I am by no means that knowledgable about bridge cranes. However I did run into a situation like this just recently. This crane was a 480v 3 phase that used 2 shoes per line. The feeding cable from the shoes was only a #10. The wire had melted off and became brittle in other spots on the one phase. To make a long story short, I felt as if the wire was too small to handle the load. We replaced the #10 with a #6. (The bridge crane was protected with a 40A disconnect.) Oversized the wire for added comfort. The problem actually arose from the individual shoes and tracks being overly dirty and carbonized. Causing spiking currents to "pulse" through the wiring. After a good cleaning and new shoes the problem was fixed and the current was found to be well within the range of the #6 we installed. Hope this maybe helps.
