Ausgrid has an ongoing maintenance program to keep trees and their branches clear of powerlines and power poles. This helps prevent injury to people and damage to property. About 60% of all outages on our electricity network are caused by external factors like trees coming into contact with powerlines, so tree management can also have a significant impact on the reliability of your electricity supply.
The law requires street trees to be trimmed to ensure there is a minimum safety clearance between trees and powerlines. Ausgrid is doing this work to protect you and your environment. Where a tree on private property is entering the safety clearances of wires in the street, Ausgrid will trim the tree for residents, free of charge, to meet our safety obligations.
How will the trees look?
In residential areas the vegetation safety clearance is typically 1.5 metres around bare, low voltage overhead wires and two metres around power poles. However, the safety clearance depends on the voltage of the overhead wire - the higher the voltage the larger the clearance.
Trimming also allows for regrowth (based on tree species and environmental conditions), in addition to the minimum safety clearances so vegetation should not grow back within these clearances before the trees are trimmed again.
For most species of tree, once the minimum safety clearance plus an allowance for regrowth is determined for each branch, it is trimmed at the nearest growth point or collar outside the limit of clearance required. This is a requirement under Australian Standard AS4373 as trimming at a growth point protects trees from infection or disease and minimises the development of weakly attached growth (see illustration).
Unfortunately it is not always possible to achieve an aesthetically pleasing result, because of the:
- species of the tree planted, and
- position of the tree, ie: it has either been planted too close to the mains, or even planted directly underneath.
Are there any other options?
Councils are offered the option of installing Aerial Bundled Cable (ABC) which wraps the four Iow voltage overhead wires, strung between poles along suburban streets, into one single insulated cable.
The safety clearances required for ABC are less than for uninsulated wire. Trees that have already been trimmed for uninsulated wire clearances will take some time to regrow to the ABC safety clearances. ABC also reduces the likelihood of a power interruption, which can occur when uninsulated lines touch and then short-circuit. In some instances, this can cause live wires to fall to the ground.
Underground electricity is also installed in new urban residential developments. Many new high voltage wires are also placed underground, and in some commercial areas, overhead wires are placed underground in conjunction with building developments.
Comparative costs for low voltage overhead in an urban area
Keeping the existing overhead and trimming trees that are located within clearances of the powerlines is the most economic option for the community (and free to residents) provided environmental issues are suitably managed.
Replacing bare overhead wires with Aerial Bundled Cables (ABC) is a moderately expensive option. Trimming trees to reduced clearances will still be required.
Replacing overhead wires with underground cables is the most expensive option. Ausgrid considers all requests for undergrounding on a case by case basis in accordance with the "Network Undergrounding Policy Guidelines."
Relocating powerlines to avoid vegetation, or removal of the vegetation, varies in cost and will depend on a range of technical, social and environmental issues. These jobs are generally done on a ‘beneficiary pays’ basis.
What does trimming achieve?
Tree trimming reduces the risk of:
- accidental electrocution,
- fires caused by electricity, and
- power interruptions caused by branches touching overhead wires.
Do workers know how to trim trees?
Trimming is carried out by contractors who follow the Australian Standard AS4373 Pruning of Amenity Trees.
Ausgrid employs a horticulturist and an arborist to audit the work of our contractors. Each contractor also employs a horticulturist and an arborist to monitor standards and ensure they are maintained.
Trimming or removal of trees near powerlines can be extremely dangerous. If trees are within three metres of our powerlines, only vegetation management workers authorised by Ausgrid are permitted to carry out the work.
What trees are best to plant near powerlines?
Check out our general information on planting near powerlines and contact Ausgrid, your local council or nursery for advice. Where possible, avoid planting near a powerline. You must also obtain permission from your local council if you are planting on the nature strip.
If you have any questions, check out the links for more information. Can’t find what you need, please call us on 13 15 35