KVA Load-Carrying Capacity of Wire1
Table 1.
(2) Steel.
Steel wire used as a
weatherproof covering is not to be
conductor permits long spans because
considered as insulation, although it
of its high tensile strength.
Steel
does prevent breakdowns on the lower
has about 10 to 15 percent as much
primary voltages caused by conductors
conductivity size for size as copper,
swinging together.
For all primary
but
the
short
life
and
low
distribution over 5,000 volts, bare
conductivity of steel wire is overcome
conductors are ordinarily used.
to some extent by the use of copper-
clad steel made by welding a copper
(5) Secondary
distribution.
coating to the steel wire.
Weatherproof
wires
are
used
for
secondary
distribution.
The
(3) Weatherproofing.
Triple-
weatherproof covering is an effective
braid weatherproofing is preferred to
insulation
for
secondary
voltages,
double braid.
Improved types of
permitting rack-type distribution and
weatherproofing
include
plastic
closely spaced secondary conductors.
covering, and layers of impregnated
No wire smaller than a No. 8 is to be
unspun cotton or impregnated rubber
used for secondary distribution or for
filler.
Before these newer type
any external transmission of power.
coverings are used, approval should be
obtained
from
the
higher
command
b. Voltage
drop.
As
stated
having jurisdiction.
previously, a wire size is selected on
the basis of the allowable voltage
(4) Primary distribution.
For
drop and the load to be carried. The
primary
distribution
below
5,000
voltage drop is perhaps the more
volts, either bare or weatherproof
important criterion in that it causes
conductors may be used.
The ordinary
2-9
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