What describes a premises wiring system that does not have a direct electrical connection to other supply conductors?

A premises wiring system that does not have a direct electrical connection to other supply conductors is accurately described as a separately derived system. This term refers to an electrical system that is generated by a source that is not connected to the supply conductors of the system. Common examples include systems such as transformers that isolate their output from the utility supply, ensuring that the derived power system is independent and does not share grounding or neutral connections with other systems. This setup is essential for applications where electrical isolation is needed for safety, performance, and reliability.

The other terms, while related to electrical systems, do not specifically embody the NEC's definition in the same manner as a separately derived system does. An independent system typically refers to an electrical system that operates without relying on other systems but might still have connections that do not meet the criteria of being separately derived. An isolated system could imply some level of separation, but it may not align with the strict definitions found in the NEC. A stand-alone system often denotes an arrangement that operates independently, but just like the independent system, it doesn't necessarily imply the critical isolation from supply conductors that a separately derived system does.