Inrush peak for 50/60Hz transformers mostly from magnetizing current -> core saturation and residual flux, and of course input V. As the saturation curve does not extend past the pi/2 inrush peak, any further inrush past a few mSec is typically from filling up the coulomb buckets on the secondary side. This is a tau-based thing, so both DCR and Z would be used to determine the current-interrupt component's expected I2T. Inrush for the 'small' transformer is being discussed can have peak inrush well over 20x rated continuous. For the smaller industrial control stuff under 5kVA, series thermistor in lieu of fuse is common where wire and breaker are correctly sized.
The AHJ's focus should be on SCCR, which is inversely proportional to the DCR of the secondary windings, and coordination between the distribution breaker and the fuse. Perhaps you can distract the assessment person with a Bugs Bunny or Daffy Duck cartoon on your pad/laptop. Brian - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
