In order to assure safe, reliable, electric service the utility companies must prune branches away from high voltage electric lines. If branches make contact with these lines they can cause power outages. Worse yet, if a tree that has branches growing up into energized lines is climbed by children or adults, electrocution may occur. Every year people are severely burned and killed when they climb trees and make contact with electric lines.
In the past, utilities obtained line clearance by “topping” trees or “rounding” them over every few years. These techniques give little consideration to tree health or structural integrity. Current research shows that topping or heading cuts create entry points for wood decay. This slowly weakens the tree internally, shortening its life and in many cases causing future storm damage.
Directional or through pruning is the most appropriate way to prune trees for electric utility line clearance. Trees are no longer “topped” or “rounded-over”. Directional pruning involves the removal of branches that are growing towards the conductors in favor of those growing away from the conductors. These branches are pruned properly back to a lateral branch that is 1/2 to 1/3 the diameter of the branch being removed. This allows for good wound closure and reduced water sprouting.
Directional or through pruning removes less leaves needed for food making, pruning fewer branches thereby reducing internal decay. Trees growing directly under conductors will appear ‘U’ or ‘V’ shaped. Trees growing alongside a conductor may appear ‘L’ shaped from side pruning. At first the tree may appear misshapen, especially when looking down the curb-line, but it changes over the years as the tree grows. Looking at the tree perpendicular to the lines (straight at the house from across the street) the tree appears natural with lines running through it. Directionally pruned trees stay healthier than topped trees and result in less pruning in the future.
Questions about Trees and Utilities, a PA Community Forestry Fact Sheet
Pruning for Utility Clearance, a PA Community Forestry Fact Sheet
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