Control of stray currents for DC traction systems

On a DC electrified railway system, low resistance between the traction return rails and the ground allows a significant part of the return current to leak into the ground. This is normally referred to as leakage current or stray current. The problems of these stray currents are briefly discussed and measures to combat them described. These include: maintaining rail-to-ground insulation, so far as is consistent with touch voltage requirements; implementing an effective earthing and bonding strategy-connect all rails in parallel, with adequate rail continuity bonding and cross-track bonding; installing a stray current collection system where appropriate; selecting a running rail that provides a low-resistance path for the traction return current; spacing the feeding substations at short distances; isolating all structural steelwork from the track-in particular from the under-track collection system when this is used; and ensuring effective drainage of water from the track, whether slab track or ballasted track