208Y/120-Volt System
The 208Y/120-Volt system is frequently used for small commercial businesses and in some network areas because it supplies 120-Volt single-phase for lighting and 208 Volt three-phase for small 200-Volt motors. It is not used very often in industry because a 480-Volt system is more economical for large motor loads.
480Y/277-Volt System
Since this system permits 277-Volt single-phase loads to be connected from the three line-to-neutral circuits, and 460-Volt three-phase motors to the three line wires, it fits in very well in both industrial plants and larger buildings. Fluorescent lighting and other single-phase devices have also been developed specifically for use with this system. The combination system provides overall savings of 40 to 45% when compared with a system using separate transformers for power and lighting. Any essential 120 Volt loads can be supplied from dry-type transformers with an overall savings of 25 to 30% in the investment.
208Y/120 Volt Versus 480Y/277 Volts
When compared with the 208Y/120-Volt system, the 480Y/277-Volt system has economic advantages not only from the standpoint of the savings in copper but also from service entrance switchgear and utilization equipment. The smaller current at 480 Volts for any given kVA of supply transformer capacity permits the use of protective devices with both smaller frame size and interrupting rating - both of these factors permitting significant savings.
Because a given conductor can carry more than twice the kVA load at 480 Volts than at 208 Volts, the savings for feeders of moderate length can be quite significant.
