Most U.S. states adopt the National Electrical Code (NEC) and National Electrical Safety Code (NESC) which dictate the best safety practices for public and private electrical and utility companies. These standards determine the height of power lines, from high-voltage transmission lines to drop lines located over sidewalks. However, the minimum requirements rarely match up with industry norms.
Why Are Utility Poles Different Heights?
The height of power lines is determined by the lines connected to a pole and municipal codes governing line ground clearance. Communication lines include television, broadband internet and telephone service and are located lowest in position on a utility pole. Power lines are located at the top.
As municipal building codes require greater clearance between communication lines and sidewalks or streets, the connection points for those wires move up higher. Every other line on the pole gets moved upward in the process.
In addition, there is a worker safety zone located between the communication lines and the power lines to keep utility workers safe while performing repairs and installations. As the size of this safety area changes, so does the required height for power lines.
How Tall Is a Standard Utility Pole?
It’s common to see utility poles in different sizes. Telephone wires have the lowest requirements for ground clearance. Sometimes a telephone pole doesn’t support anything but communication lines, so they wind up much shorter than neighboring joint utility poles that host high-voltage transmission lines.
It’s every electrical company’s job to ensure that their poles meet state codes. Unfortunately, sometimes they struggle to keep up with changes. The NESC released a preview of the 2020 guidelines so utilities could weigh in on proposed changes. According to the NESC, the standard height for a utility pole is 35 feet.
However, that’s somewhat controversial as communication lines have been crowding out electrical supply lines for adequate space. In practical use, 40-foot poles are the newest preferred model, though situations may call for poles of 120 feet or higher.
Ground Clearance Limits for Power Lines
The NEC calls for various ground clearance limits for power lines based on voltage and location. These minimums differ slightly from those adopted by the NESC. It’s important for property owners to contact their local municipalities for information accurate to their areas.
The NECs minimum ground clearance for power lines is:
- Sidewalks: 12 feet.
- Parking lots: 18 feet.
- Roadways, agricultural pathways: 18 feet.
There can also be different standards depending on whether the pole is carrying low- or high-voltage transmission lines.
How Tall Is a Telephone Pole?
The NESC calls for the following ground clearances for telephone lines:
- Sidewalks: 9.5 feet.
- Roadways: 15.5 feet.
- Pools: 10 feet.
This is the distance between the ground surface and the lowest point of the communication line. Companies plan on lines sagging over time due to the effects of gravity as well as temperature, bad weather and other factors. The industry minimum for attachment points on a telephone pole is 18 feet on line lengths up to 20 feet.
Longer stretches of wire experience more sag. Lines up to 200 feet in length should have minimum pole attachments of 22.25 feet. Other types of communication lines are heavier than telephone lines and so they are more susceptible to sag. These lines call for even more caution to avoid violating minimum ground clearance codes.
Telephone poles can be much shorter than electrical poles or joint utility poles. Then again, they don’t come with the same risks.
What Types of Power Lines Are There?
Several different types of power lines carry electricity from the power plant to individual businesses and homes. These include:
- Transmission lines: carry electricity long distances from power stations at 345,000 volts.
- Subtransmission lines: branch off from transmission lines to large industrial, commercial and residential areas at 69,000 volts.
- Local transmission lines: branch off from subtransmission lines to service districts and neighborhoods at 13,800 volts.
- Industrial power lines: branch off from local transmission lines to individual industrial properties at 220 to 440 volts.
- Commercial and residential power lines: branch off from local transmission lines to individual businesses and homes at 120 to 240 volts.
What Is the Voltage on Residential Power Lines?
The voltage on residential power lines is 120 to 240 volts, but homeowners shouldn’t assume this amount is safe. Low-voltage shock can be deadlier than high-voltage because of the impact on the heart. That’s why parents use child-proofing kits that block outlets.
A child who sticks a toy into an electrical socket can be killed. When it comes to danger, amps – the measure of how much current travels through the body – is more important than voltage.
What Are the Glass Things on Power Lines?
All currents are attracted to Earth’s surface. Given the chance, they’ll take the fastest, easiest route to get there. Electricity can jump several feet in order to complete this task, so safeguards were needed to contain the electricity in power lines from leaving their paths.
The glass, ceramic or plastic caps found on some utility poles prevent the flow of electricity – or information when discussing communication lines – from leaving the wire and following the pole into the ground. Companies first started producing these caps, called insulators, in the 1880s to allow electricity to travel over large distances. They’re necessary today to keep service running.
