Electrical loads can be classified according to its importance as; normal loads, important loads & emergency loads. Normal loads are the loads from which the power can be switched off for a period of time; this period may be short or long depending on the case itself. Important loads are the loads which can be switched off for a very short time. Emergency loads are the loads which cannot be switched off at all such as hospitals. Normal and emergency loads are out of the scope but important loads will be discussed in some details. Important loads are usually supplied using two sources of power. The two sources are usually the transformer of the utility and a stand by generator used in case of the power of transformer is gone. If the main power has been activated again, the generator will be switched off and the load will be supplied from the transformer. This process is organized and performed using a device (Circuit) called Automatic Transfer Switch (ATS).