Yes, you need to know the transformer rating, transformer impedance and line impedance to figure out the fault current. At higher currents, the transmission cables (especially the poco ones that are undersized by NEC standards) act as resistors, further limiting the fault.
The transformers themselves are stupid- they don't know a fault from a load until they burn up. The fuse on the primary is only slightly smarter, but apparently not quite smart enough in this instance...
[This message has been edited by SteveFehr (edited 11-30-2006).]
