In a symmetrical three-phase four-wire, wye system, the three phase conductors have the same voltage to the system neutral. The voltage between line conductors is √3 times the phase conductor to neutral voltage: The currents returning from the customers’ premises to the supply transformer all share the neutral wire.
What does it mean neutral wire required?
The most common requirement of any hardwired automated light switch is a neutral wire. This is a diagram of a switch with a neutral. The black “hot” connection is broken to turn the light on/off, the white “neutral” connection completes the circuit. The bare (hopefully) solid copper wire is the ground.