Investigating Fuses: Understanding Why Fuses Melt

[O_oSam]

I have just started a Physics project which I have already missed the deadline for >_<

I have a very minimal set of results, I basically took a power supply>smoothing unit and put them in a circuit with a component holder and two resistors (in parrallel so I didnt blow the ammeter) and took readings.

Was wondering if I could get some helpful information etc. on fuses. Can anyone give me a detailed explanation of why fuses melt, I was hoping to tie in Electrical resistivity [I'm aware it changes as fuse heats] and possible thermal conductivity?

Does the thermal expansion of a wire have any relevance?


Thanks

Sam

 

[BigJDubs]

Fuses are designed to protect electrical circuits from excessive current. When too much current passes through a fuse, it will heat up and eventually melt. The melting point of the fuse depends on its material composition, but is typically around 125-150°C. This melting point is lower than the temperature at which most electrical components would be damaged by an overcurrent, so it acts as a protective device.The electrical resistivity of the fuse material increases with temperature, meaning that the resistance of the fuse also increases with temperature. As the resistance of the fuse increases, the current flowing through it decreases, thus limiting the amount of heat generated by the fuse. Thermal conductivity becomes important as the fuse heats up, because it determines how quickly the heat energy is transferred away from the fuse. If the thermal conductivity is too low, then the heat energy will build up more quickly and cause the fuse to melt faster. The thermal expansion of the wire also affects the fuse's performance, as the wire itself will expand when it gets hot and this can affect the contact between the wire and the fuse.