Australian Standard AS 2209 - 1994 Timber - Poles for Overhead Lines is used to specify the requirements for wooden power poles. The standard applies to both hardwood poles with and without full-length preservatives and softwood poles with full-length preservatives.
The durability of differing wood species is categorised into Classes ranging from one to four. The most durable species are Class 1 and the least durable Class 4. Species such as box and ironbarks tend to be high durability while ash and pine are lower in durability. Note that durability classification is not the same as strength rating.
The Australian Standard will only allow the more durable Class 1 and 2 species to be used for poles that are not full length preservative treated. Any poles supplied untreated are now usually desapped and shaped. In earlier days the sapwood was left on these poles, but they tended to look unsightly as the sap started to strip off above ground. Note: The untreated sapwood of all classes of timber is very low in durability.
Two types of pressure treatments are acceptable throughout Australia:
- CCA (Water based Copper Chrome Arsenic)
The Standard specifies minimum penetration depths and retention levels for both preservatives. The standard also details information required on an identification disc and acceptable tolerances for straightness of poles, sizes, splitting and size of knots.
Normally Authorities purchasing poles make direct reference to this standard and many insist on rigorous pre-delivery inspections.
The types of timber used for poles has varied and is usually influenced by local factors. In Australia the climate ranges from tropical in the north through to drier and milder in the south. Hardwood poles have been preferred in Australia because of their natural strength with approximately 14 different eucalypts have been utilised. The most common pole types in Australia are CCA treated spotted gum and blackbutt, creosote treated messmate, untreated naturally durable species such as red/grey ironbark, bloodwood, tallowwood etc, and in Western Australia untreated jarrah. Small numbers of CCA treated pine poles have been installed on a trial basis in lightly loaded situations.
While traditionally many naturally durable poles have been sourced from old growth forests in NSW and Queensland, often local regional forests have provided poles of varying durability.
Concrete poles are now considered relatively expensive and their use is limited to special situations such as termite infested areas etc. |
