Axial Fans

You may start and operate the motor via various electrical equipment, such as: Variable speed drive (vsd), soft starter (ss) and a direct on line starter (DOL)

On each of these units you will have to install a main circuit breaker (mcb) to protect the starter (vsd,ss or dol).The vsd option you will use if you want to vary the speed of the motor/fan (increase or decrease the air flow). The ss option will be used if you want to limit mechanical stress on the driven equipment and also limit the start up current to acceptable limits.

The dol starter (what you refer to as fan starter) may be used when no speed control or current limit are required (normally beter priced than the other 2 options). The dol (integral part of vsd and ss) should have an overload relay (sized according to the full load current of the motor) to protect the motor.

In fact i will use the direct on line while it is simple fan for ventilation but i asking about how i will connect this fan in this case am i use mcb with over load or contactor with overload my bose say a contactor with over load.

regards

<...a contactor with over load...>

...is correct.

i appreciate if leading me to how to select the contactor rating is it right to be 1.25 of the rated current.

i=.5*1000/.8*380*1.72

i=0.95 a

so i of contactor =1.18

what is its rating in this case

Open a dialogue with the suppliers.

You may try to read this article,

http://www.sea.siemens.com/step/pdfs/cc_3.pdf

or

http://www.pacificcoastbreaker.com/files/Moeller%20contactor%20selection%20catalog.pdf

But the advise is always, do not do it unless you are competent of course you are working on a low load only 0.5KVA but check up with the service man and then only go ahead.