In three phase system the load on 2 phases is 10 , 10amp and in a third phase is 0amp, so how much current in a neutral ?

neutral current is Zero

Dear Hassan,

Am afraid your question is not complete. In three phases systems we are unable to do victorial analysis (adding and subtracting phases) without having information about both magnitudes and direction.

In other words, you have not given information about the direction of the current passing through the other two phases and therefore no one is able to tell you what is the resultant vector in neutral !

now assuming that you are speaking of a balanced three phase system where all three phases are120 electrical degrees apart, if current in one phase is missing then the resultant current in the neutral would be having a magnitude of almost9.9A (a little bit less than10).

hope I could shed some light onto your question.

Regards,

there is no current in the neutral because of the2 ph are share the total current and this is not possible because of fault current in phase 

10 amp