Which condition must be maintained for an ungrounded neutral?

For an ungrounded neutral, it is essential that the neutral conductor remains isolated from ground to ensure that the electrical system operates safely and effectively. An ungrounded neutral means that the neutral wire is not directly connected to the earth ground, which helps prevent ground faults and unwanted grounding issues that could lead to electrical hazards.

If the neutral is connected to ground, it could create a parallel path for current flow that could lead to shock hazards or equipment malfunction. By isolating the neutral from the ground, it allows for a balanced load, which is crucial for the proper functioning of electrical equipment. This isolation helps to maintain the integrity of the voltage levels in the system, ensuring that the return path for electrical current remains stable and predictable under normal operating conditions.

The other options provided either suggest connectivity to ground or additional testing requirements, which contradict the principle of maintaining an ungrounded neutral system.