What does NEC 430.103 require for a disconnecting means for a motor?

NEC 430.103 specifies that the disconnecting means for a motor must open all ungrounded conductors. This requirement is essential to ensure that the motor is completely de-energized when the disconnecting means is operated, providing safe conditions for maintenance and preventing electrical shock hazards. When all ungrounded conductors are opened, it guarantees that there is no potential difference present that could lead to an unsafe situation for anyone working on or near the equipment.

This requirement is particularly important in three-phase systems, where all three ungrounded conductors must be disconnected to ensure complete isolation of power. Ensuring that all ungrounded conductors are opened also minimizes the risk of arcing or other electrical issues that could occur if only some conductors are disconnected while others remain energized.

For the other choices, opening only grounded conductors does not provide the level of safety necessary, as it would not remove the risk associated with the ungrounded conductors. Opening at least one ungrounded conductor does not fulfill the requirement to safely disconnect all power feeding the motor, leaving some parts potentially energized. Including a fuse for protection is important for overload and short-circuit conditions but does not address the necessity of ensuring that the disconnecting means effectively opens