A large tree I planted several years ago is getting close to the overhead powerlines in front of my house. Who is responsible?
Trees that are too close to powerlines can be hazardous. It is the tree owner’s responsibility to keep trees trimmed to a safe distance away from powerlines. If the lines company becomes aware of a tree growing too close to powerlines they can issue a cut or trim notice.
The line owner must meet the cost of the first trimming (i.e. the first time a notice is issued) or they will trim the tree directly. If this is the case they are also responsible for removing or tidying any debris from this cutting. Any subsequent trimming, to prevent your tree from growing too close to the powerlines, will be your responsibility and at your cost.
If you fail to comply with a cut or trim notice you can be liable for a substantial fine.
The Electricity and Gas Complaints Commission has a handy 
overview of the process
I want to plant a tree in my front yard but am not sure if there are underground power cables there. What is the best way to check?
Never start digging without locating underground cables and services such as water and sewer lines. If you’re not sure where power cables run you can check with the power companies in your area. They should be able to locate and mark the position of the cables. Be careful as cables are not laid in a straight line and can vary in depth.
If you suspect damage to a cable then contact the owner power company right away.
You should also check whether there are any other underground services in the area you want to dig. Your local council can tell you about any local utilities such as water, stormwater and sewerage drains.
Energy Safety recommends that you hire a location service contractor, as they specialise in locating underground cables and other services.
You can use a service called B4Udig (http://www.beforeudig.co.nz 0800 248 344) where you register your planned work and they will pass this onto each organisation which has cables which may be damaged by your work, so that they can contact you directly with any concerns or safety instructions.