How to troubleshoot 3 phase Induction motor : Step by Step Guide

Last Updated on Jun 24, 2026

Introduction to 3-Phase Induction Motors

Before troubleshooting the 3-phase induction motor, we must know about the 3-phase induction motor, the star-delta starter, and its connection diagram. So let’s take it one by one:

Basic Construction of a 3-Phase Induction Motor

Here we are giving you only an overview on 3 phases induction motor. A 3-phase induction motor has 3 windings; assume U, V, and W. Every winding has its own resistance. But all windings have the same resistance. The total number of wire coming from the motor are 6 i.e., U1, U2, V1, V2, W1, and W2. When these three windings are connected in STAR or DELTA connection (Star delta starter), the motor is ready to start. The connection of the star and delta is shown in the figure.

Now, some questions may be coming to your mind, like

Common Troubleshooting Checks for a 3-Phase Induction Motor

How do we check if the motor is in working condition or not?

Open all connections of the motor. Here, we use a multi-meter or a series tester to check. But by a series tester, we can check only continuity, not accurate resistance.

• If we found infinite resistance or no continuity in any winding, the motor is faulty.
• If we found continuity between the earth and winding, the motor is faulty.
• Check the resistance of the winding. If we found resistance unbalanced or not the same. Motor faulty

Why is the motor drawing more current than the rated current?

Motor is drawing more than rated current due to the following reason:-

• Check the input AC voltage of the motor. Voltage should be in the specification range.
• Check the connection of the motor.
• Check the resistance of the winding. If the resistance of the winding is unbalanced, the motor is faulty.
• Check the mechanical load on the motor. The load should be smooth and not in a jammed condition.
• Disconnect the motor from the load, and check the current. If the current is okay, check the load again.
• Check the rotor by hand or manually; the rotor should be free of any abnormality.
• If the rotor is not smooth, change the bearing of the motor.
• Check rotor alignment.

Also Check: Programmable Control Logic (PLC)

Causes of Motor Overheating

• Improper ventilation or high ambient temperature.
• Low voltage or single phasing.
• The motor is taking a current higher than the rated current without tripping.

Motor Starting Methods

• Direct online starter:- apply direct voltage to the motor
• Star delta starter: reducing voltage at the starting time
• Auto transformer starter: Part winding starting
• Soft starter: reducing voltage at the starting time

What is a Star-Delta Starter

A star-delta starter is the most commonly used starter after a direct online starter in the electrical world. It’s cost-effective and simple operationas compare other voltage-reduced starters.

Most induction motors are started using a direct online starter, but when very large power motors are started using DOL, they take a large starting current. Due to the large current they cause a disturbance in the supply voltage. To limit the starting current flow, large induction motors are started at reduced voltage, and when the motor achieve own rotation speed,  full supply voltage is reconnected. Two methods are used for the reduction of starting voltage are star delta starting and auto transformer starting

A star-delta starter is used to reduce the starting voltage. This also reduces the torque. In this starter, the motor is running in star winding during start, when the motor gets full rpm, the winding converts into a delta winding.

We know that in a star connection, winding voltage is equal to 1/√3 of line voltage, but winding current is equal to line current. That’s why torque is reduced by a factor of three. On the other hand, in a delta connection, winding voltage is equal to line voltage, and winding current is equal to 1/√3 line current.

Also Check: How to design a 5V / 9 V / 12V Power supply

Star-Delta Starter Power Circuit Diagram

6 wire of winding is coming from motor as U1, U2, V1, V2, W1, W2. We have 3-phase line voltage R, Y, B. To make a power connection diagram, we require 3 contactors, 1 overload relay, and 1 MCB. Here, an overload relay is used for protection from heavy current.

Let’s start to make a power connection diagram

Step 1:- line voltage(R, Y, B) connect in the MCB input, and then the MCB output connects to the overload relay input.

Step 2:- overload relay output connected to the main contactor input (C1), and the main contactor output (C1) connects the motor’s three wires as U1, V1, and W1. It means R, Y, and B phases connect to U1, V1, and W1 through the MCB, overload relay, and main contactor. Show in Figure 1

Step 3:- Now we connect U2, V2, and W2 in star contactor output (C3). And all input of the star contactor is shorted with a wire. Using this short wire, we make a star winding as shown in Figure 2.

Step 4:-Now we connect R1, Y1 and B1 with delta contactor (C2). There, we use our mind to connect U2, V2, and W2 in a delta contactor because we want to make a delta winding when this contactor is on. Connect the wire shown in Figure 3. Like U1 connect to W2, U2 connect to V1, V2 connect to W1.

Step 5:- Now merge all the above. Now power connection is ready.

After merging all step showing in Figure 4.

Star-Delta Starter Control Circuit Diagram

Before making a circuit diagram, we know how it works or its working principle.

In this starter, when the motor starts, the motor runs in star connection, which means first of all, the main contactor and the star connector are on. After some time or motor achieves full speed, the motor winding connection converts into a delta connection automatically. It means the star contactor is off and the delta contactor is on. Here, we also provide some interlocks for motor protection in the control circuit. Interlock as follows:-

1. If the main contactor doesn’t on, the star contactor and timer should not be on.
2. Till when star contactor is off, the delta contactor is not on.
3. If the overload relay trips, the starter should be off.

 For making a control circuit diagram, we require one NO push button and one NC push button. If all our contactors and timers are operated on 220V-50Hz, then the control supply requires 220v single phase. Here we can also use 24v operated items, but for 24v supply, also require 24v SMPS. For cost-cutting and easy maintenance, we always use 220V-operated items.

Now we are making a control circuit diagram with the following steps:-

Step 1:- Here we have an AC supply 220v- 50hz (L, N). Line voltage connects to NC point(21) of Overload relay, and goes to NC push button, the NC push button use for stop the starter, and goes to NO push button as per the figure:-

Step 2:- Now connect to the NO push button in this circuit, and also connect to the coil supply (A1) of the main contactor.

Step 3:- now connect the NO point of the main contactor in parallel with the NO push button for holding the main contactor as per figure:-

Step 4: Now connect the timer coil with the NO point of the main contactor(C1) to the X point.

Step 5:- and connect the star contactor (C2) with the NO point of the main contactor and the NC point of the timer to the X point. For interlocking with the delta contactor, also connect the NC point of the delta contactor (C3). Do Connection as per the figure:-

Step 6:- Now connect the delta contactor with the NO point of the timer and the NC point of the star contactor.

Also check: Relay Logic Circuit

How the control circuit works:-

Step 1:- Here, the line voltage comes to the start push button(PB2) through the overload relay(OL) and the stop button(PB1). When we push the PB1 button, the supply goes to the C1 contactor coil supply. The auxiliary contact of the main contactor coil (C1), which is connected in parallel across the Start push button(PB2), will become NO to NC. This provides a means to hold the main contactor coil activated, which maintains the control circuit active even after releasing the start push button(PB2) switch.

Step 2:– When the main contactor is activated, the star contactor and timer are also activated. The timer activates through auxiliary NO contact of the main contactor. The star contactor is activated through the auxiliary NO contact of the main contactor and the NC contact of the delta contactor.

Step 3:– Here we set the time of the timer, after which the time. The timer contact changes from NO to NC and NC to NO. So the NC point, which is connected with the star contactor in series, becomes NO. The star contactor deactivates, and when the star contactor is off, the delta contactor is on because the timer NO contact becomes NC.