The minimum acceptable DC megohm resistance of a 4,160 volt motor is approximately?

The minimum acceptable DC megohm resistance for a motor is generally determined based on the voltage rating and the guidelines set forth in industry standards. For a 4,160-volt motor, the commonly referenced rule of thumb states that the minimum insulation resistance should be approximately 1 megohm for every 1,000 volts of operating voltage. Therefore, for a motor operating at 4,160 volts, a minimum insulation resistance of around 4.2 megohms is recommended to ensure reliable operation and safety.

This standard is essential to ensure that the motor's insulation can adequately withstand electrical stresses and prevent leakage currents that could lead to equipment failure or safety hazards. Maintaining a resistance at or above this threshold signifies that the insulation is in good condition, which is critical for preventing short circuits and electrical faults.

The other options do not align with this standard and may indicate either an overly cautious approach or an insufficiently stringent one for that voltage level. Thus, assessing insulation resistance relative to the operating voltage is crucial for identifying an appropriate minimum level to ensure safe and efficient motor operation.