Fuse Blowing

[morphuk1]

Hi
could somebody tell me why a fuse will blow if a live wire shorts to earth?

i understand that a fuse will blow when an appliance draws more than a rated current and i also understand that if a live wire comes in contact with a metal case and (providing its earthed properly) will go to earth but i dont understand why the fuse would blow when the live shorts to earth, i think i heard something that said that because the resistance decreases (because of the shorter path to earth) the current increases and blows the fuse therefore protecting the appliance and flex from overheating but im not sure if reduced resistance increases the current in the live wire.

could somebody clear this up for me

many thanks in advance

 

[Spark123]

(In a TN system) the fuse blows as the earth wire is connected to the same point as the neutral at the supply transformer hence when a phase wire touches the earth wire it is in effect a short circuit.