What software program or what is the recommended way to calculate fault current? Every program I use to calculate fault current has a different answer. Thanks for the replies.

Make sure the circuit/equipment configuration is the same and check them with hand calcs.

I did check with a hand calculation. Results vary from a couple hundred amps or a little more. Am I being to critical? Should I use MVA, Ohmic, and include X/R ratios? How about the methods published by Bussman? Bussman has a free program to calculate fault currents. Can this method be trusted?

When you input basic info to a vendor program, that calc is made based on the developer's assumptions, but when you hand calc with specific x/r and sequence impedances, you get a more accurate result. If you are talking about the difference of say....20,000 amps or 20,200, what's the difference? I would say yes, that's a bit picky.

We are not that good anyway!

The key is to gather all available data, make any assumptions necessary, and understand the impact those assumptions may have on your results.

I normally use the per unit method and actual x/r ratios.

Thanks for the reply. You answered my questions.