Powerlines & Trees

Hazards From Trees

The following information has been prepared to help you to understand safety hazards that arise when trees are allowed to grow into power lines. The information summarises the main points of the Electricity (Hazards from Trees) Regulations 2003. For more detailed information on these regulations please contact Aurora, talk to your legal advisor or refer to a copy of the Regulations.

These are available for purchase from at Bennetts Government Bookshops and can also be obtained free on-line at New Zealand Legislation.

In a Nutshell

    Powerlines & Trees
  • Trees can damage and break power lines and underground cables.
  • Broken power lines and cables are dangerous and costly to repair.
  • Trees must not encroach inside the Growth Limit Zone (GLZ), which varies from 0.5 to 4.0 metres from (typical) overhead power lines.
  • Tree roots must be no closer than 0.5 metre from underground cables.
  • It is the tree owner’s responsibility to keep trees trimmed outside these distances.
  • It is Aurora’s responsibility to advise the tree owner if it becomes aware of a tree encroaching inside the GLZ, or within the Notice Zone, a distance 1.0 metre from the GLZ.
  • The cost of the first cut or trim will be met by Aurora (except for shelter belts and plantation forests).
  • Aurora can provide a skilled and site-safe tree trimming service.
  • The tree owner has the right to object to the trimming of a tree if the tree is of amenity value.
  • Failure to comply with the Regulations is an offence and if a tree damages power lines or underground cables the tree owner will be liable for the cost of repairs and damage.

What's the Problem?

Trees that are too close to power lines can cause a public hazard, widespread power interruptions including damage to consumer appliances, and damage to the lines themselves. An estimated 25% of rural power failures are caused by trees coming into contact with power lines.

  • Trees sway in the wind and this can cause them to collide with lines, causing the lines to break.
  • Trees that are in constant contact with power lines can fray the lines, catch fire, and cause electric shock to nearby people and animals.
  • Branches overhanging lines may break, breaking the line as they fall.
  • Heavy snow and rain on branches can cause overhanging branches to sag or break, causing them to make contact with the line, or even break it.
  • Some children love to climb trees and this is especially dangerous if there are power lines nearby.
  • Tree roots can grow around underground electricity cables rupturing the insulation, and causing power supply failure.

The results of tree damage to power lines can be disastrous!

  • Interruption of supply is a huge inconvenience to you, your neighbour and your community.
  • A sudden power outage can cause damage to computers and other sensitive appliances connected to the network.
  • Damage can result in expensive repair bills for which the tree owner may be liable.
  • Broken lines that have fallen to the ground often remain alive, risking electrocution and fire:
    Never approach broken lines
    Immediately call 0800-4DELTA (0800 433 582) to have an electricity service contractor disconnect the power supply to the broken lines and initiate repairs.
    Always assume that broken power lines are live until an authorised linesman has advised otherwise.
    Do not touch fences in the vicinity of broken lines, as these may have become live.
    Phone 111 immediately if there is an injury or risk of fire.

What is a 'Tree' & Who is Affected by the Regulations?

The tree regulations apply to:

  • Any tree, shrub, or plant, and any part of a tree, shrub or plant.
  • Tree owners, including home gardeners, farmers, schools, foresters and local authorities.
  • Aurora, as the owner of the electricity network in the Dunedin metropolitan area, including West Harbour, Peninsula and Taieri, and in the Central Otago and Queenstown Lakes districts. The ‘network’ is essentially the community’s electricity supply hardware (the poles, transformers and lines).

Please Note: A property owner owns the 'service' lines/cables connecting the network to their home and/or other buildings. Therefore, it is the property owner's responsibility and cost to manage any trees which may affect their privately owned lines/cables. In this instance, we suggest that you should follow these same guidelines.

Plan Before you Plant: Plan your garden, shelter belt and forest layouts before you plant. Allow for the position of trees and future growth in relation to overhead power lines and underground cables. Make sure you know exactly where all underground cables are, and do not dig holes within four metres of them.

