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Electrical Interference on Underground Structures

Published: 20001101 by EPIC - Educational Program Innovations Center
Author(s): Robert Gummow

Interference can be defined as any electrical disturbance on a structure caused by a stray current. In this context, ‘stray’ refers to a current in an unintended path, although it is recognized that current will take all available paths in inverse proportion to the relative resistance of each available path.

Corrosion as a result of interference from a DC transit system was first reported by Stone & Forbes in 1894, just six years after the transit system began operation. Their paper was entitled ‘Electrolysis of Water Pipes’ and the term ‘electrolysis’ has persisted to denote the corrosion attack on an underground structure caused by a stray current. Regional committees of underground utility representatives that were formed to discuss mutual electrical interference problems are called Electrolysis Committees.

Sources of stray current are any AC or DC systems that are grounded to the earth or use the earth as a current path. This includes both AC and DC power systems, cathodic protection systems, electrified transit systems, and telluric currents caused by the interaction of solar particles on the earth’s magnetic field.