A disconnecting means is required for all ungrounded conductors under what condition?

• A. If they supply a building or pass through a building
• B. Only if they supply a building
• C. Only if they pass through a building
• D. Never required for ungrounded conductors

Answer: (A)

When working with ungrounded conductors, you must have a readily accessible way to disconnect the entire feeder so you can safely de-energize the system for maintenance or in a fault. The requirement applies whenever those ungrounded conductors either supply a building or pass through a building. This ensures that, at the building boundary, there is a means to isolate the ungrounded supply whether it’s entering the building to feed it or simply routed through it. If the conductors only supply or only pass through, that isolation still needs to be available; the rule isn’t limited to just one of those situations, and it isn’t never required.