Mitton Consulting has completed the proposed testing programme for earthing solutions for work on wooden poles which was approved by the SSPG. Testing of concrete poles has been limited due to poor results (the earthing arrangements to be tested were described in Newsletter No 2). Mitton Consulting has also completed earthing arrangement tests on wooden poles for Transpower. Testing for the EEA commenced later than scheduled due to weather delays and the need to arrange specific procedures required for the testing.

As a result of the preliminary findings obtained during the Transpower tests on the potential effectiveness of downleads attached to wooden poles, the testing scope for the EEA was expanded to include tests on this configuration. Test results obtained for wooden poles have been consistent and repeatable, and provided a suitable level of confidence in the relative effectiveness of the tested solutions. Some solutions are not sufficiently effective, no solution is totally effective by itself, but some solutions provide potentially good outcomes particularly in conjunction with good work management practices. Results of the tests originally scheduled for concrete poles were disappointing, and did not identify a possible solution.

The results of the testing to date were discussed at a meeting of the Earthing Working Group (EWG) prior to Christmas, and actions for the immediate future identified.

Due to the poor results from the initially agreed concrete pole test programme, a small number of tests have been carried out which used an electrical contact with the reinforcing of the pole. These tests have demonstrated that significantly reduced shock currents can be achieved by this means.

Due to the risks associated with accessing reinforcing in poles, particularly for pre-stressed poles, expert advice is being obtained on this practice before further testing takes place. It is possible that this solution will not be deemed practicable for field use. However, the EWG will be recommending that all new concrete poles are manufactured with an integral earthing system.

Test results have been evaluated by Mitton Consulting and a draft report prepared. The report includes recommendations on earthing solutions for wooden poles which could be used for field work. The report was reviewed by the EWG at a meeting in late January. The EWG has identified the solutions which will be further refined.

The earthing solutions which are determined to be practicable for field purposes will be documented in the EEA Guide for Temporary Earthing. The solutions which will be adopted will need to be used in conjunction with management practices, as they are practicable steps for improving safety rather than complete safety solutions. The Guide will also document supporting management practices such as hazard identification, effective isolation, and hazard controls. A revised draft of the Earthing Guide is to be available for the workshops which are proposed to be held in late March, although the issue of concrete pole earth bonding will possibly remain outstanding.

The expected dates for completion of testing, and revision of the Earthing Guide, have been amended as follows:

•     Field tests for concrete poles to be carried out when advice on accessing reinforcing is received.
•     Analysis of results for wooden poles, and approval by EWG, by late January.
•     Preparation of revised draft Earthing Guide by end of February.
•     Approval of revised draft Earthing Guide at the SSPG meeting of 28 February.
•     Industry workshops in late March.
•     Finalisation of Earthing Guide by end of April (depending on concrete pole testing).

The SSPG reminds the industry that the Notice to Industry (Work on Overhead Conductors) published in September 2005 is still its latest and most relevant guide on temporary earthing. 

The SSPG also reinforces the priority which must be given to hazard identification. Temporary earthing and equipotential bonding is a necessary hazard control, but work parties must focus 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.

Readers should also refer to the incident announcement on the EEA website involving the relivening of conductors while a work party was still working on them, and the issues identified in relation to the temporary earthing. For a copy of the report (Safety Advice 10-2006 (NZ) Re-Livening Prior to Completion of Work), please click here.