Electrical

In a single phase system, the neutral current equals the phase current, except while any protective device is clearing an earth fault.

In a 3-phase system the neutral carries the imbalance current between the three phase currents, except while any protective device is clearing an earth fault.

Does that help?

I think this has been covered a number of times. If you have a knowledge about electricals (or phasors).

Consider the 3 phasors (in 3ph system) or a single phasor in 1 ph system.

The neutral point is the phasor sum of the individual ones, And that is the voltage at which it remains (and in real unbalance systems it can be quite large)

as PWS said, in 1 phse it is quite clear, the current of phase has to go through the neutral.

In multi phase system, the current of one phase gets distributed to other phases with a catch.

If the neutral of the source is connected to the load, it is not necessary that the voltage (ie the phasor sums at that area) will be the same as that at the load (the sum there)

So the two being at different voltage, a part of the current will be diverted through this line too. However if the neutral is not connected (ie floating neutral) then the neutral retains it voltage, and of course no current to flow.

BTW- do not connect the neutral to the earth, unless you have an isolation transformer.