But, that doesnât mean students have to take them all in the same week. Our class structure allows us to provide 5 cycles of classes for every 30-day period. As long as students take the classes in order, (Class 1, Class 2, Class 3, Class 4), they are free to switch between any of the cycles for that 30-day period. The only other requirement is that all 4 classes must be completed within 30 days of the first class.
Re: Advantages of three phase systems over single phase. The big advantage with 3 phase mains is that any electric motor connected to it is more efficient, has smother running and uses less parts so is more reliable. There is also a slight advantage in using 3 phase transformers over single phase ones.
Before going into the details of why the neutral must be used, I'll explain how the system works in a three phase, four wire system. Three phase four wire system:(3 phases and 1 neutral): The distribution substation has a delta-star transformer if the transmission system was in delta, which it usually is. The delta system is converted to a star system, and the neutral point is used to lay another line, which is called the neutral line.