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Single Phase Transformer bolted fault

Single Phase Transformer bolted fault

Single Phase Transformer bolted fault

(OP)
I'm looking at several different fault current tables for single phase XFRs and I see several different values for similar sizes and %Z.  Three phase calcs seem straight forward (i.e. 3P bolted fault for a 500kVA 277/480 5%Z is about 12,028 amps).  I have a table in front of me saying that a 1P XFR 15kVA 120/240 1.6%Z is 5456 amps L-G fault...My calculation shows to be 7813 Amps...I've seen table that show my calculation to be right as well....
WHAT AM I MISSING HERE?

Thanks in advance.

RE: Single Phase Transformer bolted fault

A three-wire 120/240 V single-phase transformer is not a straightforward fault calculation.  120 V impedance is different than 240 V impedance, but not in a simple way.  

I believe there was a fairly involved discussion on this here a couple of years ago.  

Conrad St. Pierre's book on Fault Calculations has a lengthy explanation.   

RE: Single Phase Transformer bolted fault

Don't forget, for a 1 phase transformer, you must consider the length of the cable for the return of the current to the transformer.

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