Power Distribution Of Small Office Building

Power Distribution Of Small Office Building

 A small office building, for example, might require 120 volts for interior lighting and receptacles and 208 volts for heating, air  conditioning, and exterior lighting. In this example, the utility company supplies 208/120 volt, three-phase, four-wire service.

The main incoming line is divided into four feeders. The two outer feeders supply power directly to the 208 volt heating and air conditioning units. The two inner feeders are divided into a number of branch circuits. One set of branch circuits supplies power to exterior lighting. The second set of branch circuits supplies power to interior lighting and receptacles

The electric utility uses a step-down transformer to supply power to a facility. There are a number of ways the secondary of the utility transformer could be configured. In the following example, the utility supplies power from a transformer with a wyes-connected secondary. The secondary winding of the transformer produces 208/120 VAC. Single-phase 120 VAC is available between any phase wire and neutral. Single-phase 208   VAC is available between any two phases. All three phases are connected to any equipment requiring three-phase power..

Incoming power is metered by the utility company. In this example, power is supplied to the building through a main service disconnect. A switchboard divides the power into four feeders for distribution throughout the building.