How many conductors should be simultaneously disconnected by a service's disconnecting means?

The requirement to simultaneously disconnect all ungrounded conductors from a service's disconnecting means is based on safety concerns and electrical code regulations. By ensuring that all ungrounded conductors are disconnected, the risk of electrical shock or arcing is minimized for anyone working on the electrical system.

This practice aligns with the National Electrical Code (NEC), which emphasizes that all supply conductors need to be disconnected to provide complete and safe access to circuits during maintenance or repairs. Disconnecting only some conductors would leave potential voltage present, posing a danger to personnel.

In this context, grounding conductors, or simply disconnecting one conductor, does not provide the same level of safety. Grounded conductors need proper handling, but their disconnection alone doesn't guarantee a safe working environment when other power sources are still connected. Thus, the most comprehensive and safest approach is to disconnect all ungrounded conductors, ensuring that the entire circuit is open and safe to work on.