Asynchronous Motors

The difference is around 2A per phase.

Elementary my dear Watson! Torque is proportional to applied voltage and in three phase motor, as the applied voltage is more, the torque also would be more. So, also the power remaining same the winding current in single phase motors is Root 3 times more than those in the windings of a 3 phase motor. The heat will be 3 times more in 1 phase motor and hence the frame size to dissipate that heat.

electricalexpert65 - you're still making erroneous arguments about heat produced in motors. I posted recently to an old discussion "Induction Motor Running in Star Connection" started on 5 Oct 2009 commenting on your posts #16 and #17, but no response.

False.

When we say a motor is 1.1kW, that is the MECHANICAL output of the motor, meaning "this motor will put out a specific amount of torque at a specific speed", specifically:

Torque (N-m) = kW x 9550/rpm.

So if the speed is the same, the torque is the same. But you did not specify the speeds of the two motors in question, so any quanitative discussing of torque is impossible unless we ASSume that the speeds are the same.

There is NO RELATIONSHIP in this formula for the electrical power going INTO the motor, what is described as the ABSORBED POWER. That actually will however still be virtually the same. Absorbed power is: Mechanical Output + Conversion Losses (or Mechanical Power/Efficiency). There may be a SLIGHT difference in the Efficiency of a single phase motor vs a 3 phase motor, but at 1.1kW, chances are about equal that the 1 phase motor will have better efficiency rather than worse compared to a 3 phase version.

Raef is correct. On the other hand, if you think of it in terms of magnetic flux "efficiency", the tree phase is always more efficient due shorter flux lines.