Earth Bonding of Reinforcing CagesOn In-Service Concrete Poles: Part 3

Updated: Sep 10, 2020

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 wall connected to ferrules on the pole surface. This enables crossarms, earthwires and other pole mounted equipment to be bonded into the earthing system. The 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 reliable operating and safe working environments. 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, some companies have retrofitted their older poles with an external earthing system. This system typically consists of an external copper cable connecting the pole top hardware such as crossarms and transformers to a ground driven earthing electrode. It does not however connect into the pole reinforcing cage. While an external earthing system ensures operational integrity, worker safety issues can emerge during portable earthing. This paper overviews the development of methods to achieve a bond between the external and internal earthing systems on two designs of concrete pole.

-Wal Marshall

Full report can be downloaded below:

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