explain the difference between 3phase 3-wire and 4-wire system?

Answer 1

Typically the term 3 phase 3 wire means the windings are connected in series and identified as delta. The 3 phase 4 wire connection is called grounded wye or star and is connected in parallel. Both connections can be operable either as 3 wire connections or as 4 wire connections. This provides for different voltages to be available. The basic connection of series and parallel do not change however.

Answer 2

A three wire cord has two hot wires, and a ground wire. A four wire cord has two hot wires, a neutral wire, and a ground wire. Electronics will work either way per instructions. The theory is that you will use the old cord from the old stove since it was safe to use this way. But... IF... the neutral becomes disconnected or shorted the stove will continue to operate normally because each hot wire is 180 degrees out of phase. Making the unit a death trap if you touch it and a good ground at the same time. So... much safer to get four wire but okay if you want to use three and are stubborn about recycling.

Answer 3

In a 3 phase system, the three phase coils (Windings) of a generator are brought out and connected to generator terminals and named, as you know, Red (R), Yellow(Y), and Blue(B).
The voltage between any two terminals would be sq root-3 x times the voltage generated in each of the phase windings.

In a 4-wire system, apart from R,Y, and B, the neutral point is also brought out to a neutral terminal. so there are 4 wires---R,Y,B, AND N.Now the voltage measured between any one of the phase winding R, Y, B, and the neutral terminal N would only be the voltage generated in one phase.
Thus, the phase voltage can be 230 volts (What is normally the domestic voltage in India), whereas the line voltage is 400 volts.
---Difficult to explain this without vector diagrams! Clear??

Answer 4

The main difference is the fact that the three wire system has no neutral, and the the four wire system has a neutral.
The only thing i might add to the gentlemans answer is that cable colouring has now changed to Black Brown and Grey, in the three wire method, and Black, Brown grey and blue in the 4-wire.