252 Electrical Power Systems Technology
voltage, current, and/or frequency. It is also necessary to ground the
power system at the service entrance location. This is done by a ground-
ing electrode, which is a metal rod driven deep into the ground. The
grounding conductor is attached securely to this grounding electrode.
Then, the grounding conductor is used to make contact with all neutral
conductors and safety grounds of the system.
SERVICE ENTRANCE TERMINOLOGY
There are several terms associated with service entrance equip-
ment. The service entrance conductors are a set of conductors brought to a
building by the local electrical utility company. These conductors must
be capable of carrying all of the electrical current that is to be deliv-
ered to the various loads inside the building that are to be supplied with
power by the power system. Conductors that extend from the service
entrance to a power distribution panel or other type of overcurrent pro-
tective equipment, are called feeders. Feeders are power lines that sup-
ply branch circuits. A branch circuit is defined as conductors that extend
beyond the last overcurrent protective equipment of the power system.
Usually, each branch circuit delivers electrical power to a small percent-
age of the total load of the main power system.
In commercial and industrial installations, switchboards and panel-
boards are used to supply power to various loads throughout the power
system. A switchboard is a large enclosure that has several overcurrent
protective devices (fuses or circuit breakers). Each feeder is connected
to the proper type of overcurrent device. Often, switchboards contain
metering equipment for the power system. Panelboards are smaller than
switchboards, but are used for a similar purpose. They are enclosures for
overcurrent devices for either branch circuits or feeder circuits. A com-
mon example of a panelboard is the main power-distribution panel that
houses the circuit breakers used for the branch circuits of a home. For
more specific definitions of terms, you should refer to the most recent
edition of the NEC.
Power Distribution System Components
Several specialized types of power distribution system components
are available today and should be reviewed.