Electronic – Does the neutral wire have any voltage

neutralpowerpower supplythree phasewire

In this article, the author talks about 3 phase and the magic of a missing neutral wire. And there's the following paragraph:

In a 3-phase system the voltage between any two phases is 3 times higher than the voltage of an individual phase by a factor of 1.73 (square root of 3 to be exact). If your X-N (and Y-N and Z-N) voltage is 120V (common in the US), the X-Y (and Y-Z and Z-X) voltages (a.k.a. “cross-phase” voltages) will be 120V * 1.73 = 208V.

When he says the X-N voltage is 120V, with N being the reference voltage, is the reference voltage 0V or does it have some value?

From the diagram (in the link,) I realise that the neutral wire is grounded, but is this the same as earth grounding? Doesn't the neutral wire go back to the transformer so as to provide a closed circuit?

Best Answer

The neutral wire is defined to be 0V. And each phase individually has a voltage relative to neutral of 115V if you are in the US, and 230V if you are in most of Europe.

But because the three phases are 120 deg out of phase compared to each other this results in a voltage difference of 115V * sqrt(3) = 200V (or 230V * sqrt(3) = 400V) between any two phases.

Depending on the type of mains distribution system you've got in the country you live (I don't know how it is in the US) the neutral wire might be connected to earth at the power company. Keep in mind however, that even though the neutral wire might be connected to earth, this doesn't mean that it is actually at earth potential, because a return current might be flowing in the neutral wire, and due to the resistance in the wire this will cause a voltage at your end of the neutral wire.

It is also important to keep in mind that in many countries the mains plugs we use can actually be turned 180 deg putting line where neutral was supposed to be, meaning that with these kinds of systems you can never be sure if your neutral is actually neutral or line (BE CAREFUL!)

So to sum it up: The neutral wire is defined to be 0V. But will typically be at some voltage potential (relative to earth).