Explanation of European 3-phase AC networks. It is too easy to understand, just some attention. Here we have 3 hot wires, one neutral and one ground on image. Any hot wire to neutral gives 230 Volts and any hot wire to any opposite hot wire gives 400 Volts. If we disconnect neutral, all devices will be damaged by overvoltage - that is why ground wire should be lined separately from neutral.
<a href="//commons.wikimedia.org/wiki/User:Dmitry_G" title="User:Dmitry G">Dmitry G</a>
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<span class="int-own-work" lang="en">Own work</span>