Which Connection to Motor 5HP or Above, Star or Delta in DOL

"A Direct-On-Line (DOL) starter is an electronic 3-phase motor-control system which offers soft starts in DELTA configuration. DOL starters are now replacing the use of manual or semi-automatic "star-delta" starters.

Read more: http://wiki.answers.com/Q/What_is_a_DOL_or_direct_on_line_starter_and_how_does_it_work#ixzz1m2iWbKKX

"To start a motor direct on line (DOL) in delta requires approximately 6 to 8 times the full load current of the motor and delivers full torque. Delta places 415v across each of the windings on the motor. A Star-Delta starter starts the motor in Star which places 240v across each winding on the motor. This results in a lower starting current and also a lower starting torque.

Read more: http://wiki.answers.com/Q/What_is_the_advantage_of_a_Star_Delta_Motor_Starter#ixzz1m2lRly8l

That ↑ cannot be a star-delta starter, as the motor needs 6 leads. The diagram only shows three.

You can connect up to 45 Hp with DOL starter,even though star delta is recommented.

If starting current in DOL/across the line starter is high you may use a shunt capacitor or auto transformer starter to avoid switching surge during changeover from star to delta.

The DOL starter which is commonly available in the market are not the one shown in the drawing of Mr. SolarEagle. The one in the drawing is an advanced version of DOL, which is better than star-delta starter.

It is advised to use Star-Delta starting for motors above 5HP. This is to limit the high staring current of motor, which in turn cause a voltage fluctuation in the whole system.

Motor connection is always DELTA , to get maximum output from motor.

Correct answer.

The size of your supply will determine the method you use to start your motor.

In the first few seconds the motor can easily draw 8 times its normal running current. This temporary overcurrent will cause your supply voltage to dip - could cause brown outs - might in turn cause other equipment to trip out.

In your capacity as engineer you should know the magnitude of your supply.

another thing to be aware of is the voltage rating of the motor. It might be wound such that in star its good for 690V and 400V in delta. This should be on the name plate.

Why do you want 690V rating for star connection,if phase to phase voltage is 400 in delta connection?.

It depends on your motor and where you live. In the USA and Canada the majority of electric motors under 100 HP are factory built as double wye 9 lead connection types for 230/460 VAC input which does not give you a choice on how you set them up.

Everyone except tcmtech has, I believe, misinterpreted your question. As I see it, you have a motor, which you intend to start via a DOL stater, but it has two connections available INSIDE of the motor; Star or Delta. This would be because it is a dual voltage motor. Being that you used the term DOL, I can assume you have an IEC motor, in which case it will be 230/400V (or 220/380 or 240/415, it's all the same really).

If your supply voltage is the lower one, i.e. 230V nominal, you connect the motor in the Delta configuration.

If your supply voltage is the higher, i.e. 400V nominal, then you use the Star configuration.

G.A No.9, I have seen many motors burn because they were connected star or Delta because of size , but it is very clear on the motor nameplate the method of connection depending on supply voltage.