Most of what you need to know about fuses and how they work can be learned in the 1983 holiday classic, A Christmas Story. Just one look at that outlet overloaded with about 37 power cords coming into it has taught us all the valuable lesson that too much is just too much.
The difference is that most of us will probably never be able to change a fuse quite as quickly as Mr. Parker. Is it because he has that deep of an understanding about what fuses really do? Judging by his decision to add yet another cord to the mix, probably not. But we can take his example to the next level to gain a better understanding about a fuse's purpose.
Pardon the Interruption, By Definition
If you look at the raw definition of what a fuse is, you'll learn that it's a device that can interrupt the flow of electrical current when it's overloaded. But then again, that's like explaining that the function of the Hoover Dam is to interrupt the flow of water. When there's too much water, it goes over the spillway, blah, blah... you get the picture. It's about the same concept with a fuse, only replacing the water with electricity.
A Voltage and Amperage Manager
If you think it's a drag having your boss constantly telling you what to do and how to do it, you should be glad you're not a toaster. A toaster is a fairly simple device, and all it needs is the right amount of electricity to work (aside from all the components being connected and in good working condition, but that's a different lesson).
Knowing that a particular amount of electricity is needed for the toaster to work, the fuse is there to make sure that just the right amount of electric current is making its way to the outlet where the toaster is plugged in. Too little electricity, and the heating coils wouldn't even be able to get hot-too much and the toaster itself would be toast. The fuse isn't necessarily limiting the amount of electricity, but it keeps the flow just right.
What If the Dam Breaks?
Let's consider the above Hoover Dam analogy, only in electrical terms. There is something called a power surge, which happens when too much electric current is allowed through the power cables and your home and all the electrical devices get overloaded. Ever see all the lights in your house waver in and out but don't shut down completely? Yup, that was a power surge, alright.
Now, if the Hoover Dam experienced this kind of overload with water, it could break and there would be no way to stop the massive amount of water from bursting down the valley. However, when this happens with electricity, a fuse is designed to "blow" or "trip" and shut the flow of electricity off completely. In this sense, a fuse is providing protection, which prevents wires from melting, electric circuits in appliances from getting fried, and so on.
Fuses Here, Fuses There, Fuses Everywhere
It's virtually impossible to go a single day without encountering at least ten items that use electricity. And you guessed it; every single one of them has a fuse, or two or three. Lawnmowers, hair dryers, blenders, televisions, Christmas lights... you name it, there's a fuse in it. Fuses are protecting electric devices everywhere. But more importantly, the fuses are there to protect us. Thanks for the lesson, Mr. Parker.