I have been asked to "The process of wiring a star/delta starter." I know the theory and understand what is happening but don't understand how to explain the wiring of it.

Any help?

Assuming the starter is already wired up, and just has 6 terminals available for the motor and three for the supply, or do you have to describe the wiring of the contactors and timer?

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David
CEng etc, don't ask, its a result not a question!

Something I learned recently,set the overload at 58% of flc,not 100%.
Regards hz

I think you will find, that is the change over timer for the star to delta contactor. Not the overload

the overload should only be set at 58% motor FLC if it is wired in the delta loop, In some circuits the overload is wired so it still carries the motors FLC

But to work out which is which you need a proper understanding of a start delta starter

I tasked two of our younger electricians with drawing the diagram (without cheating) of the whole starter complete with the interlocks and timer wiring..... the results were to say the least "in need of a bit of correction"

Stu

Dave,I ordered a sd starter from rs recently complete with derated overload which was correct,but it seems a pain that the starter could have been wired in a different way making the overload unsuitable.
Regards hz

The problem with putting the overloads in the line rather than the delta feed is during starting the overload isn't providing adequate protection.

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Could there be a better way?

In theory yes, but in practice?

Or 5 mins on wiki. If the O/L is in the delta loop then the square root of 3 comes into play. And with the starters I've come accross this is its normal place.
So as pointed out by OP 58% correction of FLC is used.
I have noticed on larger motor starters the O/L is not in the star circuit and only comes into play in delta. Also information I have indicates the change over speed should be at 80% of full speed not the 58 I thought it was.

Just to be clear DOL starter over loads are rated at FLC of motor.

But so are delta ones, the motor FLC is still important!I think you may haver missed a point here.

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David
CEng etc, don't ask, its a result not a question!

a motor only runs in star for a couple of seconds so the overload is not important, the full load current is important as far as the fuses protecting it are concerned

once you look at a standard diagram for star delta you can see the overload has phase current passing through it when in delta and not the full line current. Obviously the supply fuses would be selected in line with manufactures documentation.



It depends on the mass being rotated, we have some that take several minutes before theuy gain enough speed before you can change into delta. If the change over happens to soon it blows the supply fuses normally very quickly. Thats from my experience