When a tree is allowed to grow close to the power lines it can have serious consequences, both with causing disruption to the flow of power in the region, and also to the safety of any person or animal who could come in contact with the problem tree.
Trees growing into power lines can become an issue when the branches come in to contact with more than one conductor, or if a branch above the lines breaks off and lands on them. Even trees that are planted quite far away could still uproot and fall across the lines, or with certain species of Gum (Eucalyptus), can shed bark that is carried toward the lines in strong winds.
It is the responsibility of the tree owner - not the network owner, to ensure their trees are kept clear of the power lines. The best way to do this is to arrange pruning of the tree when it is 3 or 4 meters away from the nearest conductor, this way it can be done safely and reasonably quickly, thus saving you money on trimming costs.
Some network owners (such as Waipa Networks) will even offer to cover the cost for removal of the tree at ground level, as this reduces the overall potential for faults on the network. Each network owner is different though, so it pays to do your homework to ensure you don't receive any unexpected bills for tree trimming.
For further information on the government legislation around trees and power lines visit: http://www.legislation.govt.nz/regulation/public/2003/0375/latest/DLM233405.html or contact the friendly team at Waikato Tree Services for a free quote and assessment on your trees.