A wooden power pole in Lyons.

A wooden power pole in Lyons. Photo: Melissa Adams

SPENDING millions of dollars a year replacing timber power poles appears likely to continue because it would cost billions to put Canberra's electricity underground.

It would cost $15,000 to $20,000 per property to put existing power and telecommunications wires underground, according to ActewAGL.

Underground power has been put into new suburbs for the past 20 years but the astronomical expense of retrofitting existing suburbs would appear to make widespread undergrounding unlikely.

The major energy distributor says homeowners must be willing to pay some of the bill to put overhead lines underground.

The electricity distributor has looked at the options of running underground some or all of the ACT's electricity network during the past three years, and is yet to make any decisions based on the information it has.

Underground power looks better and saves money because of a variety of reasons which include lower network energy losses, less maintenance of poles and less tree trimming.

This week ActewAGL is using a helicopter to find out where trees are growing close to power lines, which could create bushfires.

Running all of the ACT's power underground would mean converting overhead power at about 100,000 properties at a cost of $1.5 billion to $2 billion.

It investigated the feasibility of underground lines in three case study suburbs - Dickson, Forrest and Aranda - chosen because they represented a variety of different conditions, and not because they were a priority for wires in the ground.

ActewAGL also looked at work by Australian National University researchers who studied people's willingness to ''buy in'' and put power underground in the suburbs of MacArthur, Calwell and Florey - all locations which have both overhead and underground power.

It found a quarter of Canberra households would pay $16,000 to put power underground, while another quarter were not willing to pay even $1000. The average was $6838.

During the past two years ActewAGL has spent millions of dollars a year replacing old timber poles in people's backyards at a cost of $10,000 each.

ActewAGL replaced 762 poles in 2011-12 - at a cost of about $7.62 million - and has so far replaced 486 poles this financial year - at about $4.86 million.

The company expects to replace poles at the rate of another 800 to 1000 poles a year for at least the next two years.

The general manager of ActewAGL's asset management, Stephen Devlin, said trials would be needed if any existing suburbs were converted to underground power in the future.

''If and when a decision is made to go ahead with a trial project, suburbs for the trial would be considered on the basis of a number of factors,'' he said.

''These factors include the willingness of homeowners to contribute financially, soil conditions and the current overhead network.''