I somewhat often run into custom control panels with multiple power sources. I am curious how everyone else handles this. For example, I often see custom panels with multiple 480VAC inputs, each separate from one another.

Do you analyze each circuit independently and then label the enclosure with the worst case IE? Or do you model both terminating onto a single bus (representing the panel)?

While these circuits are separate from one another let's assume we can not rule out propagation if an arcing fault occurs with one of the circuits. By modeling both circuits connected to one bus does the result represent an actual overall IE or is this fictious?

Maybe one day scenarios like this will be covered by IEEE 1584.

I don't think it is possible to model them accurately. Those panels often contain multiple terminal blocks, relays, starters, taps upon taps of varying wire sizes, control transformers, fuse blocks, a wide range of bus gaps and more variables.

I've mentioned on here before I spent a couple years doing forensic work, investigating electrical failures. I had a few cases involving control panels. One I've specifically mentioned was caught on security camera. It had current limiting fuses upstream but they did not clear. The panel was a fireball long enough for an employee to approach the panel once he noticed, decide that was a bad idea then run to kill the upstream disconnect. I don't remember how long that took but it was several seconds to say the least. The IE was probably in the hundreds of calories or more due to duration. I modeled this one and the fuses should have cleared very quickly resulting in a very low IE.

To answer your question, about all you can do is run the calcs to the line side of the control panel and note in the report that it is just an estimate and actual IE level is unpredictable. Either that or model to the line side which should have the highest fault current and fail the protective device so the 2 second rule kicks in.

bbaumer I appreciate your experience with this. I like to assess each point especially if we step down voltages at the panel and labeling based on the worst-case of the points analyzed. Based on your thoughts I now kind of like the idea of expanding on this and making all points at the cabinet omit OCPD's and use the 2-second rule and then noting the uncertainty with the analysis and equipment of this type.