One interesting difference between UL and IEC standards for fuses is that American UL standards often state a requirement for a fuse to withstand 100% or 110% rated current for a minimum of 4 hours. This means that the fuse is allowed to fail after 4 hours at its rated current.

In effect this means that when selecting a UL certified fuse you need to bear in mind that you should not continuously load it above around 75% capacity to ensure long term reliability. In contrast European IEC standards tend to require a fuse to withstand 100% rated current at room temperature indefinitely. This is one of those historical important points that is often unknown to engineers as they no longer tend to open up a fuse manufacturer catalog and see important information like this in the front, but instead search directly to fuse data sheets on the web where this 100% load issue is typically not made clear.