You're on the midnight shift when production stops because one of the four plant air compressors blew a fuse. Unfortunately, the correct 100A fuse isn't on site so you install an available 150A fuse. You note in the repair log that maintenance needs to replace this with the correct fuse later that day. Famous last words: What can possibly go wrong?

Assuming you found and corrected the fault, this risky situation may pass without incident. But what if another fault occurs on that phase, and the upstream feeder trips? What are the production losses then? Or what if the conductor, no longer protected by a 100A fuse, melts?

Temporary oversizing of overcurrent protection devices can save a company huge production losses. And pressure, along the lines of "do it or you're fired," is a bit hard to resist. Yet, it means a code violation even if temporarily.