NR NR/L2/SIG/11201/MOD B6 ISSUE 6 PDF

This module summarises the subject of bonding & earthing of signalling equipment; bonding & earthing is required primarily:

• to protect staff against electric shock from dangerous touch potentials including those from functional signalling power supplies;

• to reduce damage as well as shock, particularly in electric traction areas, by providing a fault current path and facilitating automatic disconnection;

• to protect equipment from electrical transients and shield from interference [Electromagnet Interference, EMI];

• to provide a functional reference to allow equipment to operate (generally a heritage necessity);

• to provide a test earth (which being a separate earth will always be insulated and treated as a live conductor).

Occasionally an earth connection may be required to comply with the enforceable standards of the electricity supply industry (for ‘PME’ installations).

Particular clarity is given for all signalling equipment when earthing and bonding of the electrification system is designed to meet EN 50122-1 and which changes traditional British signalling practice. It also clarifies the requirements for the form of functional and fast transient earths. The adoption of these revised approaches will maintain safety and performance and reduce on-track time, construction effort and both initial and through-life costs.

This module applies to electrified and non-electrified railway:

• Infrastructure Projects Advice Note PAN/E&P-E/EE/ESD/0102 ‘Earthing and Bonding for AC Electrification Schemes applying Common Bonding’ initially served to describe all bonding requirements; it gave particular details for signalling equipment.

NOTE: This PAN has now lapsed with the publishing of Network Rail standard NR/L2/ELP/21085; the content of both documents are valid, but where difference exists, 21085 takes precedence. The PAN is a Reference Design under CSM-RA legislation in the meantime; this will include a module or reference of the requirements for bonding of small signalling ‘piece’ parts in the overhead contact line zone.

• In dc traction areas bespoke engineering is required

NOTE: EN 50122-1 applies and should form the basis of an engineered solution.

• Where there is a requirement for a safety earth to protect from electric shock from signalling power distribution systems, Company Standard NR/L2/SIGELP/27418 Design, Installation and Testing of Earthing in Signalling Power Systems applies however it should be understood that the preference for signalling power distribution is to adopt Class II [NR/L2/SIGELP/27410 Specification for Class II based Signalling Power Systems] or hybrid protection so that new installations minimise the requirement for a safety earth ‘at the equipment housing’ to protect against electric shock from the signalling power system.

• NR/L2/SIGELP/27418 also describes the construction design for a lineside earth and this SDH Module describes the practical minimum necessities of this ‘ground connection’ when used solely for transient and functional purposes.

Purpose and Introduction

This module forms part of the Signalling Design handbook (SDH: NR/L2/SIG/11201) and is to be read in conjunction with the other modules of the handbook and reference documentation.

This Network Rail standard contains requirements and guidance on signalling engineering applications. The content supports the specific and general requirements described in Railway Group Standards and the Network Rail Signalling Principles Handbook [NR/L2/SIG/30009].

NOTE: Where there is a conflict between this standard and a Railway Group Standard or the Network Rail Signalling Principles Handbook [NR/L2/SIG/30009] then this standard shall not take precedence

Decisions made by a competent person should be supported by appropriate evidence or documentation.

NOTE: Use of designer notes on drawings (otherwise known as Y-Notes; also see HSE CDM guidance) will generally suffice as may Design Log entries.

Any adoption of alternative solutions requires an assessment commensurate with the significance of the proposed change and which follows the guidance provided by the Common Safety Method for Risk Evaluation and Assessment [CSM-RA]; Network Rail’s adopted method for the control of safety risks.