These are not the same as those brightly colored balls or other attachments hung along long, high utility wires. These markers or marker balls act as a warning to low-flying aircraft.
Are Residential Power Lines Insulated?
While most utility poles have insulators, most power lines are not insulated. Not even in residential areas. Residents often assume power lines are insulated to protect people from shock in the event of a line breaking and falling to the ground. Surprisingly, less than 10 percent of residential power lines are insulated, so why do people have this misconception?
They often mistake the weatherproof coating on the outside of electrical lines for insulation, but this is used to protect the naked wires inside, not to protect people. When insulation is installed, two things happen:
- It wears away with exposure to the elements, so it can’t really be trusted to keep people safe.
- It weighs down the line, causing more sag and requiring higher connection points on utility poles to meet ground clearance guidelines.
The drawbacks outweigh the benefits of insulating lines, so many companies opt out of the expense. That’s changing in areas where forest fires are a growing risk.
Do Power Lines Cause Wildfires?
According to the California Public Utilities Commission, about 10 percent of wildfires are started by power lines. This happens when:
- Winds blow tree branches into power lines.
- Lines snap under pressure and fall into dry areas.
- Poles break and connect live wires with grass and trees.
This is one reason utility companies, municipalities and property owners trim back trees around power lines.
Some wildfires have raged unchecked over tens of thousands of acres, killing people and causing massive destruction. Because of this, companies like Pacific Gas & Electric and Southern California Edison have paid hundreds of millions of dollars in damages and have finally started to invest more in fire prevention.
Unfortunately, placing all existing lines underground would be too expensive and destructive. Underground placement is a safer option for future developments, however, for safety and as a component of community beautification. Eventually, the standard height of power lines could be a negative number.
Do Birds or Squirrels on a Wire Mean It's Safe?
No. People who aren’t familiar with the way electricity works might make the mistake of thinking lines are insulated and therefore, safe to touch when birds or squirrels sit safely on the wires. Others think a broken line is dead if it’s not sparking on the ground. In this way, power lines are deceptive. They might look perfectly safe, but can be deadly to approach.
The reason birds and other small animals can sit on a power line without getting hurt boils down to laziness. Currents take the fastest, easiest path to where they are going. It would take needless time for electricity to leave a wire, travel through a squirrel and return to the line.
Unfortunately, sometimes when a squirrel or bird is making their way from a wire to a pole or another line, the current arcs. Instead of staying in the wire, it passes through the animal to the pole and then to the ground. The same thing can happen when people or branches get too close.
Is It Safe to Touch a Utility Pole?
People regularly attach flyers, ribbon and other articles to utility poles, but is it safe to do so? No. According to experts, stray voltage can leak down the utility pole or down nearby trees into the ground surrounding the pole. This is why electrocution is possible whether or not someone comes in contact with a live wire.
In addition, certain utility poles present other dangers. Utility poles with an X marked on the side are due to be replaced. It’s not always a matter of age, either. They could have known problems that put you at increased risk.
The same is true for the small green transistor boxes that are sometimes placed in residential areas. Homeowners should avoid landscaping around the boxes or allowing kids to climb on them during play.
Who Is Responsible for Power Lines to Your House?
When power lines break or fall and cause a fire or other incident, the utility company is held responsible. But what about other problems? In some cases, homeowners are responsible for the power lines running to their properties. How much they are responsible for depends on the type of equipment installed and the utility company.
Underground Electrical Service: In general, underground electrical service provides the least liability for homeowners, but is much more expensive to install than typical drop line or above-ground service. In the end, the property owner only has to worry about maintaining the meter base and customer conduit inside or attached to the structure.
In underground installations, the electrical company is responsible for the:
- Cable inside conduit.
- PPL conduit.
They’ll pay the tab for any repairs or adjustments needed for those parts.
Above Ground Service: Traditional electrical systems have more parts of which homeowners share more responsibility. This is one reason converting to underground service is so expensive. While the utility company covers the transistor, the meter and the service line from the utility pole to the home, the homeowner is responsible for:
- Service attachment anchor.
- Service entrance cable.
- Meter base.
- Service fuse box.
Property owners are expected to protect the equipment on their property. Any necessary repairs and any damages caused by those components are liabilities for the owner.
The standard height of power lines depends entirely upon the city and state they’re in and the types of power lines on the pole. Despite recommended minimum ground clearance levels starting at 12 feet, industry standards now lean toward 35 feet or higher.