What is a premises wiring system whose power is derived from a source of electric energy or equipment other than a service?

A premises wiring system that derives its power from a source of electric energy or equipment other than a service is classified as a separately derived system. This classification is essential in the context of the National Electrical Code because it establishes specific characteristics regarding the electrical installation and safety requirements.

A separately derived system indicates that the system is independent of the utility service connection. This means that the electrical energy supplied to the system originates from a distinct source, such as a generator or transformer, which is not directly connected to the utility service. This separation is critical for several reasons, including grounding and bonding considerations, which help to ensure safety and prevent electrical shock or fire hazards.

Understanding this concept is crucial for compliance with NEC requirements, as the code outlines the necessary safety measures and configurations for these systems, ensuring that they are installed and maintained with the required rigor. This distinction also aids in determining the applicable rules for overcurrent protection, grounding methods, and the method of electrical distribution within the premises.