在美国，208Y/120伏系统的大部分容量存在于城市高密度商业区的地下二次网络中。这种分配系统的使用非常广泛，而且在未来的许多年里可能会继续如此。一些公用事业公司还为二级网络区域以外的大型孤立商业负荷提供208Y/120伏服务，如购物中心和学校。50多年前，我们今天熟悉的第一个自动空调网络系统于1922年在纽约市投入运行。 当时的电压水平是199Y/115伏。该网络系统是在需要高度可靠的电力服务、灵活性和经济性来服务电力和照明负载的情况下诞生的。很自然，它最早的应用是在大城市的商业部门，取代了爱迪生的三线d-c网络，后者变得笨重且不经济。二级网络的使用迅速增加。如今，该国约90%的人口在10万或以上的城市，以及约1/3的人口在2.5万至10万之间的城市，都在使用它。 对1924年发表的一些AlEE论文的研究表明，选择四线199Y/115伏系统的基本原理是允许向当时可用的标准单相和三相利用设备提供服务。主要负载部件是115伏白炽灯和220伏三相电动机。网络系统的电气“刚度”导致220伏电机的性能普遍可接受，而对于199Y/115伏径向系统来说，这不一定是真的。 本文回顾了自20世纪20年代初以来，与标准C84相关的电压水平变化。1预计日期为1976年。引文:德克萨斯州达拉斯ASHRAE交易会第82卷第1部分研讨会

Most of the 208Y/120-volt system capacity in the U. S. is found in underground secondary networks supplying high-density commercial areas of cities. The use of this type of distribution system is very extensive and probably will continue to be so for many years to come. Some utilities also provide 208Y/120-volt service to large isolated commercial loads outside of secondary network areas, such as shopping centers and schools.The first automatic a-c network system as we are familiar with it today was put into operation in New York City in 1922 more than 50 yr ago. At that time the voltage level was 199Y/115-volts. The network system had its inception under circumstances requiring highly dependable electric service, flexibility, and economy to serve a mixture of power and lighting loads. It was natural that its earliest applications were in the business sections of large cities supplanting the 3-wire, Edison d-c networks which had become unwieldy and uneconomical. The increased use of the secondary network was rapid. Today it is used in about 90% of the cities in the country having a population of 100,000 or more and in about 1/3 of all cities with a population between 25,000 and 100,000.A study of some of the AlEE papers presented in 1924 reveals that a basic part of the philosophy in selecting the four-wire, 199Y/115-volt system was to permit the supply of service to standard single-phase and three-phase utilization equipment available at that time. Principal load components were 115-volt incandescent lighting and 220-volt, three-phase motors. The electrical "stiffness" of the network system resulted in generally acceptable performance of the 220-volt motors, whereas this would not necessarily be true for 199Y/115-volt radial systems.This paper reviews the changes in voltage levels since the early 1920s as relates to standard C84.1 which was expected to be dated in 1976.