Help with solving short-circuit current

[Sparky Bill PE]

To solve for short circuit current, do you just know you're supposed to take the phase voltage instead of the line voltage? Since the system was in 3-phase I wouldn't have thought to change. 

 

[DLD PE]

Yes.  Since impedence is always a "per phase" quantity, you need to use phase voltage when solving for the current.  If you were given that this was a delta source, you could assume the line voltage=phase voltage, but the problem doesn't state this, so you must assume line voltage and convert to phase. 

 

[akyip]

What DuranDuran said.

Basically, short-circuit current or fault current is a line current quantity. So typically you use the line-to-neutral voltage phasor and divide that by the total impedance between the source and the fault location to obtain the fault current (line-current) phasor value.