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..
