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What's on a Utility Pole?
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- Static Wire
The static wire is the pole's top wire which bleeds lightning surges off the power
lines during a storm. Without a static wire, lightning induced voltage would otherwise
build up on power line conductors during a lightning strike and cause damage. The
static wire is connected to the grounding conductor.
- Grounding Conductor
The grounding conductor is a wire that connects the static wire to the ground rod.
You can recognize the grounding conductor because this wire runs the entire length
of the pole.
- A – B – C Phase
These transmission wires carry high voltage electricity from the power plants in
three phases, usually labeled A, B, and C. The three phase wires carry the power
to substations where the voltage is reduced. From the substations, the power is
distributed by lines called feeders.
Transmission wires carry electricity at voltages of 69-500 kilovolts (kV) from the
generating plants to the substations. You might think of voltage as the pressure
behind the electric current pushing the electricity to its destination.
- Supply Space
Usually the upper area of the pole, the supply space is used for electric lines
and other supply equipment. The National Electric Safety Code (NESC), started in
1913, sets the standards for the construction, maintenance, and safety of electric
lines in the United States.
The primary phase conductors are part of the distribution system wires and carry
electricity from the substations at 5-30 kilovolts (kV). On older poles, you'll
often see the primary wires supported by the crossbars.
- Step Down Transformer
The transformer, easy to recognize by its large canister shape, converts the high
primary voltage to the lower voltage needed for home use. Look closely and you'll
see that the high voltage transformer terminal is connected to one of the primary
phase conducting wires. The transformer case is attached to the ground wire on the
pole to prevent dangerous differences in voltage from developing.
- Multi-Grounded Neutral (MGN)
Distribution lines have a grounded neutral conductor to provide a return path for
the electricity. On many poles, if the distribution line is also connected to the
ground wire (or grounding conductor), the line is called a multi-grounded neutral.
Distribution lines carry electricity from the electric substation to homes and businesses.
The power in distribution lines can be one, two, or all three phases.
- Secondary Service Drop – To Load
The secondary service drop is the cable that brings electricity to the end user.
Follow the wire from your home to the utility pole, and you'll see that the secondary
service drop consists of the three conductor wires. The two insulated "hot" wires
come from the transformer, and the bare neutral wire is connected to the ground
wire at the pole. The secondary lines commonly have a voltage of 120/240 V.
- Communication Worker Safety Zone
This safety zone, also called neutral space, is the space between the lowest supply
conductor or equipment and the highest communication cables or equipment. In addition
to separating the high voltage lines and communications wires, the safety zone provides
maneuvering room for linemen and communication workers.
- Communications Space
Usually the lowest area on the pole, the communications space is used for cable
television, broadband, and telephone wires. All attachments require the pole owner's
- Communication Lines
Cable television and broadband wires are usually the uppermost communication lines.
Telephone cables are often lashed to a steel strand in the lower area of the communications
space. A true telephone pole supports only telephone wires, while a joint use utility
pole has both electric and communications cables attached.
- Utility Pole
- Poles range from 20-100 feet tall; the standard pole is 35 feet tall.
- Popular pole trees include Douglas fir, Southern pine, and Western red cedar.
- Poles are buried about 6 feet in the ground and spaced about 125 feet apart.
- The wood pole's lifespan is about 30-40 years. Sounding, drilling, and coring inspections
give information about the pole's condition.
- Attachment weight, moisture content, vibration, and settling add stress to poles.
- Utility poles may also be made of concrete, steel, or a fiberglass composite.
All plants and trees planted around poles and under wires should be trimmed regularly
to avoid interference with the electric system, especially during a storm. Utility
companies are responsible for pruning vegetation on their easements, and homeowners
can plant smaller bushes and trees that will stay below the overhead lines.
- Ground Rod
The ground rod is buried in the soil near the base of the utility pole. Since the
ground rod is connected to the grounding conductor, when lightning strikes a pole
or static wire, the high voltage surge travels down the grounding wire to the ground
rod and safely into the earth.