TABLE OF CONTENTS Selection of the principal secondary utilization voltage is critical and should be made early in the preliminary design stage of a project. This is a critical decision because it has a significant impact on the cost of the distribution system, distribution equipment, and energy efficiency. The considerations are the same whether new service and distribution systems for a new building are to be considered or a renovation or addition to an existing building is considered. The options in the case of the latter, however, generally offer more limited choices.
The most prevalent secondary distribution voltage in commercial and institutional buildings today is 480Y/277 V, with a solidly grounded neutral. It is also a very common voltage in industrial plants and even in some high-rise, centrally air-conditioned and electrically heated residential buildings, because of the large loads.
The choice between 208Y/120-V and 480Y/277-V secondary distribution for commercial and institutional buildings depends on several factors. The most important of these are size and types of loads and the length of feeders. In general, large motor and fluorescent lighting loads, and long feeders, will tend to make the higher voltages, such as 480Y/ 277 V, more economical. Very large loads and long runs would indicate the use of medium-voltage distribution and load center unit substations close to the loads. Conversely, small loads, short runs, and a high percentage of incandescent lighting would favor lower utilization voltages such as 208Y/120V.
The principal advantages of using higher...
