The software I use has a default inrush factor of 12. I have always used this default inrush factor for all my studies I have done. Recently I was told that the factor of 12 is not acceptable and that I should be using something more in the 6-8 range. Can anyone shine some light on this for me?

6-8 is certainly on the low end. I have always used the following (based on my Square D upbringing )

Liquid Filled or Unknown Transformer = 12X
Dry Type = 10X
Cast Coil = 8X

However the actual inrush is also dependent on factors such as when in the voltage waveform the circuit is closed, past magnetizing history etc. so it is possible to have a lower inrush just based on these variables but the numbers above are what I use.

Thanks for the reply. This helps!

Be aware that it's not uncommon for new energy efficient dry type transformers (15-500 kVA) to have inrush factors in the 15-20 range.

When purchasing a new transformer, ask the manufacturer for the specific information.

When analyzing an existing facility, 12 is a good assumption. If there were actual inrush problems, it would be apparent and someone would be making some noise about it. I wouldn't recommend pointing out inrush problems according to the software in an existing facility where there are no real life inrush problems.