The fatal accident at Arahura in January 2005 focused the industry's attention on temporary earthing.  Since then research and testing has been carried out on temporary earthing practices, a 'Notice to Industry' has been published, and two workshops held.

Research and testing carried out so far was completed prior to the two earthing workshops, held in early March 2006.

Research into published papers on earthing has found that the cluster mount is adequate when used in conjunction with good earthing.  For example, testing in the United States has found that the cluster mount is effective when used with an earthing system such as HV neutral wires.

Testing of temporary earthing arrangements was carried out by Mitton Consulting on a selection of poles.  All tests were yard based and carried out with the pole horizontal, and simulated the installed arrangement.  The results of the tests were presented at the earthing workshops held in early March.  Based on the limited testing carried out the key results were:

• The cluster mount typically provides a high resistance connection to the pole due to the high resistance of the outer layers of wood.  The inner section of the pole retains more moisture and is therefore more conductive.  While the cluster mount was found to provide an improvement for temporary earthing purposes, it does not normally provide an adequate electrical connection by itself.
• Significant reductions in shock current were obtained with the use of spikes embedded at least half way into a pole, with greater improvements being obtained from additional spikes.  Spikes were tested in conjunction with pole cluster mounts.

The earthing workshops held in Auckland and Christchurch in early March were well attended, and many important ideas, issues and suggestions were presented.  The future testing programme will use ideas from the workshops, and generous offers of assistance for field testing.  The workshops covered an overview of earthing principles and reinforced expected field practices, as well as providing information on the results of testing.

The SSPG has considered the results of testing to date, and considered suggestions on what testing should take place in the future.  The SSPG has agreed to the ongoing focus of testing and will shortly be reviewing a detailed test programme.  The test programme will focus on effective earthing systems, and include work on:

•     Wood pole spiking for access to pole centre.
•     Characteristics of wood poles types, moisture content, and ground conditions.
•     Consideration of the different ways in which workers contact conductive parts of poles, and the different work methods used for work on poles.  
•     The effect of an earthing spike or spikes driven immediately adjacent to the pole.

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 guidance 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 workparties must focus on means to prevent inadvertent livening from occurring.