Earthing and bonding of electrified railways

Electrified railways need to incorporate special earthing and bonding arrangements to meet with their own and statutory requirements on safety, touch potentials and interfaces with other trackside electrical equipment-the latter possibly fed from various other sources. While earthing and bonding principles on AC electrified railways are relatively straightforward, and the measures available are almost universally accepted, the earthing and bonding of DC electrified railways is open to controversy, various railways around the world adopting different strategies to suit their differing circumstances. On a DC railway, the situation is compounded by the requirement to keep stray currents within specified limits. The principles of stray current control in context of the earthing and bonding strategy for a DC railway system are interrelated issues, and are the principal subject of this paper.