motor

In a single phase motor you required neutral.

In a 3 phase motor you don't required natural, due to vector sum of 3 phase is zero. Hence there is no return path required.

A 3-phase motor connected in 'delta' does not need a neutral wire. If it were connected in 'star' then a neutral wire would be needed.

http://en.wikipedia.org/wiki/Three-phase_electric_power

<in 'star' then a neutral wire would be needed.>

STAR POINT IS INTERNAL.

Neutral is not connected to any motor I have seen.

I must respectfully disagree with you on this one. Even when a motor is connected in star configuration, no neutral wire is required. The phase windings are connected at the center of the star, but no external connection is needed at this point. In fact, most industrial motor control centers are supplied by a transformer using a delta-connected secondary, eliminating the possibility of a neutral connection.

The purpose of the neutral conductor in a 3 phase system is to provide a return path for imbalance of the current in the phase conductors. There will be no significant imbalance in a properly operating motor, as the winding configuration provides uniform field density through 360° of rotation. If there were a phase current imbalance (due to a bad connection, winding, etc), the motor would experience unbalanced torque, resulting in improper operation and possible damage.

As post 3 and 4

Neutral is not connected to any motor I have seen.

Depends on what type of motor you are referring to.A lv 3 phase motor can run on Delta so no neutral is required. In HT motors which almost always have their stator in star connection have a separate terminal box for neutral which is brought out.In star connected lv motor neutral normally not brought out.having a neutral depends upon the type of winding connection and whether required to be brought out depends upon the degree of protection.