Tree Trimming

NBU Tree Trimming Standard


Trees are valuable assets in commercial, private, and public landscapes. Trees add aesthetic beauty, modify and enhance the environment, serve architectural and engineering functions, and increase property and community economic values. These same trees that enhance landscapes, however, can be a major challenge for NBU in terms of system reliability and expense.


Most people have grown accustomed to reliable, uninterrupted electric, telephone, cable, water and sewer service in their homes and offices. Unfortunately, trees are one of the major causes of power outages in areas of overhead utility lines due to limbs having direct contact with lines, or when trees or tree limbs fall on the lines. Tree root systems can also penetrate underground water and sewer lines and disrupt service.


When trees contact live wires, they become conductors of electricity. This can cause power outages or create dangerous situations for anyone coming in contact with the trees. The annual cost of labor and materials for tree pruning and removal is significant and ultimately is a cost shared by all NBU customers. This maintenance work is necessary to protect the public and our employees who service the lines, as well as to ensure safe, reliable electrical service.


NBU strives to maintain continuous electrical service and public safety by striking a balance between nature's beauty and operational requirements.


Tree and Vegetation Management

Often it is the practice of planting tree species with potentially inappropriate mature heights that increases the likelihood of problems later. Customers are advised to check their easement documents which provide diagrams of utility easements that are in place for their property as well as s the specific language that grants NBU the right to remove and or trim trees which may endanger or interfere with the efficiency or maintenance of utilities.


NBU typically employs a contracted company to prune trees and control vegetation in its easements and right-of-ways. The contracted workers have been trained and certified to work close to high voltage power lines. Tree pruning is performed by workers who either climb trees using special equipment or, where possible, use an aerial lift or ‘bucket truck’ to mechanically elevate themselves into position to access and prune the limbs close to the electrical wires. Sufficient branching will be removed from “target” trees to assure limbs will not contact the wires before the next scheduled maintenance event.


Line clearance methods for existing utility line/street tree conflicts include natural, lateral, and directional pruning. While people sometimes find this necessary pruning to be aesthetically unacceptable, these pruning methods have been developed by industry professionals to minimize the impact of pruning on tree health while encouraging the tree and new growth to grow away from the power lines and equipment. In addition, contractors use a chemical treatment on cut branches of oak trees and on tree stumps to seal and prevent oak wilt infestation from the cut area. NBU also requires contractors’ trimming equipment to be sterilized in order to prevent the spreading of harmful tree diseases.


Unfortunately, people often find this necessary pruning to be aesthetically unacceptable. Because of the inherent danger of electric lines, any pruning needed within easement areas should only be carried out by professionals trained in line clearance pruning, never by homeowners. NBU tree trimming professionals follow Best Management Practices for Utility Pruning of Trees. These practices were developed from the residential and commercial tree care industry, utilities, the municipal and federal sectors, the landscape and nursery industries and other interested organizations and are documented in American National Standards Institute publication ANSI A300, part 1.




Scheduled Maintenance Events

NBU strives to maintain a trim cycle every 4 to 5 years.  This means our employees and contractors will access your property in order to inspect the right-of-way and perform any necessary tree pruning to keep the line safe and operable until the next scheduled visit. Several days prior to work in your neighborhood, the line clearance contractor will leave a work notification card (door hanger) at the front door (or gate) to advise you of their intent to return to perform any work necessary. If you have questions or concerns regarding the work, please respond by calling the number indicated on the notification card.


Trimming Specifications:

The trim distance NBU uses depends on the nature of the electrical equipment. Primary power equipment is equipment that conducts current at several thousand volts. It is the equipment associated with electrical distribution on the power grid. Overhead primary wire is not insulated. Secondary power equipment is the electrical equipment and wire that supplies current to your residence. It conducts current at a few hundred volts and usually has insulation on the wiring.


For Primary equipment, contractors will trim a minimum of 8 feet back from all wires and also remove all overhanging limbs and branches above the wires and equipment. They will also remove all new or small trees that are growing directly under the line to prevent future tree contacts and trimming issues. 


For Secondary equipment, contractors will trim a minimum of 3 feet and then recommend directional growth trimming away from the service drop and, if possible, the removal of any large limbs over the service drop that could fall and disrupt service to your premises.

 The contractor will also trim a minimum of 3 feet around utility poles. For any underground equipment, trees are trimmed and shrubbery cleared within 10 feet of any equipment door or entrance way and 3 feet on the side and back. Underground equipment is air-cooled, thus space on the sides and back is needed to ensure an unrestricted flow of air. When NBU employees work on underground equipment, they often use 8-foot sticks for fuse change-outs that requires a 10-foot clearance in front of the door and a 3-foot clearance on the sides and back to ensure they can safely and effectively manipulate the  items.


How You Can Help:

Before planting new trees or shrubs, look overhead and all around the intended site. Note how far the planting site is from overhead utility lines, underground equipment, and the utility easement. Always consider the mature size of the tree or shrub and place these accordingly. In this manner, you can avoid the need for significant trimming or even removal due to easement encroachment or equipment restrictions.


For plant selection, determine whether the proposed planting site falls into a low, medium or tall tree height zone (see illustration below). The low height zone extends 15 feet on either side of overhead wires. Plant large shrubs and small trees with mature heights of 20 feet or less within this area. To account for the width of taller trees, the medium height zone begins at least 15 feet from all utility lines and may include the area that frames a building or residence. Select trees that grow 40 feet or less for this zone. The tall height zone begins at least 35 feet from buildings and 65 feet from utility lines. Tall trees need additional space to permit adequate root development and to minimize structural storm damage. Select trees that grow taller than 40 feet for this area. Use tall trees in wooded lots, parks or other open areas where their height and spread can be appreciated without becoming a liability.



When selecting a particular tree species, consult a reference that will provide the tree's mature height and spread. When selecting urban trees, avoid those that require high maintenance (frequent pruning, control of major pest problems, etc.) or drop messy fruits, leaf litter and twigs.


Look for trees that can tolerate generally adverse urban conditions (limited soil volume and moisture, compacted soil), and that have a slow to moderate (never fast) growth rate. Always follow proper tree and shrub planting guidelines and call 1-800-DIG-TESS before you dig any planting hole.


NBU Electric Operations employees are also available to help advise customers about tree and vegetation placement and management. To request a tree trimming consultation during regular business hours please contact Control Center at


***References include NBU Website and BTU Website