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I have a relatively simple question on the grid voltage. When we say the voltage from the wall is 220 Vrms is that the line-line voltage or is that the phase voltage. ie are the two output lines from a socket both hot (in which case each line’s magnitude would be 220/sqrt(3) Vrms) or is one hot and the other neutral?

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When we say the voltage from the wall is 220 Vrms is that the line-line voltage or is that the phase voltage

Usually, the output winding at the substation that feeds domestic buildings is a Y formation. This means it produces three phase voltages and one neutral. What should be wired to a wall socket is one phase voltage (live) and the neutral.

But there are variations and what I've described above is typical for UK outlets.

So, if the phase voltage is 230 volts (UK), the line (or phase to phase) voltage is \$\sqrt3\$ higher at 398 volts. If the phase voltage is 240 volts then the line voltage is 415 volts.

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    \$\begingroup\$ One notable exception is Norway which uses 230 V line-line voltage, don't distribute neutral and have two fuses for everything to protect against if one phase faults to ground. \$\endgroup\$ – winny May 27 at 10:24

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