Why are there six terminals in a three-phase induction motor?

Answer 1

In 3phase induction motor, stator winding splited into 3windings (Each winding conductor size, no of turns etc are equal to each other). So 3 windings have 6terminal. Generally all 6 terminals are taken out for termination on 5HP and above rated 3phase motors. So, that motor can be started with star / delta starters to reduce starting current (DOL starter does not reduce starting current). Major advantage is It is easy to change the connection (STAR / DELTA) acoording to the purpose going to be used. Also starting and ending terminal to be marked properly.

Answer 2

It depends that which type of starter you are using. If DOL then make DELTA / STAR of motor's 6 terminals to make 3 terminals and then connect that 3terminals to DOLS starter. If STAR DELTA starter means connect all 6terminals to starter.

You have to keep in mind the winding polarities while doing STAR or DELTA and connecting at starter

Answer 3

Every 3 phase motor has three coils (windings), each coil having two terminals, one connected to start of the coil and other to the end. Most* of these motors have all six terminals brought outside.

During starting, motors tend to draw high current, creating stresses on the motors as well as on the supply systems. To reduce these stresses, motor starting current is reduced by connecting the coils in star. Once the motor picks up the speed, motors connection are changed to delta in order to have better load driving capability. Changing the connections from Star to Delta is possible by bringing out all six terminals.

Additional information: . Most of the three phase motors (generally ratings above 2 or 3 HP) have all six terminals brought outside, but some (lower ratings, up to 2 or 3 HP) have only three terminals. The reason is, for lower ratings, the ratio of starting current to rated current is not large.Therefore motors are permanently connected in say Delta.