Direct-On-Line (DOL) starter wiring involves connecting a circuit breaker, a contactor, and an overload relay to the main power supply, control circuit, and the motor Brief By Shri S.K. Vali Sir to Associates.

 Direct-On-Line (DOL) starter wiring involves connecting a circuit breaker, a contactor, and an overload relay to the main power supply, control circuit, and the motor. The control wiring uses a start push-button (typically green, normally open) and a stop push-button (typically red, normally closed) in series with the overload relay's normally closed contact to energize the contactor coil and provide motor protection, with the contactor's auxiliary contact providing a self-holding circuit to keep the motor running after the start button is released.  

Power Circuit

1. Circuit Breaker:

The three-phase power supply is connected to a three-pole Miniature Circuit Breaker (MCCB). 

2. Contactor:

The output of the MCCB is connected to the main power contacts of the contactor (terminals L1, L2, L3). 

3. Thermal Overload Relay:

The output of the contactor (terminals T1, T2, T3) is connected to the thermal overload relay's power terminals. 

4. Motor:

The overload relay's output terminals are then connected to the motor terminals. 

Control Circuit

1. Control Power:

A phase wire is taken from the MCCB or a dedicated single-pole circuit breaker. 

2. Stop Button:

The phase wire is connected to the normally closed (NC) terminals of the stop push-button. 

3. Thermal Relay:

From the stop button, the wire goes to the overload relay's normally closed contact (e.g., terminals 95-96). This contact opens if an overload occurs, de-energizing the coil. 

4. Self-Holding Contact:

From the thermal relay's normally closed contact, the wire connects to a normally open (NO) auxiliary contact on the contactor (e.g., terminals 53-54). 

5. Start Button:

The wire then goes from the contactor's auxiliary contact to the start push-button's normally open (NO) terminals (e.g., terminals 3-4). 

6. Contactor Coil:

The output of the start button is connected to the contactor's coil terminal (A1). 

7. Neutral Connection:

The other terminal of the contactor coil (A2) is connected directly to the neutral conductor of the power supply. 

How it Works

Starting:

Pressing the green start button closes its NO contacts, energizing the contactor coil. The coil also powers the contactor's auxiliary NO contact, which closes and holds the circuit even when the start button is released. 

Running:

The contactor remains energized, keeping its main contacts closed and supplying power to the motor. 

Stopping:

Pressing the red stop button opens its NC contacts, breaking the circuit and de-energizing the contactor coil. 

Overload Protection:

If the motor draws excessive current, the thermal overload relay trips, opening its NC contact in the control circuit, which shuts down the motor.