What must be done to the disconnecting means according to NEC requirements?

The requirement that disconnecting means must be lockable open is crucial for safety and reliability in electrical installations. This ensures that when maintenance or servicing is being conducted, the electrical supply can be safely disconnected and secured, preventing accidental re-energization. Lockable disconnects provide a means to protect maintenance personnel from electrical hazards by ensuring that no one can inadvertently turn the power back on while work is being performed on the circuit or equipment.

This requirement is grounded in safety standards that aim to minimize risks during electrical work. Additionally, it aligns with the broader NEC provisions that focus on the protection of workers and the safe operation of electrical systems.

While other options could relate to specific applications or conditions, they do not encompass the general safety requirement that the lockable feature addresses, which is fundamental to any disconnecting means as defined by the NEC.