What defines a '4-wire delta' system in electrical terminology?

A '4-wire delta' system is specifically characterized by being a three-phase system that includes one neutral wire. In this configuration, three phase conductors are connected in a delta formation, while the addition of a fourth wire serves as the neutral. This arrangement allows for balanced loading across the phases and provides the capability to supply both three-phase and single-phase loads.

The presence of the neutral wire is essential for this type of system, as it facilitates the return path for unbalanced loads and ensures proper operation of single-phase loads that can derive power between one of the phases and the neutral. This makes the system versatile and beneficial in various commercial and industrial applications, where both types of loads are present.

The other options do not accurately describe this system. A single-phase system only has two wires, which would not suffice for a three-phase configuration. Four distinct phases imply a more complex arrangement than what is typical for a delta system, and a system with only two wires would not meet the criteria for a '4-wire delta' arrangement, which distinctly requires three phase wires and one neutral.