Guide to Earthing and Bonding for AC Electrified Railways

The complexity of integrating the earthing of a 25kV electrified railway with various electrical distribution systems and exposed conductive parts, means that it is impossible to prescribe one earthing and bonding design solution that addresses the needs of every railway. Therefore, this creates different earthing designs for individual railways.

The guide implements a common earth system formed by bonding lineside assets and structures to the traction return system, effectively forming a low impedance meshed earth network.

The guide covers:

• Description of the AC traction electrification distribution system
• Mass of earth as part of the traction return system
• Traction return requirements and circuit configuration
• Protective provisions for humans
• Electrification system assets excluding the traction return
• Assets not forming part of the traction return
• System measurements
• Functional requirement of lightning protection for civil railway structures
• Principles of earthing at AC DC Interface
• Safe working during maintenance, renewal and decommissioning

Electrical safety is required to minimise the potential difference between all exposed conductive parts and systems sharing the system earth. This new guide explains the principles of a 'common earth' system (traction and non-traction) which is able to provide a robust and low impedance path to earth.

This guide aims to assist infrastructure owners, railway designers and installation contractors in adopting a harmonised approach towards earthing and bonding design philosophy for 25kV railway infrastructure.