When is a disconnecting means required for all ungrounded conductors?

A disconnecting means is required for all ungrounded conductors when they supply or pass through a building to ensure safe operation and maintenance. This requirement is crucial as it allows service personnel to isolate electrical equipment from the power supply during servicing, thereby minimizing risk of electrical shock or damage. The National Electrical Code (NEC) emphasizes the importance of having a readily accessible means to disconnect power, which is vital for promoting safety in residential, commercial, and industrial installations.

In situations where conductors pass through a building, the disconnecting means acts as a safeguard against potential hazards that could arise from maintenance activities or during emergencies where immediate de-energization is needed. This requirement supports overall electrical system safety and compliance with NEC standards, which promote the safe use of electricity.

The other options do not capture the comprehensive safety intent of the code; while some scenarios may have specific provisions, the general rule clearly mandates a disconnecting means in this situation.