I am curious how others handle multiple circuits which exist in the same enclosure. Occasionally I run into custom built motor control panels which have 3-phase, 480VAC circuits which originate from different sources enter an enclosure and terminate onto different devices. My first thought is to analyze both hazard and to label the panel with the worst case. I may be over thinking this but what if one of these circuits arcs and eventually extinguishes but at some point this initiates the arcing of the second circuit. What is the effect of this increased arcing time if we are to consider both arcs occurring in series?

Hadn't really thought about that before. Similar to a transfer switch with two utility sources hot all the time.