Nearly one-third of power outages can be traced to tree interference. Seattle City Light prunes trees to promote reliable electrical service and to maintain a safe environment. Trees that grow into the power lines can cause problems in three ways:
Safety: Trees directly touching power lines put constant stress on live wires and cause branches to burn and fall to the ground, sometimes causing fires in trees. The electricity in power lines poses no danger to you until it comes into contact with a ground or something touching the earth - like a tree. A grounded contact provides an alternate path for electricity to flow through, creating a safety hazard and a potential outage. The potential for electrical shock exists if a person causes a limb to touch a live wire or if something they are carrying, like a pole pruner, makes contact.
Voltage loss: Trees touching power lines drain electricity off the electrical system resulting in voltage loss. Low voltage can damage motor-driven appliances such as refrigerators or washing machines, and sensitive electronics such as computers.
Storm-related outages: Wind, snow and ice often damage trees. Branches, limbs and entire trees can fall on power lines, tearing down energized lines, transformers and poles. The resulting power outage can rob you of heat, lights, communication and refrigeration. During very severe storms, outages can last for days.
Seattle City Light’s goal is to deliver safe and reliable electric service to you and your neighbors. In order to accomplish this, we need to maintain a safe distance between your trees and our wires.
Our standards are based on several factors: the minimum safe working distance for a tree worker, how much trees sway in high winds, the ability of limbs to break and fall on lines and the varying growth and re-growth rates of different species of trees. The minimum distance for most distribution voltage within the SCL system is 10’ tree-to conductor clearance.
To maintain this ten-foot clearance, we must consider how much the tree will grow between pruning cycles. We are working to achieve a four-year pruning cycle.
Seattle City Light contractors prune using a method called directional pruning. Directional pruning, removes only those branches that conflict with power lines. Rather than cutting limbs back to unsightly and unnatural stubs, branches are pruned back to the center of the trunk where trees normally shed them. We do not shape or round-over trees because it’s not good for the health of your trees. Future tree growth is directed away from the power lines.
Our goal is to keep your tree alive, healthy and out of harm's way. City Light has certified arborists in the field and in-house. They are directly involved with pruning the trees to ensure that proper pruning techniques are used to preserve the health of the trees.
Our contracted crews are required to work according to approved standards to ensure the health and well-being of the trees. They are trained and certified annually to prune trees from power lines.
The pruning methods we use are endorsed by the International Society of Arboriculture. Although the initial prune with the directional pruning technique may appear severe, this method is recommended over topping or rounding-over trees. Directional-pruned trees are less susceptible to disease and insect problems, and the overall structure of the tree is stronger, more resistant to high winds and heavy ice. Directional pruning removes only those branches that pose a threat to power lines. Future growth is directed away from the power lines.
Before pruning work begins, a City Light representative will knock on the door of homes and buildings adjacent to the tree pruning area to give notice about the upcoming pruning work. If no one is there, they will leave a door hanger with tree pruning information and a contact phone number.
However, under emergency conditions, if a tree has caused an outage or poses an imminent safety hazard, the work may be done immediately and the customer notified following the job.
For large projects, City Light will place a tree pruning notice in the local neighborhood newspaper and notify the district neighborhood council. A Utility representative will provide information at meetings upon request.
Our service territory covers 131.31 square miles. We are working towards a 4-year pruning cycle. Any increases to that schedule would require more crews than have been authorized by the City Council.
We consider several factors when determining whether to prune a tree. Will strong winds cause the tree to make contact with the wires? Will movement in the wires, such as sagging due to high temperatures, cause the wires to contact the tree? Although your trees may not be touching the wires now, we plan ahead for potential problems.
State and federal safety regulations require that anyone working within 10 feet of a high-voltage electrical line must have proper training and certification. Most private tree companies do not meet this requirement. Before these companies can prune or remove trees, City Light must first prune the trees to minimize or eliminate the risk of branches falling into the lines. This is for your safety.
The power lines that run from pole to pole carry high-voltage electricity. Each year, a number of amateur tree pruners are seriously injured or killed when they come into contact with an energized line directly or indirectly through tools or tree limbs. Poles, ladders and elevated lifts can easily provide a dangerous electrical path if they make contact with an energized line. By pruning your own trees, you may be putting yourself in a dangerous position. We recommend that you hire a professional service and that you check with City Light before beginning.
City Light prunes trees located between poles. Maintaining clearance around the service drop (the wires that run from the pole to the home) is the property owner's responsibility. This is not a high-voltage line; however we recommend that you hire a professional service to do the pruning. Seattle City Light will provide a 24-hour disconnect so that this work can be done safely. Following are contact numbers for requesting this service.
If the tree poses a hazard to safety and property, or if pruning will undermine the health and overall stability of the tree, we work with the property owner to remove it. Unless there is an emergency, we will contact you in person or in writing before removing a tree from your property. With city-owned trees, we contact your local government. Customers sometimes ask us to remove a tree rather than prune it. We evaluate these requests on a case-by-case basis. In some situations, we will remove the tree.
