an area is commercial, consisting of motors and other
three-phase equipment. The other type of circuit is
called the wye (Y) system (fig. 4-30) and is used
primarily for residential use.
Secondary circuits (secondary mains) are circuits
that originate from the secondary windings of a
distribution transformer and are 600 Vac or less. The
secondary circuits are also configured either delta (A)
(fig. 4-29) or wye (Y) (fig. 4-30) and are also used for
the same type of loading as the primary circuits.
Secondary circuits are either three phasemeaning
those with three live conductorsor single phase,
which can be one live conductor and a neutral or two
live conductors and a neutral.
A service drop is the combined conductors used to
provide an electrical connection between a secondary
distribution circuit and a user's facility. There are
different ways of installing the service drop. Some
typical secondary racks used to install service drops are
shown in figure 4-31. Whether using the racks with
individual conductors or self-supporting service cable,
known as triplex or quadraplex, to provide a service
drop, you must maintain a minimum aboveground
distance. Aclearance of 12 feet over lawns or walkways
accessible to pedestrians and 18 feet over roads or
alleyways subject to truck traffic as recommended by
the NEC©, as shown in figure 4-32. When the nearest
distribution pole is over 125 feet from the facility to be
connected, an intermediate support pole must be
CONTROL AND PROTECTIVE
A power distribution circuit, like any other
electrical circuit, requires the use of special devices to
provide control and to protect the system from internal
or external influences that may damage the circuit.
A distribution cutout provides a high-voltage
mounting for the fuse element used to protect the
distribution system or the equipment connected to it.
Figure 4-30.Three-phase wye (Y) primary and secondary system.