Vegetation Management FAQ

See some of our most common questions regarding our vegetation management work.

Trees are the leading cause of power outages in our region. We prune 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:

  1. Safety - Trees touching power lines can put stress on live wires and cause branches to burn and fall to the ground, sometimes causing fires in trees or nearby buildings. Trees near power lines are dangerous because they create a potential path for electricity to travel to the ground. People coming into contact with this path (by touching, climbing, trimming, or cutting down the trees) are at risk of being electrocuted or receiving significant electrical burns.
  2. Storm-related outages - Wind, snow, and ice often damage trees causing branches or entire trees to fall on power lines, resulting in power outages that can last for days.
  3. Voltage loss - Trees touching power lines drain electricity from the electrical system resulting in voltage loss that can damage motor-driven appliances in homes, such as refrigerators or washing machines, and sensitive electronics such as computers.

We trim trees on a 4.5 year pruning cycle to maintain safety while keeping costs low for our customers.

There are several situations that may require your tree to be trimmed:

  • Strong winds cause the tree to make contact with the wires.
  • The wires sag due to high temperatures that cause the wires to contact the tree.
  • Wet, rainy weather is causing branches to droop.
  • Your trees may not be touching the wires now, but they may before the next pruning cycle. We plan ahead for potential problems.

We prune trees located within our complex distribution and transmission system.

Distribution path of electricity

  1. Power is generated from dam/powerhouse
  2. Substation transformer steps up voltage for transmission
  3. Transmission lines carry electricity long distances
  4. Neighborhood substation transformer steps down voltage
  5. Distribution lines carry electricity to residents
  6. Transformers on poles step down electricity before entering residence
  7. Service line for resident 

Public and privately owned trees that are within the power line clearance area and could impact power assets are pruned. Vegetation is pruned away from private service lines for the first 10 feet from where these connect to the Distribution Power Lines.

City Light FacilityDescriptionClearance Objectives
Distribution Power Lines Primary Voltage 10 ft. for slow-growing species
14 ft. for fast-growing species
15 ft. overhang clearance
Service Lines and System Neutral Lines 3 ft. for slow-growing species
5 ft. for fast-growing species
City Light prunes vegetation away from Service Lines for the first 10 ft. from where they connect to utility poles
Transmission Power Lines 115,000 Volt Based on line-engineering, species, trim-cycle, and right-of-way width
240,000 Volt Based on line-engineering, species, trim-cycle, and right-of-way width
Infrastructure Underground Vaults Vaults must be accessible for maintenance work
Power Meters Meters must be accessible
Transformer 10 ft. clearance for all tree species
Utility Poles 3 ft.

What trees do you prune?

We prune trees located between poles and within the first 10 feet from where they attach to utility poles. Maintaining clearance after the first 10 feet is the property owner's responsibility. While this is not a high-voltage line, we do recommend that you hire a professional service to do the pruning. Make sure to check with us before beginning to ensure safety precautions are met. A list of tree company permits registered to work on Seattle Department of Transportation right-of-way property may be found at: www.seattle.gov/transportation/treecompanypermits.htm  

We also provide a 24-hour power disconnect so that this work can be done safely. Please contact us to request disconnect service at:

North of Denny Way: (206) 615-0600 

South of Denny Way: (206) 386-4200  

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 they must have the necessary permits. City Light must assess trees for electrical hazards and may provide a free "make ready" pruning, if appropriate. In most cases, City Light will prune the trees to reduce the risk of trees making contact with electrical assets. This is called a "make ready." To have your trees assessed for potential electrical hazard, call (206) 386-1650 or contact us online

Yes, if you notice an urgent hazard such as a broken tree limb on a power line or trees in the lines causing them to droop or spark, please call (206) 684-3000 to be connected to a customer service representative. City Light does not prune trees from privately owned communication and cable lines. To report non-emergency issues with trees in power lines, please report a tree problem or call (206) 386-1733, Monday-Friday between 8:00am and 4:00pm.

Yes. Our crews remove tree limbs and any debris created when trimming trees. Usually, the logs are cut into firewood and left by the right-of-way.

During a severe storm, we may not always be able to remove debris as crews may need to make repairs and move on quickly to proceed with power restoration work.

As an electrical utility, we are responsible for maintaining our system and to protect the health, safety and general welfare of the public. At times, we will require access to a customer's property to inspect, maintain, and repair the electrical system. We always try to notify you before coming onto your property unless there is an immediate and present emergency involving a tree on your property.

Before planned pruning work begins, a City Light representative will knock on the door of homes and buildings near the tree pruning area to give notice about the upcoming pruning work. They will leave a door hanger with tree pruning information and a contact phone number if you're not home.

If a tree has caused an outage or poses a safety hazard, the work may be done immediately, and you would be notified after it is complete.

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.

If a tree poses a safety hazard, or if pruning will risk the health and overall stability of the tree, we will work with you to remove it. Unless there is an emergency, we will contact you in person or in writing before removing a tree from your property.

Customers sometimes ask us to remove a tree rather than prune it. We evaluate these requests to understand the problem first. In some situations, we will remove the tree.

Learn more about Urban Tree Replacement.

There are many obstacles to installing power lines underground.

  1. Existing trees and their root systems would be impacted, undermining the health and stability of the trees.
  2. Considerable expense, time, and disruption would be involved in trenching through existing road systems and landscapes.
  3. The cost of designing, engineering, and installing an underground system in an established neighborhood is very high.
  4. Customers would have to pay for an underground system.
  5. 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.
  6. If there is a fire in an underground vault, our crews cannot make repairs until it is safe to enter the area.