efficiency, and may damage motors when
allowable voltage drop for a circuit
As defined, voltage drop
is known to be 3 percent. The demand
is the difference in voltage between
load is 20 KVA and the length of the
the input and output ends of a
circuit is 450 feet.
The circuit is
It is caused by
3 4W 127/220 volt type. Using figure
9, determine the smallest permissible
known as "line loss." The percentage
wire size and the resulting voltage
of line loss or voltage drop may be
expressed as either a percentage of
the voltage required at the receiving
Solution: Figure 9 is used because it
end or as a percentage of the voltage
is based on the proposed 3 4W 127/220
impressed or generated by the source
to the line.
For example, figure 6
required wire size enter the demand
shows the voltage at the motor to be
load of 20 KVA on the upper horizontal
scale and follow vertically downward
Therefore, the line loss
to the intersection with the diagonal
of voltage drop is 11 volts.
line representing 3 percent voltage
voltage drop expressed as a percentage
drop pertaining to the upper KVA
of the voltage at the receiving end is
Project from this point of
intersection a horizontal line to the
right until intersection is made with
the vertical line representing 450
This second point
In civilian practice, the percent
of intersection falls between the
voltage drop is usually taken as a
curves for wire sizes No. 2 and No.
percentage of the voltage required at
In such a case, select the
the receiving apparatus.
practice, the percent voltage drop is
determine the actual voltage drop
taken as a percentage of the voltage
using the 1/0 wire, enter 450 feet on
at the generator.
For typical TO
the bottom scale; follow upwards to
installations, the voltage drop is
usually kept within a 5 percent limit
follow horizontally to the vertical
line representing 20 KVA as read from
Figures 7, 8, and 9
the upper horizontal scale.
will be used in this course for
point, the voltage drop is read as 2.4
percent. From table 1 it can be seen
that a 1/0 wire is capable of carrying
which correlate the several factors
the 20 KVA load and from the above
Their use is discussed in
procedure, the voltage drop is under
the following examples.
the 3 percent specification.
Line voltage drop.