If the electric motor does not start, in 90% of cases the cause can be found in 15–30 minutes using a conventional multimeter and current clamps. The main thing is to act systematically, from simple to complex, and not immediately disassemble the car. This 10-step checklist is based on the experience of the Elektromotors service center in Tashkent - it is suitable for asynchronous motors 0.75-110 kW AC 380/220 V.
Before diagnostics: safety precautions
Any work with an electric motor begins with a shutdown. Remove the voltage at the input circuit breaker, hang a “Do not turn on” sign, check the absence of voltage with an indicator on all three phases. Only then start checking. Never work with live windings - even when the motor is switched off, charges may remain from the reactive power compensation capacitors.
10-step checklist
Step 1. Availability of power at the input
Using a multimeter or indicator, check the voltage at the terminals of the control cabinet input circuit breaker. The norm for a three-phase network is 380 V ± 10% between phases, 220 V between phase and zero. If at least one phase is missing, the problem is on the side of the supply network or the input circuit breaker; the problem has not reached the motor. Danger: running the motor on two phases leads to overheating and burnout of the winding within 5–15 minutes.
Step 2. Fuse status
Inspect the fusible links in the cabinet. A blown fuse is not a cause, but a consequence: there is a short circuit or overload somewhere. Replace the insert only after the root problem has been eliminated. Test all three fuses with a multimeter for resistance - it should be close to 0 Ohm.
Step 3. Circuit breaker
Check whether the thermal or magnetic release has tripped. Turn on the machine again. If it turns off immediately, the engine has a short circuit or a jammed rotor; further attempts to start it are dangerous. If the machine holds, but the engine does not move, go to the next step.
Step 4. Contactor and thermal relay
When you press the “Start” button, the contactor should clearly click. If there is no click, the problem is in the contactor coil, button or control circuit. If the contactor turns on, but the motor does not rotate, check the powerful power contacts for burning and sticking. Test the contacts with a multimeter in the closed state: the resistance should be less than 0.1 Ohm.
Step 5. Thermal relay
If the thermal relay is triggered, it blocks the start until manual reset. Click the Reset button and try again. Repeated operation means a real overload: check the current in the phases with a current clamp and compare with the nominal value on the nameplate. An excess of even 15% is a reason to look for a mechanical problem with the drive.
Step 6. Starting and running capacitor (single-phase motors)
For single-phase 220 V motors, a faulty capacitor is the No. 1 reason for starting failure. The engine hums, but does not rotate, or rotates by hand, but does not accelerate. Measure the capacitance of the capacitor with a multimeter in “F” mode. A deviation of more than 20% from the rating on the nameplate means the capacitor needs to be replaced. Danger: working on a faulty capacitor leads to overheating of the starting winding.
Step 7. Stator winding resistance
Remove the jumpers on the terminal box. Ring each of the three windings separately. The resistances should be the same with a spread of no more than 5%. If one winding shows a break (infinity) or a short circuit (close to 0), the motor requires rewinding the winding. Self-repair of the winding is almost impossible.
Step 8. Insulation resistance
Using a 500 or 1000 V megohmmeter, measure the resistance between the windings and the housing. The norm is at least 1 MOhm for motors up to 660 V. A value below 0.5 MOhm means moisture or insulation breakdown. A motor with broken insulation is deadly - the housing is live, and electric shock is possible. Urgent rewinding of the stator or drying of the windings is required.
Step 9. Jamming of bearings and rotor
With the power off, try turning the motor shaft by hand by the clutch or pulley. A healthy engine turns over with slight resistance. If the shaft does not move, the bearing is jammed, or the rotor is touching the stator. It is forbidden to turn on the engine by force through the relay - the winding will burn out in seconds. Requires disassembly and bearing replacement.
Step 10. Control circuit and push-button station
If everything in the power supply is working properly, but the contactor does not turn on, look for an open circuit in the control circuit. Ring the “Start” and “Stop” buttons, contactor block contacts, and self-retaining circuit. Often the problem is oxidized contacts of the button post or a broken wire in the flexible cable of the suspension.
Table: symptom - cause - action
| Symptom | Probable cause | What to do |
|---|---|---|
| Motor is silent, contactor does not click | No power, control circuit is faulty | Steps 1–4, 10 |
| Humming, but not rotating | Phase loss, faulty capacitor | Steps 1, 6, 7 |
| The machine immediately knocks out | Short circuit of the winding or wedge jamming | Steps 7, 8, 9 |
| Thermal relay is triggered | Overload, interturn short circuit | Steps 5, 7 |
| Smell of burning, smoke | Winding burned out | Urgently contact a specialist |
| The shaft cannot be turned by hand | Bearings are jammed | Step 9, repair |
| Electric shock from the case | Insulation breakdown on the case | Step 8, turn off immediately |
When to call a specialist
Some of the checks can be safely performed by the company's in-house electrician. But there are situations when self-diagnosis is life-threatening and can aggravate the breakdown. Call an Elektromotors engineer in Tashkent if:
- motor power over 30 kW - there is enough short circuit energy to cause serious injury;
- insulation resistance is below normal - needs drying or rewinding in a specialized workshop;
- phase-to-phase short circuit protection has tripped - there may be burnt-out stator iron inside;
- the engine is installed in a hard-to-reach place - at a height, in a basement, in an explosive area;
- we are talking about taps, elevators, water intake pumps - where the cost of downtime is higher than the cost of urgent repairs.
For asynchronous motors up to 110 kW, we offer on-site visits to Tashkent and its suburbs within 2-4 hours. A complete diagnosis takes 1 hour, after which the customer receives a defective statement and estimate. More information about the service can be found on the page repair of asynchronous electric motors.
How to avoid repeated refusals
Most starting failures recur if only the symptom is addressed and not the cause. After any repair, be sure to:
- Measure the current in each phase under load - it should be symmetrical with a spread of no more than 5%.
- Check the tightness of all terminal connections - a weak contact heats up and eventually burns out.
- Adjust the thermal relay setting exactly according to the nameplate current, and not “with a margin.”
- Blow out dust from the control cabinet and engine every six months - especially important for dusty industries in Tashkent.
- Keep a log of protection activations - repeated events indicate a hidden defect.
We will help you start your engine
If, after passing the checklist, your electric motor does not start, contact Elektromotors engineers. We carry out urgent engine repairs in Tashkent with on-site visits, diagnostics in 1 hour and a recovery period of 1 working day. All work is guaranteed for 12 months. Leave a request or call - our engineer will contact you within 15 minutes.