Do Fuses have a Half Life?

Just draw too much current and their life is over. The life span is entirely up to you. Used correctly with no spiking, overloads, etc they'll last indefinitely depending on the type of fuse you're referring too.

The life of a fuse can also be terminated by a building inspector - or insurance company - who would rather have the homeowner use breakers! All joking aside, I've seen working glass fuses in the electrical boxes of old farmhouses in New England. It's remarkable that these fuses still work, but - used properly - they live on.

Actually, some fuses do eventually fail at less than rated current, and the closer you get to the rating, the sooner they fail. This is unusual, however, and falls into the category of manufacturing defect.

All fuses "age". The more energise/de-energise cycles they go through and the nearer their rating they are used, the shorter the life. As it is a piece of 'rated' wire, the more you stress it electrically, the more likley it will blow on the next current increase.

Motor circuit protecting fuses certainly do, as the motor "in rush current", which is many times that of normal operating full load current, and certainly quite a bit more than the 25% over full load current you are probably fused for, eventually takes its toll. It will take years for this damage to manifest itself, but it eventually does. (fuse manufacturers will say bull to this, but in the real world of plant maintenance, you see this happen) Some heaters will also do this sort of damage, as the load is almost purely inductive leading to the large in rush currents.

Sorry to be picky, but heaters are usually mostly resistive (unless the have a fan) - the initial current is higher due to the lower resistance of the element at lower temperatures.

Merriam-Webster says:

Main Entry: half-life
Pronunciation: -"lIf
Function: noun
1 : the time required for half of something to undergo a process: as a : the time required for half of the atoms of a radioactive substance to become disintegrated b : the time required for half the amount of a substance (as a drug, radioactive tracer, or pesticide) in or introduced into a living system or ecosystem to be eliminated or disintegrated by natural processes
2 : a period of usefulness or popularity preceding decline or obsolescence

In the sense of #1, I would say NO, because you cannot divide a fuse as a material, where half of it undergoes a change and the other half remains. In the second sense, we might think of a fuse as having a period of usefulness, however, when it's usefulness is over it does not go into decline or obsolescence, it must be immediately replaced. Therefore, I would say that a fuse does not have a "half-life".

Now on the other hand, does it have a "life", that is a Mean Time Between Failure (MTBF)? MTBF is a measurement often given to manufactured objects (especially electrical or mechanical components) based on statistical data, measuring the life-time (often in terms of cycles rather than time units) of that component under strictly controlled conditions. If the fuse manufacturers have tested their components under some extreme condition, they may very well give a MTBF rating, but my bet is they don't. Normally, unders typical operating conditions, fuses are very long-lived, as noted above, so it would be silly to test in that manner. Fuse life-time is usually cut short by unexpected events, like current overloads, abnormal cycling, etc.

Never heard of this. LEDs do about 40 years.