You are troubleshooting a 480 V, 3-phase motor that is running excessively hot. You measure the current in each phase and obtain 25 A, 28 A, and 35 A. The motor's nameplate FLC is 30 A. What is the most likely cause of the overheating?

Question: You are troubleshooting a 480 V, 3-phase motor that is running excessively hot. You measure the current in each phase and obtain 25 A, 28 A, and 35 A. The motor's nameplate FLC is 30 A. What is the most likely cause of the overheating?

Answer options: ✅ Unbalanced phase currents causing excessive losses.

• The motor is significantly overloaded.
• Loose connections in the motor termination box.
• High ambient temperature around the motor enclosure.

Correct answer: Unbalanced phase currents causing excessive losses.

Explanation: The measured currents show a significant unbalance (10 A difference between the lowest and highest phase current), which can cause disproportionate heating in the motor windings due to negative sequence currents. While the average current (29.3 A) is near FLC, the unbalance is the primary concern here. Overloading would typically show all three phases significantly above 30A. Loose connections might cause heating at the connection point rather than throughout the motor windings, and high ambient temperature would be a general factor, not specific to unbalanced current.