The power distribution box is the center point of the zone distribution grid. Models are currently available in heights as low as 1-3/4". This is the conversion point between hard wiring done by the onsite electrical contractor and the premanufactured wiring system. Optimal efficiency is typically obtained by placing the power distribution box on a 20'-25' grid. Of course this only a starting point, as the boxes can placed to accommodate any situation. Circuit capacity ranges from four to eight circuits using a shared neutral - eight wire system or from three to six circuits using an independent neutral - eight wire system. Circuit density will depend upon individual needs as determined by the electrical engineer.