Take Charge of Your Trees: Self-management is the best policy and you should trim your trees regularly to keep them away from overhead power lines. However, make sure this is done safely:

  • You are prohibited from working within 4 metres of power lines without permission from Aurora. To contact Aurora, click here.
  • A contractor/aborist must have written permission to carry out work within 4 metres of lines.
  • Trimmed branches must not fall within 4 metres of power lines.
  • You should be skilled in the use of a chainsaw and always wear protective equipment and clothing.
  • Provide a stable work platform and eliminate the risk of falling.
  • If the job is beyond you, call an expert arborist - phone 0800 4DELTA or see Tree Services in the Yellow Pages.

Growth Limit Zones - How Close is Too Close?

Growth Limit Zones (GLZ) are the minimum distances any tree, or part of a tree, must be kept away from an overhead power line or underground cable. We suggest that you keep trees well outside these distances to allow for tree growth and adverse weather conditions.

Overhead Power Lines:

The GLZ varies depending on the voltage and span length of the lines - see the tables below.
Not all lines in the metropolitan Dunedin and Central Otago / Southern Lakes areas are owned by Aurora.  Lines that are part of the national grid are owned by Transpower and any issue with trees near Transpower’s network should be taken up with them; visit the Transpower website.

GLZ Where Overhead Wire Span is 150m or Less
Voltage of Lines Growth Limit Zone
230-400 V 0.5m
6.6kV 1.6m
11kV 1.6m
33kV 2.5m
50-66kV 3.0m
66kV or greater 4.0m


GLZ Where Overhead Wire Span Exceeds 150m
Wire Span Horizontal GLZ(1) Vertical GLZ
150-300m 8.0m 4.0m
301-500m 15.0m 4.0m
501-700m 30.0m 4.0m
701 or greater 50.0m 4.0m

(1) Measured from centre of span. 

Underground Power Cables:

The GLZ for tree roots near underground power cables is 0.5 metres.

Notice Zone

The Notice Zone is a distance one metre from the tree to the GLZ for overhead lines. Should a tree reach this outer limit, Aurora may send you a ‘Hazard Warning Notice’ advising you that the tree is about to reach the GLZ.

When it's Time to Give Your Tree a Trim

With one exception, the cost of keeping your trees clear of power equipment is yours. The one exception is the 'first free trim' provided for by Regulation. In accordance with the Regulations, where there is no record of a previous free trim then Aurora will pay for the first trim, or for the tree to be removed, but this does not apply to shelter belts and plantation forests. If you wish to take advantage of this opportunity phone 0800 4DELTA (0800 433 582) - Delta provides Aurora with a qualified tree management service.

'Hazard Warning Notice'

Should your tree encroach inside the Notice Zone, Aurora will send you a Hazard Warning Notice advising you that the tree is about to reach the GLZ and the options you have. The notice gives you the opportunity to return to us a ‘No-interest Notice’ which means that you have no objection to the tree being removed at Aurora's cost. The notice will also advise of your rights to object to the tree being trimmed - e.g. where the tree is of amenity value and/or has historical or cultural importance.

'Cut or Trim Notice'

Should the tree encroach inside the GLZ, Aurora will send you a 'Cut or Trim Notice', which will advise you of the time limit by which the tree must be cut or trimmed. The time limit varies between 10 and 45 working days depending on the circumstances. You can arrange for Aurora to do the work, or for some other properly qualified party to do so. The notice also gives you the opportunity to return to us a 'No-interest Notice', or to express your interest in the tree and objection to having it trimmed or removed. Refer to Hazard Warning Notice above. If you have not removed the hazard or lodged an objection within the time limit, Aurora may arrange for the tree to be trimmed or removed at your cost.

Be a Responsible Tree Owner - It's the Law

It is an offence to prevent a tree that is encroaching inside a GLZ from being trimmed or removed when you do not have reasonable excuse, or have not been granted dispensation in accordance with the Regulations. The fine for this offence is up to $10,000 and if the offence is a continuing one, there is a further fine of up to $500 a day for every day that the offence continues.

The Regulations provide that, where the tree owner has been issued with and has failed to comply with a 'Cut or Trim Notice' then, in the event of the tree causing damage to power lines or underground cables, the tree owner is liable for the cost of repairs. This liability includes damage caused by the broken lines and/or by consequent power surges affecting third parties.

Let’s all work together to ensure public safety and uninterrupted power supply. Thank you.