Wiring of DOL Starter for Automatic / Manual Control Using Digital Timer

Electrical Technology

How to Control a 3-Phase Motor Using DOL Starter and Digital Timer for Automatic and Manual Operation

Controlling a three-phase motor is a crucial task in many industrial applications. One common method is using a Direct-On-Line (DOL) starter, combined with a digital timer, to achieve both automatic and manual operation. This article provides a comprehensive guide on how to control a three-phase motor using a DOL starter and digital timer, highlighting the key components, wiring connections, and operational modes.

Three-phase motors are extensively used in various industrial applications due to their efficiency and reliability. Controlling these motors requires a suitable starter mechanism that ensures safe and efficient operation. A Direct-On-Line (DOL) starter is a common type of motor starter that provides the necessary control for starting and stopping the motor. By combining a DOL starter with a digital timer, we can achieve automatic and manual control of the motor, enabling enhanced functionality and flexibility.

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Table of Contents

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Components Required

To control a three-phase motor using a DOL starter and digital timer, the following components are required:

Three-phase motor
DOL starter
Digital timer
Contactor
Overload relay
MCB – 3P, 400V
MCB – 2P, 230V
ON OFF Selector Switch
400V – Three Phase AC Supply
230V Single Phase AC Supply
Wires, cables, switches and indicators: Manual control switches (such as start, stop, and reset buttons) and indicator pilot lights (for status indication).

Wiring & Control Diagram

Proper wiring connections are crucial for the safe and effective control of the three-phase motor. The following steps outline the wiring connections required for controlling the motor using a DOL starter and digital timer as shown in below figure:

Click image to enlarge

Step 1: Power Supply Connections

Connect the three-phase power supply lines (L1, L2, L3) to the DOL starter’s main terminals (typically labeled 1L1, 3L2, 5L3) on the main contactor and associated relay.

Step 2: Motor Connections

Connect the motor’s three phases (U1, V1, W1 or R, S, T) to the DOL starter’s motor terminals (typically labeled 2L1, 4L2, 6L3).

Step 3: Control Circuit Connections

Connect the control circuit wiring to the DOL starter as shown in the wiring and control diagram. to do so,

Connect the digital timer’s to 230V CB (usually labeled 1 & 2) and control wires to the appropriate terminals on the DOL starter as follow.

5-NO to the NO 1 – ON button and NO -13 and A1 terminal of contactor.
Connect the NO 2 – ON button to the “M” for manual terminal of selector switch and NO – 14 on contactor.
Connect the NC – OFF button to the selector switch and 95 terminal on contactor.
Connect the C “4” terminal from digital programable timer to the “A” for automatics terminal on selector switch.

Operational Modes

The combination of the DOL starter and digital timer allows for both automatic and manual control of the three-phase motor. This section describes the operational modes and their corresponding control sequences:

Manual Operation Mode

Rotate the knob on selector switch to the “M” terminal for manual operation.
Press the “Start” button to energize the DOL starter’s coil which closes the main contacts.
The motor receives power, starts running, and continues running until the “Stop” button is pressed.
Pressing the “Stop” button de-energizes the DOL starter’s coil, opening the main contacts and stopping the motor.

Automatic Operation Mode

Rotate the knob on selector switch to the “A” terminal for automatics operation.
Set the desired time duration on the digital timer.
Press the “Start” button to energize the DOL starter’s coil which closes the main contacts.
The motor starts running and continues running for the preset time duration.
After the preset time elapses, the digital timer triggers a control signal.
The control signal de-energizes the DOL starter’s coil, opening the main contacts and stopping the motor.

Safety Considerations

When working with three-phase motors and their control systems, it is essential to prioritize safety. Consider the following safety considerations during installation and operation:

Disconnect the power supply before performing any wiring connections or maintenance tasks.
Ensure proper electrical grounding of all components.
Adhere to local electrical codes and regulations.
Use appropriate personal protective equipment (PPE) when working with electrical systems.
Regularly inspect and maintain the motor control system to ensure proper functionality.
Verify the contactor’s coil voltage compatibility with the control circuit voltage.
Adjust the overload relay settings according to the motor’s specifications to provide appropriate protection against overloads.
Ensure proper grounding of the control circuit.
Confirm that the motor connections match the corresponding terminals on the DOL starter.
Ensure proper tightening of the connections and use appropriate wire sizing to handle the motor’s current.
Use appropriate wire sizes and connect the start, stop, and reset buttons to their respective terminals on the DOL starter.

Summary

Controlling a three-phase motor using a DOL starter and digital timer provides an effective solution for achieving both manual and automatic operation. By following the wiring connections and understanding the operational modes, it is possible to implement a reliable motor control system suitable for a wide range of industrial applications. Safety considerations must be emphasized throughout the installation and operation to ensure the well-being of personnel and the longevity of the motor control system.