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Direct Online Starter / DOL Starter Wiring Diagram

For induction motor controlling we use different methods and starter wiring connections in which the most used method and diagram is dol starter wiring diagram (direct online starter). This method consist a circuit breaker (MCCB), magnetic contactor , thermal or electronic overload relay and push button switches for one off. This method we use for 3 phase induction motor, however we can also use the DOL for Single phase induction motor but when we talk about the controlling  a single phase induction motor then electronic or CT (current transformer) type relay will be consider better then using of thermal overload relay.

DOL Direct Online Starter Explanation

As i told that this circuit consist MCCB , MC, and overload relay. So first we lighting about the all part devices which we use in DOL.

MCCB which mean molded case circuit breaker, we use this circuit as main circuit breaker. From which we control the incoming supply. So if you did not know.  about how can you control the three phase supply using MCCB then the flowing post will help you in understanding.

How to wire 3 and 4 pole MCCB Breaker?
What’s Magnetic Contactor and How it’s works?

Magnetic contact or is the second part of this circuit. A magnetic cont actor have two types of contact which we know with name of main contacts and auxiliary contacts. And A1 and A2 for coil. The main contacts is normally open and when the cont actor operate these contacts make a close circuit between one anther. The input points for these contacts is T1, T2 and T3 or the L1 , L2 and L3. And the out points denote with U V W.

Overload relay
There are two types for overload relay which are thermal overload relay and electronic overload relay, in the below diagram is shown the thermal overload relay connection.

Push button switches.
We use two push bottom switches for direct online stater, in which one is normally open contacts and 2nd is normally close contacts, The NC contacts button we used for switch off the motor and NO is for switch On.

Direct Online Starter – DOL Starter Wiring Diagram

Here is the complete dol starter wiring diagram from which you learn these connection easily.

dol starter wiring diagram
Direct online starter diagram

In the above diagram DOL stater wiring diagram, i shown a 3 pole MCCB circuit breaker and after that i shown the Magnetic condactor and then a thermal overload relay. I also shown the normally close and normally open switch. The upper circuit breaker free terminals or connection points is for input and bottom thermals overload relay free contacts is for load or 3 phase motor. However lets do it step by step

  • First of all do the main connection between the circuit breaker and magnetic contactor as i shown with the red yellow and blue color line between the breaker and starter.
  • Then do connection between the contactor and overload relay as i shown in the above dol starter wiring diagram.
  • In the above diagram i shown cont actor which coil is operate on 380 to 440 volts, so we don’t need neutral. I get a wire connection form red wire form place of mccb breaker output point and connect to contact or coil. You can see it in the above diagram and i use a thin red line for that connection.
  • After that i get the connection from blue wire and connect the wire to thermal overload normally close contacts one side and get connection for switch form other contact. i.e example if the thermal overload relay normally close contacts is 95 – 96 , so i connect the wire to 95 and get it form 96 and connect this wire to the normally close push bottom switch which is red switch and which we use for switching off the circuit.
  • Now after that get connection from normally close switch to normally open switch (green switch) and to contactor normally open auxiliary contacts one side. I sown these connection as thin red line (wire) in the diagram. The wire which will connect to to magnetic contactor normally open auxiliary contact is called the hold wire.
  • Now get the connection from Normally open switch (NO) and connect to the other side of auxiliary contacts ( normally open) contact and to the coil. I shown this connection in above direct online starter diagram as thin blue wire (line).

When you push the normally open contacts switch, direct or touch current will flow to the coil in thin blue wire and starter will set down and when the MC set down, the starter auxiliary normally open contacts make a close connection between one anther and the current will start flowing through the auxiliary contacts. When some one push the normally close switch, by pushing the switch the switch will make a open circuit. And cont actor hold current is also come form the switch, so this time the cont-actor coil will miss the 2nd wire current which comes form the hold wire and contactor will de energize and will not start again until some one did not push the green switch.

After complete wiring direct online starter in panel box, do the incoming connection and out going connection to load. One thing more before you gonna to instill the DOL stater switch OFF your incoming supply and always be care full.
I hope after this post and dol starter wiring diagram now you will be completely understood.

About Sikandar Haidar

Sikandar Haidar is Electrical And Information Technology Student. Who Wants to learn about Electrical and IT Technology and share his experience with people.

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