The North American Grid can be defined as the entire interconnected system of electric apparatus, such as transmission lines, transformers, breakers, bus bars, capacitor banks, and inductor banks,  that enable the transportation of electrical power from its generating sources, namely electric power generating plants, to its points of consuptions, namely residential, industrial and institutional customers.  The North American Grid consists of four Interconnections which are interconnected via DC ties as shown in the diagram below. The DC ties make possible for each interconnection to operator asynchronously from the others.