Sizing the Cable for Delta Star

If you put the Star Delta controller close to the motor, you only need 1 cable run, and some control wires to the remote stop start buttons, or other control device.

Cable shall withstand fault currents(short circuit and earth fault). Hence sizing shall consider not only full load current but also withstand capacity of fault currents for the time duration of fault.

Actually the motors are only started on Delta & it takes a few seconds to change-over to Star for continuous run. so you need only one size of cable.

Are you sure? Motor is started in "Star" and run in "Delta",not other way? Please reconfirm and advise.

Yes,. Most of the motors is design to run in Delta point. If you have a motor that design to run in Star point, then you cannot use this star/delta starter.

For Star-Delta starter, the motor is always start with star point before change to delta. This is because during the star point, the starting current will be 1/3 of the running current and as soon your motor pick up the speed and the torque, the delta will cut in. For star point, each phase voltage will be to supply to both motor winding that connected in series. R+Y, Y+B, B+R.

Once the motor has changes to delta point, each phase voltage will be supply to each winding only, and this will increase the torque of the motor to its norminal torque. The speed of the motor will remain to its design speed.

Of course, you can also reverse the method of starting with Delta point and change to Star point.

Are you sure that your motor start with Delta and Change to Star????

You're an idiot

John P

I ain't 100% sure but you may want to consider checking up on your cable size once again? :)

Jeeze people, give him a break or don't post if you don't understand the question...

In a Star-Delta starter circuit, you have 6 cables going to the motor from the starter. Each set of cables can be sized at 58% of the motor nameplate FLA, plus whatever sizing rules apply in your neck of the woods.

Being that you used mm², I can tell you are not in North America, but over here we must size motor cables at a minimum of 125% of the intended load. So 58% x 1.25 = 72.5% of the motor nameplate FLA, rounded up to the nearest standard size.

Your sizing rules may be different, I am not a mind reader of anonymous cowards (your words, not mine) so I have no idea where you are.

If in doubt, consult a local qualified Electrician, who will be able to do the calculations, install the equipment, and test and certify it in readiness for handover.