When is an alternate AC power source considered a separately derived system?

An alternate AC power source is considered a separately derived system when the grounded conductor is not solidly interconnected with other systems. This means that the system is electrically isolated in such a way that it has its own grounding method and does not share its grounding system with other electrical systems. This isolation is crucial for ensuring that ground faults or issues in one system do not affect the integrity or safety of other systems.

This characteristic allows for safer operation as it prevents the unintended flow of fault current between different systems, which could pose safety hazards and complications in electrical performance. By having a grounded conductor that is not interconnected, this system maintains its operational integrity independently, which is a key principle in grounding and bonding practices.