Which of the following tests is not optional for new AC induction motors in accordance with NETA standards?

The test that is not optional for new AC induction motors according to NETA standards is the space heater test. This test is crucial because space heaters are essential for maintaining the internal temperature of the motor, preventing moisture accumulation that can lead to insulation degradation. Ensuring that the space heater is functional is a part of routine maintenance checks and plays a critical role in the long-term reliability of the motor.

While other tests such as partial discharge, bearing temperature, and vibration are important for assessing different aspects of motor health and performance, they may not be strictly required for every new motor installation. The space heater test, however, is considered necessary to safeguard against environmental factors that could affect the motor's operation.