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- 1. Should a 380 V electric motor be connected in star or delta?
- 2. What happens if an electric motor is wrongly connected in delta instead of star (or the other way round)?
- 3. Can a 50 Hz electric motor be used on a 60 Hz supply?
- 4. How does low supply voltage affect an electric motor?
- 5. What happens if an electric motor is left running on two phases (phase loss)?
- 6. Why does voltage unbalance between phases damage an electric motor?
- 7. How do I reverse an electric motor's direction of rotation?
- 8. How is the cross-section of an electric motor cable selected?
- 9. Why is earthing the electric motor frame (PE connection) essential?
- 10. Why does an electric motor draw so much current when starting?
- 11. Which starting method should I choose?
- 12. How is the star-delta changeover time set?
- 13. When is star-delta starting not suitable?
- 14. What is the difference between a soft starter and an inverter?
- 15. What should be checked if an electric motor struggles to start or will not start at all?
- 16. What different needs do an electric motor protection breaker, thermal relay and temperature sensor meet?
- 17. What current should a thermal overload relay be set to?
- 18. What is the difference between PTC and PT100, and how are they connected to the protection circuit?
- 19. How is a contactor selected for an electric motor?
- 20. What should be done if the thermal overload relay keeps tripping?
This guide covers, in question-and-answer form, how a three-phase induction motor is connected to the supply, how it is started and how it is protected: the difference between 230/400 V and 400/690 V on the nameplate, star and delta connection, 60 Hz supply, voltage drop and phase problems, starting methods, thermal overload relay settings and winding sensors.
The answers are based on the values in the HEM Motor 2026 technical catalogue. Electrical connections must be made only by qualified persons; this information does not replace the installation design or the applicable regulations.
To find a motor that suits your connection and starting arrangement, browse the models in the buy electric motors category; the current price is shown on each product page. Share your supply voltage, frequency, starting method and machine details on WhatsApp. If you are replacing an existing motor, sending a photo of the motor nameplate speeds up matching.
Send the motor power, speed, mounting type and quantity on WhatsApp. If you are replacing an existing motor, you can also send a photo of its nameplate.
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