Heating, Ventilation, and Air Conditioning (HVAC ) Electrical Practice Test

When checking the windings of a three-phase motor, what should be observed?

1. All three terminals should show different resistance

2. Only two terminals should show resistance

3. All three terminals should show the same resistance

4. Resistance should decrease with load

The correct answer is: All three terminals should show the same resistance

When checking the windings of a three-phase motor, it is important to observe that all three terminals show the same resistance. This indicates that the windings are balanced, which is essential for the proper operation of the motor. Balanced windings ensure that the motor runs smoothly, efficiently, and generates an even torque. If the resistances were significantly different, it could indicate a problem such as a damaged winding or a short circuit, which could lead to poor motor performance, overheating, or damage. Thus, uniform resistance values across all three terminals suggest that the windings are intact and functioning as intended, supporting the motor's capability to operate effectively under load. In contrast, observing different resistance values could suggest imbalance or faults within the motor, which would be detrimental to its operation.