Workshops were held on 21 March in Christchurch and 23 March in Auckland with over 100 attendees. The purpose of the workshop was to disseminate the EEA recommendations for portable protective earthing practices, and included was a description of the research and testing carried out, and an overview of the changes to the Technical Guide.
For copies of the workshop presentations, please contact the EEA Office.
The field testing carried out indicated that:
A draft of the revised Guide to Work on De-Energised Distribution Overhead Lines was provided to workshop attendees. The Guide contains all guidance being provided by the EEA for work on poles, and will replace the current version of the Guide (previously titled 'Guide to Temporary Earthing of Distribution Overhead Lines') (Jan 2005) and the Notice to Industry (September 2005).
The draft was available for consultation, with comment due at the EEA by 27 April 2007. The EEA intends to publish the Guide by the end of May.
Amendments have resulted from research and testing carried out on wooden and concrete poles to determine the most practicable means of providing temporary earthing and the creation of equipotential zones. As a result of the work, practicable means are provided for creating acceptable earthed equipotential zones at work sites for wooden poles and concrete poles with integral earthing.
For existing concrete poles without integral earthing, a practicable method for bonding to the concrete in these cases was not found and hence different approaches need to be taken to manage the potential hazardous voltages which may appear during inadvertent single phase livening.
In addition, the structure of the Guide has been re-organized. It now commences with planning and hazard management, and requires the establishment of equipotential zones in conjunction with temporary earthing. The consultation draft of the Guide contains few diagrams, but it is intended that the issued version will contain more.
Those providing comment on the draft were also asked to provide:
The testing carried out on concrete poles clearly demonstrated the effectiveness of bonding the pole reinforcing into the equipotential zone, and without the ability to bond the reinforcing the pole must be considered partially conductive and managed as described above. As a consequence, the EEA is recommending that all new concrete poles are manufactured with integral earthing, or an equipment earthing system. The requirement applies to pre-stressed poles as well as bulk reinforced poles. Details of the design method are to be arranged between the purchaser and the pole manufacturer.
Factors to be considered in the manufacture of new concrete poles include:
Consensus at the Auckland workshop was that the integral earthing connection point would be termed a 'bonding point'.
Due to the risks associated with accessing reinforcing in poles, particularly for pre-stressed poles, expert advice has been requested on this practice. To date the indications are that a solution will not be feasible and therefore this solution will not be deemed practicable for field use. Any updates on this issue will be disseminated when they are available.
The actions which asset owners and employers need to take are:
Work to be completed includes:
When section 6 of SM-EI Part 3 is reviewed it is likely to be arranged to reflect the emphasis of the Earthing Guide.
The SSPG reinforces the priority which must be given to hazard identification, both at the work planning stage and when at the worksite. Temporary earthing and equipotential bonding is a necessary hazard control, but the focus must be on means to prevent inadvertent livening from occurring from any source including over or under passing live conductors and adjacent live conductors on the same structures.