A Direct Online (DOL) Starter is the simplest way to start an electric motor, connecting it directly to full line voltage for full power, acting as a basic stop/start switch with essential overload protection for small to medium motors (pumps, fans, conveyors). It's reliable, cost-effective, and involves a contactor, circuit breaker, and overload relay, but isn't ideal for large motors due to high inrush current causing supply voltage dips, requiring alternatives like Star-Delta starters for bigger applications.
Working Principle:
When the START push button is pressed, the contactor energizes and full line voltage is applied to the motor terminals. The motor starts instantly with high starting current and high starting torque. If excessive current flows, the overload relay trips and protects the motor.
Main Components:
Contactor
Overload Relay
Start & Stop Push Buttons
MCB / Fuse
Advantages:
Simple and reliable
Low cost
Easy installation and maintenance
Provides full starting torque
Limitations:
High starting current (6–8 times rated current)
Causes voltage dip in supply
Not suitable for large motors
Applications:
Used for small and medium motors such as pumps, fans, blowers, compressors, and general industrial machines.
