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ON / OFF 3-Phase Motor Using 8-PIN Relay and DOL Starter

How to Start and Stop a Three-Phase Motor using 8-PIN PLA Relay and DOL Starter?

Three-phase motors are widely used in various industrial applications due to their efficiency and reliability. Properly controlling the operation of these motors is crucial for the smooth functioning of industrial processes. As there are multiple ways to control a single phase and three-phase motor, like DOL starter, Star-delta starter, VFD and PLC based controlling methods, but in this tutorial, we are going to learn the simple way to Start and Stop a 3-Phase motor based on  a combination of an 8-PIN relay and a Direct-On-Line (DOL) starter.

In this article, we will show how to control the ON/OFF operation of a Three-phase motor using both an 8-PIN relay and a DOL starter with wiring, power and control diagrams.

DOL Starter & 8-PIN PLA Relay


A Direct-On-Line (DOL) starter is a type of motor starter that provides a simple and effective way to start and stop three-phase motors. It consists of a contactor, thermal overload relays, and a start-stop push-button station. The DOL starter provides direct connection to the motor windings during the start-up phase, and once the motor reaches its operating speed, the starter switches to the running position.

8-PIN Relay

An 8-PIN relay is an electromechanical switch that can handle higher-power loads using a low-power control signal. In this setup, the relay is utilized to control the operation of the DOL starter, allowing for remote or automated control of the motor.

Components Required

The following components and devices are required to make an ON/OFF control circuit for controlling the Three-phase motor based on an 8-PIN relay and a DOL starter:

  1. Three-Phase Motor
  2. 8-PIN PLA Relay
  3. DOL Starter (based on Contactor & Thermal Overload Relay)
  4. 2-MCB and 3-P MCCB
  5. Control Switches (Start “NO” and Stop “NC”)
  6. Single Phase & Three Phase Supply
  7. Wires & Cables

Wiring, Power and Control Circuit Diagram

Follow these steps to wire the power and control circuit (according to the given circuit) for controlling the Starting and Stopping operation of a Three-phase motor using an 8-PIN relay and a DOL starter:

ON-OFF 3-Phase Motor Using 8-PIN Relay & DOL Starter

  1. Connect the three-phase supply of 415VAC via a 3-P MCCB to the L1, L2, and L3 terminals of the Contactor, O/L relay, and then the 3-Phase motor respectively (wiring DOL Starter).
  2. Connect the 95-NC terminal of the overload relay directly to the Phase (Line) wire from a 2-P MCB.
  3. Connect two pushbuttons in series (RED-NC to Stop and Green-NO to Run) from the 96-NC terminal of the O/L relay. Then, connect the output terminal of the NO-pushbutton to the 2 (Line) and both COM (1 and 8) terminals of the 8-PIN relay.
  4. Wire a jumper from the output of the Red-NC (Stop) push button (or the starting point of the Green-NO switch) to the 6-NO terminal of the 8-PIN relay.
  5. Connect the 3-NO terminal of the PLA relay to the A1 terminal of the contactor.
  6. Finally, connect the neutral wire from the MCB to the A2 terminal of the contactor and the 7 terminal of the 8-PIN relay.
  7. Finally, properly ground the motor, DOL starter, and control circuit to ensure safety.

Operation of Starting & Stopping 3-Phase Motor using 8-PIN Relay & Contactor

  1. Pressing the start button energizes the relay’s coil, which activates the DOL starter’s contactor.
  2. This way, the NC becomes NO and vice versa. But the holding wire (to 6-NO) makes sure continuous latching circuit i.e. removing the pressure from Green (Starting) pushbutton won’t stop the circuit.
  3. When the relay activates, its 3-NO becomes 3-NC which complete the circuit and activate the contactor connected to the O/L relay and 3-Phase motor.
  4. The DOL starter connects the motor windings directly to the three-phase power supply, initiating the motor’s start-up sequence.
  5. The motor accelerates to its rated speed.
  6. Pressing the stop button de-energizes the relay’s coil and holdover the holding circuit to the initial state, deactivating the DOL starter. The motor comes to a stop.

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