Electrical-Tech

DOL Starter (Direct-On-Line) – Industrial Motor Control Circuit

This schematic represents a standard DOL starter configuration for a 3-phase induction motor operating at 440V.

🔹 Power Circuit:
The motor is directly connected to the supply through an MCCB and Magnetic Contactor, enabling full-line voltage starting.

🔹 Control Circuit:
A step-down transformer provides 220V control supply. The circuit includes:
• Start Push Button (NO)
• Stop Push Button (NC)
• Contactor Coil (A1 & A2)
• Auxiliary Holding Contact (Self-latching)

🔹 Protection:
An Overload Relay (OLR) is integrated to trip the control circuit under overload conditions, ensuring motor safety.

📌 Key Insight:
DOL starters provide high starting torque but also result in high inrush current, making them suitable for small to medium capacity motors.