A2

Should you decide to utilize this contactor for the purpose of activating and deactivating a three-phase electric motor? all you need to do is establish a connection between a three-phase power source and the input terminals (L1, L2, and L3). Additionally, you will need to provide power to the electric motor by connecting it to the output terminals (T1, T2, and T3)

How to activate the contactor?

So, how can we activate it? Well, here’s where terminals A1 and A2 (coil/coil contactor) come into play. If we desire to initiate the motor, then we must provide a power source to the contactor coils A1 and A2. When the power supply is activated, a magnetic field will be generated on the coil, thereby automatically transitioning the terminal triggers from open to closed or from closed to open.

To put it simply, the connection is established between L1 and T1, L2 and T2, and L3 and T3 in order for the electrical current to flow from the source to the motor and power it up.

Now, how do we deactivate it? All that remains is to interrupt the current flow directed towards coils A1 and A2. Consequently, the contactor terminal will revert back to its initial position, effectively cutting off the power supply to the electric motor.

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