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It is not necessary for unbalanced load (and hence, unbalanced current) to have return path.
Unbalanced loads can be operated under a condition of 3-phase 3-wire systems, however the natural result is a shifted neutral point of which is not connected to the load.
Origional question was "what is the use of neutral in electrical field ".So Iwas assuming 3ph & 4 wire system & tried to reply. Will you pl give correct reply now?
Unbalanced load current can be returned to the supply via the three line wires, resulting in supply's neutral point to be shifted away from the origin (zero volt).
Only a single phase load needs a return path to operate, such a path must be the neutral wire.