Electronic – Is this fuse time-current curve wrong


I'm looking at the datasheet for the Bel 0ADKC /0ADKP fuses.

In it is this:
enter image description here

These curves don't seem correct. Notice that the curves for fuses with >= 800mA asymptotically approaches a value that doesn't match their rated current.

Is there some assumption I am unaware of? Or is this graph in error?

This isn't the case with other curves that I see, but those were fast-acting fuses and these are time-delay fuses.

For comparison these are the curves for the fast-acting Bel 0DAC/0ADAP fuses and the curves do approach the rated current.
enter image description here

Best Answer

They don't match the blow current. The graphs are the current that the fuses blow at (not the rating with one number). The reason for this being is it takes temperature to blow the fuses and then the fuse material must break down. This process does not happen instantaneously, its a phase change process. So the longer you dwell above the temperature, the more it will break down. If the current is exactly at the point of breakdown, it could take a long time to break down the fuse material down.

To really blow a fuse, you must go beyond the blow current, the more you go beyond the blow current, the faster it will blow.

It's also why currents close to the blow current should not be approached for long periods of time (like between 700mA and 800mA) as the curve probably also extends to this region but was not tested.