SKM 208V calculated sc current too low. Any ideas?

[julesm]

Hello and help.
My sc report results don't make sense. I have a 3000A 480/277V building with utiltiy reporting 51k AIC. For some reason all the 208V fault currents are calcuulated in the 500A range. When I model the 208 v portion separately, the results are in the 5000A range. Any ideas whate my glitch is??? Thanks!

 

[davidbeach]

Garbage in, garbage out? What size transformer do you have between the 480 and the 208? What is the transformer impedance? I haven't regularly used SKM for the past 3 years and not at all for the past 1.5, but up until 3 years ago I used it extensively and GIGO always turned out to be the explanation for weird results in routine calculations.

 

[julesm]

Looks like some glitch -
If I first add a new 208V bus, the Isc is reasonable -5k ish. When I rerun, it drops to .5 ish. Hmmm
Can't revert.

 

[davidbeach]

Send it to SKM, they've always been helpful.

 

[nightfox1925]

Just curious. What is your transformer capacity, KVA? Your transformer impedance? I assume that you are having a 480-208Y/120V step down transformer and you intend to calculate the 3Phase 208VAC short circuit current.

 

[julesm]

OK I had a corrupted SKM project... I "merged" the existing project into a "blank" one and the new results look great! thanks for the advice. This actually got me revisisting transformer technology and conceps which should happen every once in a while! (There are some interesting transformer discussions this site.)
Thanks to all for ideas ans advice.
Best,