WAZIPOINT Engineering Science & Technology: Magnetic Contactor Connection Diagram

Tuesday, July 19, 2022

Magnetic Contactor Connection Diagram

Magnetic Contactor Connection Diagram
Magnetic Contactor Connection Diagram with a Three-Phase Motor

Magnetic Contactor Connection Diagram to Run a Motor in forwarding and Reverse Direction

Magnetic contactors are a form of electrical relay found on most electrically powered motors. They act as a go-between for direct power sources, and high-load electrical motors in order to homogenize or balance out changes in electrical frequency that may come from a power supply as well as to act as a safeguard.

A magnetic Contactor is an electromagnetically powered switching device, which functions much like a reel.

However, the relay is usually used at low power and voltage while the other hand, Magnetic contactor is used for high power.

It has an energized coil, iron core, several auxiliary contacts (NC, NO points), main contact terminals (3 contact points), and an overload relay.

It is usually used to start/stop or control large electric loads (electric motors) using a control circuit. It is used in motor control automation at the mill.

  1. It's easy and safe to control a large motor or large electrical load with a small push switch.
  2. It has a few auxiliary contacts (NC, NO points), indicating different signals or statuses.
  3. Because the TOLR is connected to it, it automatically stops the current load on the load when the current supply is over for any reason.
  4. In the case of a 3-phase motor, a 3-phase supply is provided, in which case a 4-phase supply can be easily provided using the Magnetic contactor.
  5. In the case of Star / Delta, it can be easily controlled using 1 Magnetic contactor.
  6. If the power supply is turned off, the current supply will be stopped at the load. This protects the device from the surge voltage.

Construction of Magnetic Contractors

A magnetic contactor has three parts. 1. power coil, 2.Auxiliary coil, 3.Spring mechanism. The power coil carries a high current and the auxiliary contactor receives a signal to make the contactor open or close or send the status of the contractor (on or off) to external systems like PLC, and SCDA. The spring mechanism provides mechanical force to make the contact on or off.

Enclosures are made of insulating materials like Bakelite, Nylon 6, and thermosetting plastics to protect and insulate the contacts and to provide some measure of protection against personnel touching the contacts.

These are Auxiliary contacts. Using these loads are created in the automation mode or the circuit of protection.

NC = Normally Close Normally, when its coil is not energized, its Auxiliary contract is closed.

NO = Normally Open Normal, that is, when its coil is not energized, its Auxiliary contract is open.

When its coil is energized (power supply), the NC point will be NO and the NO point becomes NC.

It has an Auxiliary block to connect to the Auxiliary.

How much voltage is activated with the magnet contactor's coil?

It comes in various ranges such as 24VDC, 24VAC, 110VAC, 240VAC, 415VAC
It is commonly referred to as a Magnetic Contactor. Usually, the terminals of the coil are marked by both A1 and A2.

Magnetic Contactor Types

The main categories in which the magnetic contactors are classified are the ac contactors and the dc contactors. 

There are a number of magnetic contactors which are used at every level with different appliances such as:

  1. Magnetic starter.
  2. Reversing starter.
  3. Star-Delta starter.
  4. Mercury contactor.
  5. Vacuum contactor.
  6. Mercury-wetted contactor.

Feature to Choose Magnetic Contractors
  1. The utilization category.
  2. Motor’s inrush current. AC1, AC3, kW/HP rating.
  3. The site electrical supply voltage.

Magnetic Contactor Connection Diagram for Motor to Forward and Reverse Direction
Magnetic Contactor Connection Diagram for Motor to forwarding and Reverse Direction

How Calculate the Sizing of Magnetic Contractor?

Consider these factors when sizing the magnetic contactor:

  • Load Type: AC-1 or Inductive ( AC-3 ) *Refer IEC rating table
  • Duty Cycle: One direction, reversing, plugging  * Refer to the manual instruction
  • Horse Power (hp)
  • Full Load Ampere ( FLA ) * Refer to the motor data plate information


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