Your new electric motor has reached the facility, you have opened the package and you are ready to connect it to the machine. And it is exactly at this point that the most frequent mistake begins: connecting the motor directly to the grid and running it. Yet a correct commissioning process determines whether the motor runs healthily from the first day, stays within warranty coverage and delivers exactly the life written on its nameplate. In this article we explain, in order, the check steps you should follow from receiving a motor up to the first startup: from insulation (megger) measurement to direction-of-rotation check, from terminal connection to no-load running. As HEM Motor, with our identity as a manufacturer and seller, we also see the correct field commissioning of the motor we sell as part of the job.

This checklist is different from the delivery inspection in which you check whether the motor was damaged in transport; apply our shipping damage checklist, which we address separately, at the moment of delivery, then move on to the first-startup steps in this article. The steps below apply to all three-phase asynchronous motors, from a small aluminium-frame motor to a large cast iron frame motor.

Why is correct commissioning so important? Because the most critical period of an electric motor is the moment it is first run. A significant part of motor failures in the field stem not from the motor itself but from a faulty connection, a skipped insulation measurement, a wrong direction of rotation or poor alignment. In other words, most early failures are of a kind that can be prevented with a few checks lasting minutes. Keeping this article with you like a checklist both extends motor life and protects your warranty rights. Applying the steps in order prevents a skipped check from later turning into a large cost.

Insulation megger measurement and terminal check during electric motor commissioning

Step 1: Visual Check Before Commissioning

Before the first startup, visually inspect the physical condition of the motor. When the shaft is turned by hand, it should rotate freely and without catching, with no abnormal sound. The terminal box cover, gasket and gland inlets must be sound; make sure it is closed against moisture or water ingress. Compare the nameplate information (power, speed, voltage, connection type, IP protection class) once more with your machine's requirements. To make sure you have received the right motor, our nameplate matching guide will be useful. Remember that on motors that have waited in storage for a long time, the shaft bearings may have dried out; in this case turning the shaft a few revolutions by hand before commissioning is good practice.

Step 2: Insulation Resistance (Megger) Measurement

The most critical step of commissioning is measuring the winding insulation resistance. Especially in motors that have waited in storage, remained in a humid environment, or not run for a long time, the windings may have drawn moisture; in this case running it directly causes the winding to burn. Insulation resistance is measured with a megohmmeter (megger).

  • The motor's grid connection must be disconnected and the terminal bridges removed.
  • With the megger, the resistance between each winding terminal and the frame (earth) is measured.
  • The generally accepted rule: the insulation resistance must be above a minimum of 1 MOhm; in low-voltage motors, in practice a few MOhm and above is expected.
  • If the value is very low, the motor has drawn moisture; a drying (heating) process is required before running it.

This measurement is the cheapest insurance that prevents the motor from burning out and takes a few minutes. It is also important for the warranty; because running and burning a damp winding without drying it usually falls outside warranty coverage. You can evaluate what the warranty covers together with our direct replacement and purchasing process.

There are several methods to dry a motor whose insulation resistance reads low: keeping the motor in a ventilated and warm environment, slowly heating the windings with an external heater, or heating by applying a low-voltage controlled current to the windings. After drying, the measurement is repeated and when the value rises above the threshold the motor can be run safely. For motors that will wait in storage for a long time, keeping the storage environment dry prevents this problem from the very start. Especially for motors kept outdoors in the winter months, since they are open to moisture and condensation, the insulation measurement before commissioning becomes even more critical.

Step 3: Terminal Connection - Star or Delta?

The terminal box of a three-phase asynchronous motor has six terminals, and the connection is made as star (Y) or delta (D) with bridges. A wrong connection causes the motor either to produce no torque at all or to draw excessive current and burn out. What determines the correct connection are the voltage values written on the motor's nameplate:

  • Star (Y) connection: The windings are connected to the higher voltage. For example, a motor labeled 400V/690V is connected in star on a 400V grid.
  • Delta (D) connection: The windings are connected to the lower voltage. For example, a motor labeled 230V/400V is connected in delta on a 400V grid.
  • Star-delta starting: In high-power motors, to reduce the starting current the motor first starts in star, then switches to delta. This method is used only on motors suitable for delta operation.

Reading the connection type correctly from the nameplate is essential. We evaluate the problems that high starting current creates on generator-powered sites and the star-delta solution, blending them with our supply to neighboring countries and site-installation experience. When making the terminal connection, make sure the cable lugs are well tightened; a loose connection is the most common cause of heating and sparking.

Three-phase motor star delta terminal connection and direction of rotation check

Step 4: Direction of Rotation Check

Before the motor is coupled to the machine, the direction of rotation must definitely be checked. In applications such as pumps, fans and aspirators, a motor rotating in the wrong direction either does no work at all or loosens the impeller/propeller and causes damage. To check the direction of rotation, run the motor briefly (one or two seconds) and observe the shaft direction. If the direction is reversed, swapping any two of the three phases reverses the direction of rotation. Be sure to do this check without the motor connected to the load, at no load. We also emphasized the importance of the correct direction of rotation in fan and aspirator applications in our HVAC fan motor supply article.

Step 5: No-Load (Unloaded) Running

After the insulation, connection and direction of rotation are verified, run the motor at no load, without connecting it to the load. During no-load running, observe the following: does the motor start smoothly and without jolting, is there abnormal sound or vibration, is there heating or odor coming from the terminal box. A healthy motor running at no load runs quietly and does not vibrate excessively. After running it at no load for a few minutes, if everything is normal, you can move on to the loading step. This step is the last check point for preventing possible damage to the machine.

Step 6: Current, Temperature and Vibration Check

After the motor is connected to the load and starts running, measure the operating parameters. These measurements show whether the motor is loaded correctly and running healthily.

