Power Distribution Equipment 249
POWER DISTRIBUTION INSIDE INDUSTRIAL
AND COMMERCIAL BUILDINGS
Electrical power is delivered to the location where it is to be used,
and then distributed within a building by the power distribution system.
Various types of circuit breakers and switchgear are employed for power
distribution. Another factor involved in power distribution is the distribu-
tion of electrical energy to the many types of loads that are connected to
the system. This part of the distribution system is concerned with the con-
ductors, feeder systems, branch circuits, grounding methods, and protective
and control equipment that is used.Raceways
Most electrical distribution to industrial and commercial loads is
through wires and cables contained in raceways. These raceways carry the
conductors, which carry the power to the various equipment throughout
a building. Copper conductors are ordinarily used for indoor power distri-
bution. The physical size of each conductor is dependent upon the current
rating of the branch circuit. Raceways may be large metal ducts or rigid
metal conduits. These raceways provide a compact and efficient method of
routing cables, wires, et cetera, throughout an industrial complex. A cable
tray raceway design for industrial applications is shown in Figure 9-4.Feeder Lines and Branch Circuits
The conductors that carry current to the electrical load devices in a
building are called feeders and branch circuits. Feeder lines supply power to
branches, which are connected to them. Primary feeder lines may be either
overhead or underground. Usually, overhead lines are preferred because
they permit flexibility for future expansion. Underground systems cost
more, but they help to maintain a more attractive environment. Secondary
feeders are connected to the primary feeder lines, to supply power to in-
dividual sections within the building. Either aluminum or copper feeder
lines may be used, depending on the specific power requirements. The
distribution is from the feeder lines, through individual protective equip-
ment, to branch circuits, which supply the various loads. Each branch cir-
cuit has various protective devices according to the needs of that particu-
lar branch. The overall feeder-branch system may be a very complex net-
work of switching equipment, transformers, conductors, and protective
equipment.