Quantcast Chapter 4. Overhead Distribution

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TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
4-1. Relevant overhead distribution guid-
the United States, permission must be obtained
from the nearest District Office of the U.S. Army
Corps of Engineers. When crossings are made in
Maintenance work involving aerial line changes re-
waterways under the jurisdiction of other authori-
quires an understanding of the basic design pre-
ties, those authorities should be consulted.
mises of overhead construction requirements.
b. Identification requirements. Poles, towers, and
a. Location of electric circuits on poles. Where
other supporting structures should be marked or
more than one electric circuit is carried on a pole,
numbered to facilitate identification by employees
the highest voltage is at the top down to the lowest
voltage above any communication circuits. Through
authorized to work on them. If the facility has no
wires of the same voltage level should be carried
consistent identification method, it is recommended
above local wires (those which are tapped fre-
that such a system be implemented.
quently). The two or more wires of a circuit should
c. Climbing space. Despite the fact that, where
always be carried in adjacent positions. To facilitate
practicable, nearly all pole work will be done from a
troubleshooting, wires of a circuit should always
bucket, the need for climbing space still exists. Suf-
take the same positions on all poles, except where
ficient space must be reserved for positioning the
long lines have been provided with a transposition
bucket to enable the linemen to perform their tasks;
(change of line positions) to reduce electrostatic and
and actual climbing may be required on occasions.
electromagnetic unbalance.
The recommended facility climbing space require-
b. Joint electric supply and communications cir-
ment is a square 30 inches (750 millimeters) on
cuits on poles. Electrical supply wires must be car-
each side. Figures 4-l and 4-2 show details for
ried above communication circuits. Minimum clear-
various conditions. Any maintenance, repairs, re-
ances between supply wires and communication
placement, or addition must be done in a way that
wires are specified in the NESC.
maintains at least the minimum climbing space re-
4-2. General construction guidance.
quired by the NESC which may be less than the
recommended space.
Rights-of-way for navigable water crossings and
d. Obstructions. Poles and other structures
structure identification and climbing space free of
should be kept free from posters, banners, nails,
obstructions must meet the following requirements.
radio antennas, signs, or other devices that might
a. Rights-of-way requirements. When the system
interfere with safe working conditions.
is being extended across navigable waters within
4-3. Voltage terminology.
mission system is used for high and ultra-high volt-
age systems; subtransmission system for 46- to 69-
Voltage terminology can be very confusing, espe-
kilovolt systems; and distribution system is used for
cially if there is no mutual understanding as to
35 kilovolt down to and including low-voltage sys-
whether the term is defining a voltage level, a de-
tems. Utilization voltage is also used to describe the
livery usage, or an origination point.
voltage from which the equipment directly operates,
4-4. Voltage level classification.
which may in some cases be a medium-voltage in-
The accepted standard for voltage classifications is
ANSI/IEEE 141. Low voltage is used for 600 volts or
4-6. Voltage origination point.
less, medium voltage is used for above 600 volts to
Input to a device which transforms voltage from one
69,000 volts, high voltage is used for 115 to 230
level to another is called a primary circuit, while the
kilovolts. Any voltage above this is called ultra-high
voltage. The term high voltage is most often used
device's output is called a secondary circuit. While
when medium voltage is meant.
most transformers are used to step down voltages,
there are cases of step-up systems; so a primary
4-5. Voltage delivery usage.
circuit could have a lower voltage than a secondary
There is no standard for delivery usage; but trans-


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