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In three-phase the 2nd and 3rd phase are offset by about 120 degrees(\$\frac{2\pi}{3}\$ radians). But how is this achieved?
The concept that just each phase is offset by 120 degrees sounds easy but designing a circuit for this looks more difficult.
Does it go back to when the electricity is generated at the power station or done later on in the transmission?
For example each generator is configured to generate one phase slightly later than another?
When there's 120° between phases the sum of the voltages at any time will be zero.
This means that with a balanced load no current flows in the return line (neutral).
Also, if each phase is 230V with respect to the neutral (star operation), then there will be 230V \$\times\$ \$\sqrt{3}\$ = 400V between any two phases (triangle or delta operation), and they're also equally spaced, i.e. at 120° angles.
(images from http://www.electrician2.com/electa1/electa3htm.htm)
The Onesto KRC3 is a residual current circuit breaker and these types of devices operate by measuring a difference current flowing in live and neutral rather than specifically measuring a leakage current to ground.
ONESTO KRC3 230/240V 25A 300mA KRC3 Residual Current Device Leakage protector Circuit breaker
The above description is taken from here
The difference between live and neutral currents IS earth current in effect: -
As you can see from the above, EARTH is included but isn't needed and some devices down provide a thru-going connection for earth at all. In north America they are called ground fault circuit interrupters: -
Best Answer
There are 3 phase alternators that produce a 3 phase supply which is then transmitted over 3 or 4 wire systems.One first needs to understand how a single phase voltage is generated based on Faraday's laws of electromagnetic induction.The generated voltage is, among other things, also dependent on the (sine of the) angle between the magnetic field and the coil in which the voltage is induced.Now in a 3 phase generator, the the magnets and the coils are aligned (mechanically) in such a way that the angles are 120 degrees apart.Consequently, the instantaneous voltage of each phase offsets the other phases by 2π/3 radians.