3 Phase Ind Motors

Maybe this is a translation problem, but maybe you are misunderstanding something.

Unless you are using a Star-Delta starting method to reduce starting current, then you don't need to concern yourself with how the motor is connected internally, i.e. Star or Delta, in order to select a motor starter. All you need to do is look at the kW rating at the voltage you are using and select a starter from that. Do not fall into the trap of sizing based upon current only, because induction motor starting involves a number of other issues. Better to use the manufacturer's stated kW ratings.

If you are referring to doing Star-Delta reduced voltage starting, then you still use the same basic information from above, but the 3 contactors are sized differently: 2 of them can be sized at 58% of the motor kW sizing, the other, the Star contactor, can be 33% of the kW rating, however those numbers relate to manufacturer's standard sizes. But I strongly suggest that rather than do a lot of needless work, you simply consult the catalog of your favorite motor starter manufacturer and buy a complete Star-Delta starter assembly, because it will include all of the necessary mechanical and electrical interlocking.

Adding to JRaef's answer ....

If the motor has three leads coming out, whether it is internally star- or delta-connected, you cannot use a star-delta starter. You have to use DOL or, if that is not permitted by the system, some other method of reduced voltage starting. For ΥΔ, you have to have all six leads coming out of the motor.

I think what he means is "how to choose a starter for the star or delta connected motor"

There is a standard in the electrical regulation and of course, it will be different from one country to another country. For small motor up to 13HP (10KW) will be a direct on line starters that is, with DOL Starters.

For motors above the 13HP (11KW) up to 48HP (37KW) you have to use Star Delta Starters and above the 50HP will be Auto Transformer Starters. Then again, now days, soft starter and frequency inverter is more commonly to be used.

Now back to your question.

Motors as everyone knew that, there will be either 3 lead coming out from the motor terminal or 6 lead coming out from the motor terminal. If the motor have 3 lead only that, means the motors is internally "Start Pointed" or "Delta Pointed"

And for motor starter, you can use Direct On line starters or Auto Transformer starters or Soft Starters or Frequency Inverters Starters

Now, if the motor is having 6 lead coming out from the motor, you have to double check the motor name plate and understand what the motor name plate say. These motor that have 6 lead coming out from the motor terminal is for the following function:

1) You can use a DOL Starters for a delta connected motors

2) You can used a Star Delta Starter as the final motor connection is still a Delta connection winding

3) You can use low voltage for Delta connection and for high voltage Star point connection

So Please see the name plate at the motor for more details.