Question

necessity of neutral wire​

Answer 1

Neutral is a circuit conductor that normally carries current back to the source
.hope it helps

Answer 2

In a single phase circuit, Live wire is the forward path of current whereas Neutral is the return path of current. hence neutral wire is necessary.
In a 3 phase circuit there are two configuration Star and delta. A circuit can be either star or delta connected.
In star connection we can have a neutral wire but it is not customary to provide one. If you have neutral wire it generally carries no current during normal conditions.During fault conditions neutral wire carries fault current.The neutral point in star connection should be grounded to maintain equal phase voltages.Ground connection to neutral facilitates fault current (zero sequence currents )to ground.
In Delta connection there is no neutral .
Hence Neutral wire is not compulsory in a 3 phase system.

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