Where is the return path for three phase current?

The current in one phase splits and returns via the other two phases. This is a constantly changing dynamic process best described by using a 3 phase waveform graph. You will then see what is happening.

In two phase power one line is + while the other is -. One forces current while the other returns current. there is no current in the neutral line.

In three Phase power the situation is very similar; One or two lines are + while 1 or 2 lines are -. the + lines force current whild the - lines return current and there is no current in the neutal line. The neutral line is simply a safety connection for current in the Frame.

In USA we have DELTA and WYE 3-phase power.

Delta uses the next phase for the return.

3 wires plus ground.

Wye has a neutral.

4 wires plus ground.

For a balanced load, currents separated in phase by 120° sum to zero. When the load is not balanced, amperage is detected in the neutral.

With alternating voltage each leg becomes both source and return half the time.

the other 2 phases. Goto any 3 phase distribution board measure the current on the actives then measure the current on the neutral