NG TS 3.05.12
Technical Specifications - Cable Tunnels
|Publication Date:||1 August 2012|
PURPOSE AND SCOPE
The specifications for new plant, equipment, apparatus and services for use on the National Grid transmission system are contained in a three-level hierarchy of documents. Level 1, TS 1, covers ratings and general requirements. The Level 2 Specifications for cable systems, TS 2.5, covers major requirements and there is a series of Level 3 Specifications covering various specific requirements.
This document is a Level 3 Specification giving the requirements for cable tunnels and relates to the initial construction and the general operation phase of the tunnel circuits. When construction or cabling works are being carried out in the tunnel (after the initial commissioning of the tunnel circuits) then a different set of circumstances will apply and specific Risk Assessments will be required with appropriate mitigation.
This document deals with the safety and reliability of cables in cable tunnels with the aim of managing risks to personnel and equipment. It is recognised that cable tunnels can be hazardous to personnel and the conditions onerous for ancillary equipment.
There are two conditions to be considered by the supplier:
a) When the tunnel is unoccupied
b) When the tunnel is occupied by staff or third parties carrying out inspections or construction work.
This means that it is advantageous to restrict personnel access to cable tunnels as much as possible throughout the tunnel lifetime and to design, plan and construct the tunnel to ensure all activities when access is required to the tunnel can be carried out in a structured manner using well maintained equipment. The risks to personnel need to be well managed and the principal ones are from fire, smoke inhalation, explosive failure of the cable and toxic gases.