As an electrical utility, we are responsibile to maintain our system and to protect the health, safety and general welfare of the public. Customers must allow access to their property at reasonable hours to inspect, maintain and repair the electrical system. We would notify you at least one week in advance, before coming onto your property unless there was an immediate and present emergency involving a tree on your property or entangled in overhead wires that cross your property.
Normally our power-line clearance contractor removes tree limbs and the debris we create. The logs are cut into fireplace lengths and left by the right-of-way. Generally, cut logs are left for the public, if the customer does not want it.
When tree debris is caused by a severe storm, we do not always remove it. Our crews must work quickly to remove hazardous downed wires and make repairs to restore power to thousands of customers. In these situations, our crews cut broken and uprooted trees so they can access the damaged area to make repairs. Brush and wood may be left at the site so that they can proceed with other restoration work. Typically, the City and County make allowances for after-storm debris disposal that their solid waste facilities.
You can request wood chips from our contractor, Asplundh Tree Experts Company at (425) 483-9339. If the chips are available and Asplundh is in your neighborhood, they will deliver wood chips to you. You must be willing to accept a full dumptruck load.
There are a number of obstacles to placing all the power lines underground. Existing trees and their root systems would be impacted, undermining the health and stability of the trees. Considerable expense, time and disruption would be involved in trenching through existing road systems and landscapes. The cost of designing, engineering and installing an underground system in an established neighborhood is very high. Customers would have to pay for an underground system.
In general, maintenance, repair and rebuilding underground systems are more complex and expensive because the lines and structures are buried and hidden from view and not easily accessible. Also, if there is a fire in an underground vault, our crews cannot make repairs until it is safe to enter the area.
Please do not plant vines, shrubs or trees directly adjacent to or on power poles. Keep all vegetation at least 10 feet away from the poles. Our crews must have quick access to climb poles when making repairs.
Depending on the species, young trees mature to different heights. When you select new trees, anticipate the height and spread of the mature tree in relation to power lines.
Trees planted directly under or within 20 feet of the power lines should have a mature height less than 25 feet.
Trees that mature to 25 to 45 feet should be planted 20 to 50 feet away.
Trees greater than 45 feet at maturity should be planted more than 50 feet away.
Smaller trees will remain healthier and look more natural without pruning. They will enhance your neighborhood environment while maintaining a safe, reliable electrical service. We offer the Urban Tree Replacement Program to Seattle's neighborhoods. If you would like more information on this program, call
(206) 386-1902.
City Light promotes the right tree in the right place. We offer a free publication,
The Right Tree Book,with information on selecting and planting appropriate trees and shrubs around utility lines. To request a copy, call City Light at
(206) 684-3000. Or you may print out a copy from the Urban Tree Replacement Web site.
Yes, if you notice an urgent hazard such as a broken tree limb on a pole-to-pole power line or trees in the lines with arcing and sparking, please call our Electrical Emergency Line,
(206)706-0051, immediately. To report other problems with trees in powerlines (located between poles), call
(206)386-1733. City Light will schedule an inspection to determine what the problem is and how it should be resolved.
Only Qualified Line Clearance Tree Trimmers may work in proximity of our distribution or transmission power lines. If you want to have a tree removed which is too close to these lines we will perform a "make ready" at no charge to you, assuming all necessary removal permits are in place. This means we will remove as much of the tree as necessary to eliminate the potential electrical hazard to a non Qualified Line Clearance Tree Trimmer, making the tree "ready" for removal. As with all other work, City Light will remove all brush leaving burnable firewood on site.
If you want a tree pruned which is too close to these lines, City Light may be able to remove a portion of the tree to allow for non Qualified Line Clearance Tree Trimmers to enter it. City Light is not able to prune trees other than to attain required clearances and/or to perform a Make Ready. All of City Light's contracted companies have Qualified Line Clearance Tree Trimmers on staff and may be available to work in a trees without a Make Ready.
Call (206) 386-1733 or e-mail respond.scl@seattle.gov
. A City Light employee will respond to your questions or concerns, usually within two working days.
Urban Tree Replacement Program
There are times when the most appropriate action is tree removal. Dead, diseased or inappropriate trees should be replaced with trees more compatible with overhead power lines. Smaller trees are healthier and more natural looking and will enhance your neighborhood environment and allow us to provide a safe, reliable service to all our customers. Seattle City Light promotes the right tree in the right place and has a neighborhood tree planting program called the Urban Tree Replacement Program. Seattle City Light also sponsors neighborhood plantings. If you would like more information on this program, call (206) 386-1902.
For your free copy of "The Right Tree Book", call City Light at (206) 684-3000. Or you may view the Urban Tree Replacement Page
to download and print your own copy in Adobe Acrobat (*.pdf) format.
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