disconnecting the service conductors from the supply
source. It may consist of a single manually operated
switch or a circuit breaker. The NEC
minimum size for entrance switches at 60 A for the
fuse type and 50A for the circuit breaker type. A
CIRCUIT BREAKER is a protective device that
automatically opens the circuit, rather than burning
out like a fuse, when the amperage exceeds that rated
for the circuit breaker. The NEC
minimum size of 100-A service for individual
residences. However, when not more than two two-
wire branch circuits are installed, a 30-A entrance
switch may be used.
A PANELBOARD (fig. 9-10) is defined by the
as a single panel, or a group of panel units
designated for assembly in the form of a single panel,
including buses. It comes with or without switches
and/or automatic overcurrent protective devices for
the control of light, heat, or power circuits of small
individual as well as aggregate capacity; it is
designed to be placed in a cabinet or a cutout box and
placed in or against a wall or partition and is only
accessible from the front.
A BREAKER PANEL uses a thermal unit built
into the switch with the breaker being preset at the
factory to open automatically at a predetermined
Figure 9-11.-Lighting panel.
ampere setting. It maybe reset to the ON position
after a short cooling-off period.
LIGHTING PANELS (fig. 9-11) are normally
equipped with 15-A single-pole automatic circuit
breakers, while the power panels may have one-,
two-, or three-pole automatic circuit breakers with a
capacity to handle the designated load. In most
buildings, the entrance switch and panelboards can
be mounted close to each other; however, they must
be placed where service and maintenance can be
easily performed. They should not block any passage
that is supposed to be open, and they should not be in
a place where exposure to corrosive fumes and
dampness is imminent. Panelboards should be located
as near as possible to the center of the electrical load.
ELECTRICAL CONDUCTORS generally consist
of drawn copper or aluminum formed into wire. They
provide paths for the flow of electrical current.
Conductors are usually covered with insulating
materials (fig. 9-12) to minimize the
Figure 9-12.-Types of single insulated