  • Current: Measure the current of the three phases with a clamp ammeter. The drawn current should be below or around the rated current written on the nameplate. Excessive current shows that the motor is overloaded or wrongly sized.
  • Phase imbalance: The currents of the three phases should be close to each other. A noticeable imbalance points to a grid or connection problem.
  • Temperature: The motor frame reaches its operating temperature but should not heat up so much that it cannot be touched by hand. Class F insulated motors are designed to withstand a certain temperature rise, but continuous overheating is a sign of trouble.
  • Vibration: Excessive vibration during operation indicates an alignment error, an unbalanced impeller or a bearing problem.

Recording these values at the first startup allows you to make a comparison later if a failure is suspected. Most problems of the motor overheating and drawing current stem from wrong power selection; for the right power and frame matching, our frame size and power matching guide is a guide.

Step 7: Coupling Alignment

If the motor is connected to the machine with a coupling, the alignment must be done correctly. A faulty alignment shortens bearing life, creates vibration and noise, and causes shaft and seal damage. In alignment, the parallel (offset) misalignment and the angular misalignment are checked separately. Precise alignment made with a dial indicator or laser alignment device is of critical importance, especially in high-speed and high-power motors. In belt-pulley connected systems, the pulleys must be in the same plane and the belt tension must be set correctly. An over-tight belt strains the bearings, while a loose belt causes slipping and efficiency loss. Doing the alignment and tension setting correctly at the first commissioning eliminates the need to intervene again and again later and ensures that the motor delivers its expected life. We also addressed the commissioning and alignment plan for high-power motors in our motor supply above 90 kW article.

After the First Startup: The First Hours and First Days

Commissioning does not end the moment the motor starts running. Especially the first few hours and the first few days are the period in which a possible problem gives its earliest sign. After the first startup, monitoring the following points prevents a small problem from turning into a large failure:

  • Bearing temperature: In the first hours the temperature of the bearing area rises but should stabilize at a point. A continuously rising temperature points to an alignment error or excessive belt tension.
  • Sound character: On the first day, get to know the sound the motor makes. Later, a change in this sound gives an early warning of a bearing or load problem.
  • Current under load: The difference between the no-load current and the current under load shows how much the motor is loaded. The life of a motor running continuously above the rated current is shortened.
  • Connection temperature: Heating of the terminal connections is an indicator of looseness; check on the first day and re-tighten if necessary.

Noting these observations at the first startup ensures you have a reference value in hand later if a failure is suspected. In continuously running applications such as conveyors, this monitoring is even more important; for fast intervention in an emergency stoppage, our conveyor belt motor emergency replacement checklist offers a ready roadmap.

The 5 Most Frequent Mistakes in Commissioning

The mistakes we encounter most in the field and that shorten motor life or cause warranty loss are these. Reviewing this list once before commissioning prevents most problems:

  • Running without measuring insulation: Running a damp winding directly is the most expensive mistake; the winding burns and usually falls outside warranty.
  • Wrong terminal connection: Connecting delta instead of star (or vice versa) without looking at the voltage on the nameplate either does not run the motor or burns it.
  • Checking the direction of rotation while loaded: Doing the direction check while the motor is connected to the pump/fan can loosen the impeller and cause damage.
  • Skipping alignment: Skipping alignment saying "the coupling is flexible anyway" brings bearing and seal failure in a short time.
  • Motor of wrong power: A motor too small for the machine continuously draws excessive current and heats up; a motor too large runs inefficiently and increases the investment cost.

To avoid the last mistake, you need to select the motor power according to the machine's real need; we addressed spare motor planning in our critical spare motor list article.

Choosing the Right Motor Before Commissioning

A healthy commissioning starts with the right motor. A motor of the wrong power, wrong speed or wrong mounting type will cause problems no matter how carefully it is commissioned. In general applications, the standard electric motors and general-purpose industrial motors family, with their B3/B5/B35 mounting options and IP55 protection, meet most needs. You can review all of the efficiency-class and frame-material options in our efficient electric motors category. To select the right speed according to the pole count, our asynchronous motor pole selection guide makes your job easier.

Frequently Asked Questions

Can I run a new motor without doing a megger measurement?

It is not recommended. The windings of motors that have waited in storage or remained in a humid environment may have drawn moisture, and running it directly causes the winding to burn. The insulation resistance measurement takes a few minutes and protects the motor from burning out. If the measured value is below the minimum threshold (generally 1 MOhm), the motor should not be run without being dried. This simple check protects both the motor and your warranty rights and prevents from the start the early failure most frequently encountered in the field.

How do I change the direction of rotation of the motor?

In a three-phase motor, the direction of rotation is reversed by swapping any two of the three phases. In other words, it is enough to swap two phase cables at the terminal with each other. Always do this operation with the power off and the motor not connected to the load. The safest method is to do the direction check at the first startup, before the motor is coupled to the pump or fan, at no load.

Should I connect the motor in star or delta?

This is determined by the voltage values written on the motor's nameplate. On a 400V grid; a motor labeled 400V/690V is connected in star (Y), and a motor labeled 230V/400V is connected in delta (D). A wrong connection causes the motor either to produce no torque or to draw excessive current and burn out. In high-power motors, a star-delta starter is used to reduce the starting current; this method applies only to motors suitable for delta operation. If you are not sure, share the nameplate photo with us and let us determine the correct connection together.

Get a Quote

A correctly commissioned electric motor runs trouble-free from the first day to the last. But the precondition for this is selecting the right motor from the start. Contact us for motors that can be delivered fast from stock, in the power, speed, mounting type and efficiency class suitable for your need. We also provide technical support on commissioning and connection. You can reach us at Phone: +90 (532) 345 49 86 or convey your request through our contact us page. We await your quote request for the right motor selection and delivery times.