scope:

Applicability

This standard applies to the traction return circuit and associated earthing and bonding that form part of the a.c. electric traction energy subsystem and installations that can be endangered by the traction power system. It applies to:

a) connections to the traction return circuit of the electric traction in a.c. electrified railways;

NOTE The traction return circuit itself is part of the electric traction energy subsystem design.

b) wholly conductive or partly conductive structures or parts in the overhead contact line zone (OCLZ) and/or current collector zone (CCZ);

c) electrical installations fed by the contact line system;

d) installations that that are outside the OCLZ and outside the CCZ but which can be endangered by the traction power supply system.

The electric traction energy subsystem and the functional interfaces with the traction return circuit are outlined in Figure 1.

Earthing and bonding system interfaces 

The earthing and bonding system under consideration can be further described and structured into subsystems. The principal railway subsystems and the electrical interfaces related to earthing, bonding and the traction return circuit are described in high-level terms in BS EN 50562 and in Table 1 of this standard.

Exclusions from scope 

This standard does not apply to: 

a) matters concerning electrical safety and earthing within distribution network operator (DNO) or transmission network operator (TNO) traction supply substations; 

NOTE 1 The earthing and bonding in traction substations is covered in BS EN 61936-1, BS EN 50522, BS 7430 and ENA ER P24 (this list of standards is not exhaustive). 

NOTE 2 Where a connection to the traction return circuit is made within a traction supply substation, the touch potential limits are prescribed by BS EN 50122-1. The point of connection to the traction return system is at the return current busbar (RCBB). 

b) traction switching stations themselves other than the RCBB connection to the traction return circuit; 

c) workshops, depots, train wash facilities and similar facilities (unless they are located in the OCLZ and/or CCZ); 

d) a.c./d.c. traction interfaces; 

e) the bonding required for train detection; 

f) rolling stock, rail vehicles or plant that operate on the electric traction energy subsystem; 

g) maintenance of the traction return circuit; 

h) operational procedures. 

Purpose 

The purpose of this standard is to define the fundamental design principles that support the development of earthing and bonding system design to meet legislative requirements and to achieve safety, economy and performance. This standard acts as the requirements as obliged in: 

a) National Technical Specification Notice - Energy (ENE); 

b) BS EN 50122-1; 

c) Energy Networks Association Engineering Recommendation (ENA ER) G12; 

d) BS 7671; 

e) RIS-1855-ENE; 

and therefore, supports compliance with the Health and Safety at Work Act 1974 and the Electricity at Work Regulations 1989. 

This standard provides a common strategy to demonstrate compliance and optimise the design of railway subsystems in line with the requirements of NR/L2/ELP/27275, but is not intended to reiterate legislation and governing standards.