All new transmission strength concrete poles (and now many distribution strength poles) are manufactured with “integral earthing systems”. This means the pole is built with an earthing system within the pole connected to ferrules on the pole surface. This enables crossarms, earthwires and other pole mounted equipment to be bonded into the earthing system. The earthing system runs the length of the pole, and ensures the pole reinforcing cage and all accessories on the pole remain at a uniform potential at all times. This ensures a reliable operating and a safe working environment. However many older concrete poles were not fitted with an integral earthing system. To ensure operational reliability and prevent damage to the poles and crossarm bolts, Transpower have retrofitted their older poles with an external earthing system. This system consists of an externally mounted copper XPLE cable connecting the pole top earthwire and crossarms to a ground driven earthing electrode. It does not however connect to the pole reinforcing cage. While an external earthing system has ensured operational integrity, safety issues have emerged during portable earthing. This paper looks at methods to achieve a bond between the external and internal earthing systems.
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