Every electrical installation in a house or commercial building has main a breaker. It will shut off ALL electrical flow. Then, downstream, there will be a set of breakers covering smaller circuits, for example: dryer, range, water heater, heat, and several circuits for lights. All breakers are also overload switches, that is their job.
In the good old days we used fuses, that you had to unscrew and replace

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Note added at 3 hrs (2010-02-24 16:50:44 GMT)
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In the US, the main breakers are often simply referred to as "the mains". These are of course also switches, and if any work is to be done on the electrical system, a prudent electrician will manually shut off the breakers. Breakers work by shutting off, or breaking, the flow of current, in the event of an overload. They overheat, and a bimetallic trigger releases a spring loaded contact. They can then be reset when the problem has been identified and corrected. Reset is accomplished by pushing the breaker lever all the way to one side, and then again closing the circuit. It is a type of fuse, but old fashioned fuses would break by actually melting a strip of metal. They they had to be replaced. Modern breakers can be reset over and over.
In Denmark almost all domestic installation are three phase, 380 volts (I may be a bit off on the voltage, it has been a long time), and the circuits divide into 220 volts for most loads, but remain at the higher voltage for heavy loads such as clothes dryers. In the US most domestic installation are single phase 220 volt, which is branched off to 110 volt for most loads, but remains at 220 volt for dryers or heating plants.