Figure 3-24. Line symbols for electric power distribution.
temperature is lower, add 3 percent for each 5
connected to the system. The demand load is the
degrees F; if higher, subtract 2 percent for each 5
maximum amount of power which may be expected
degrees F. You will generally find that unit electrical
to be required at one time. Note that the demand load
power devices have pertinent wiring and hook-up
is less than the connected load for some services
diagrams on the name plate or other prominent place.
because not all units would be operated at one time,
and the overall demand is less than the sum of the
individual demand loads because the peak demand
3-19. ELECTRICAL DISTRIBUTION
would not occur on all services at the same time.
PLAN
a. Figure 3-26 shows the electric distribution
b. In addition to the layout plans, detail
information normally provided on the utility plan for
drawings are used to show complex installations,
a small installation. The letter in circle at each
standard connection methods, and specifications. On
building A B or C ) indicates the phase or phases
figure 3-26, note that the number and size is specified
to be connected to the building. Figure 3-27 is a
for wiring on some spans (as 4-#6, for example), the
pictorial view of the installation. You can see that
number of wires is indicated by cross lines on the
only the total connected load need be listed for an
service drops (as to building number 3), and no
installation this small. The utility layout for a larger
specification is given on some spans (such as those to
installation would provide you with a more detailed
building number 4). A note on the drawing will
tabulation of electrical loads for each load center as
normally specify the minimum wire size that can be
shown in figure 3-28. The tabulation shown is for the
used for those not specified. As shown in figure 3-
hospital layout shown in figure 3-2. The connected
24, two wires are used unless a larger number is de-
load is the total power requirement of all the items
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