scope:

This standard applies to the selection and installation of replacement power cables in existing signalling power distribution systems.

This standard specifies the equivalent modern cables sizes complying with NR/L2/SIGELP/27408 for the following legacy cables:

a) B2 and D2 cables complying with RT/E/PS/00005;

NOTE 1: D2 cables are the LSZH equivalent cables of B2 cables.

b) MD2 and D2 type cables (pre 1986 nomenclature) complying with BR 872;

NOTE 2: MD2 indicates metric sized cables and D2 indicates imperial sized cables.

c) B2 and D2 type (post 1986 nomenclature) cables complying with BR 872;

d) Twin and four-core aluminium PVC insulated armoured cables complying with BR 880; and

e) PVC insulated cables complying with BS 6346.

This standard may also be used to derive the equivalent cables, without the need for design, for the following:

a) Equivalent aluminium conductor cables for copper conductor cables;and

b) Equivalent four-core cables for two-core cables.

Exclusions

This standard is not intended to be used for wholesale cable renewals of signalling power feeder cables where electrical circuit parameters are likely to be significantly affected.

NOTE 3: Wholesale cable renewal requires design to be carried out so that current standards are satisfied.

This standard shall not be applied when undertaking system configuration changes where designs are required. Such works are subject to NR/L2/ELP/27311.

Purpose

This standard authorises, subject to constraints specified, the replacement of signalling power supply cables complying with BR 880, BR 872 or RT/E/PS/00005 with cables complying with NR/L2/SIGELP/27408.

This standard is intended to facilitate replacement of cables without resorting to design, subject to exclusions, in order to improve the availability and safety of signalling power supply systems.

This standard will mitigate against the risk of selecting inappropriately sized cables when carrying out emergency repairs or undertaking functionally equivalent replacement of existing cable sections.

NOTE: Selection of incorrectly sized cables may lead to excessive voltage drop, reduced short-circuit current capacity and increased capacitance of the signalling power supply system.