Why neutral is absent in 3 phase connection?
Neutral is absent in 3 phase connection because it is not needed for balanced loads, such as 3 phase motors or heaters.
Balanced loads are electrical loads with 3 phases that have the same resistance or impedance, so they draw the same current in each phase.
The sum of the currents in the three phases is zero, so there is no current in the neutral wire. Therefore, the neutral wire can be omitted in 3 phase connection for balanced loads².
However, neutral is present in 3 phase connection for unbalanced loads, such as single-phase loads that need a return path for the current. Neutral also allows the connection of both 3 phase and single phase loads to the same 3 phase supply.
Neutral provides two voltages from the 3 phase supply: the line voltage and the phase voltage. For example, in Australia, the line voltage is 400V and the phase voltage is 230V¹.
This means that a 3 phase load can have either 400V or 230V across each phase, and a single phase load can have 230V across one phase and neutral.