What describes a premises wiring system where power is sourced from equipment other than a service?

A premises wiring system that sources power from equipment other than a service is described as a separately derived system. This term refers to an electrical system where the source of power is independent and is not directly connected to the utility service. This can involve generators, transformers, or other equipment that creates a separate electrical source for feeding circuits within a building or facility.

In a separately derived system, the power generation occurs independently, which means that the neutral and ground conductors must be established and managed separately from those of the utility service. This helps ensure proper grounding and fault protection, preventing potential issues such as ground loops or electrical interference.

The importance of having a separately derived system often comes into play in specific applications where isolation from the main service is required for safety or operational reasons. Understanding this concept is crucial for ensuring safe electrical installations, compliance with codes, and the overall safety of the electrical system.