What does with respect to the neutral wire mean…..?
The question is a bit fuzzy, so I will try to give all possible answers: When you are doing any measurements, you need a reference to specify what the measurement is referenced to. The neutral wire is nominally connected to earth somewhere, so should in theory be the same as measuring to ground – but in practice, there is usually a small voltage difference to ground due to voltage drops with current flow. If you are talking about the AC supply itself, think of it as a battery supply to a lamp, with the two connections at the battery being swapped continuously. You still get the same voltage at the lamp, and the lamp works just the same – but if taking a measurement, you will find it’s the same voltage all the time, but the polarity is continuously swapping (because the battery wires are being swapped). That is, in principle, an AC supply (though usually AC alternates smoothly rather than being sharply switched). For safety, one ‘leg’ of the AC wiring is connected to earth, generally at
