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Ross-on-Wye 400kV cable replacement programme - uPVC Ducts

Ross-on-Wye 400kV cable replacement programme - uPVC Ducts

Emtelle 250mm uPVC class 1 ducts chosen for the Ross-on-Wye 400kV cable replacement programme.


For the National Grid- Western Alliance project replacing the 4x 400kV underground cable circuits from the villages of Wallford, Goodrich and Marslow, there were many areas of “Technical Difficulty”. These involved 6 road crossings including the A.40 dual carriageway, a directional drill crossing under the River Wye, a flood plain by the river, and a steep climb up to a ravine.

Owing to the critical nature of the possible cable de-rating, the cable ducts had to be laid at accurate depths and with accurate spacing of the 3 ducts of each of the 4 circuits.

Project Details

Client: National GridContract: Ross-on-Wye 400kV cable replacement and upgrade.

Contractor: Western Alliance compromising:-Amec.

Babcock International Group

Mott MacDonald

Route Length: 3.5 kilometres compromising 4 electric circuits

Cable Specification: 2,500sq/mm 400kV XPLE.

Copper core.

Start Date: May 2011

Completion: June 2016

Duct Specification Virgin polymer solid wall uPVC to BS/EN 50086-2-4250mm Black x 6mtr (750N) with integral ring-seal joints laid in 3 duct flat spaced formation for 400kV cables. At 12 metre centres were Conductive connector pieces to trace any cable/jacket fault96.5mmx6mtr (450N) with push-fit joints in:

Black for pilot and telecom fibre cables:

White for Cable & Wireless fibre cables

Critical area of technical difficulty The 4 circuits comprising 12x 250mm duct runs had to pass under the A.40 dual carriageway in a manner that allowed to ducts to remain in their optimum spacing on the horizontal plane but to within close tolerances on the vertical depth of burial plane to prevent cable de-rating.This incurred the need for specially fabricated long-radius bends to accurately match the drawings and dimension provided.These bends were then to be labelled in assembly order for each circuit and positioned on site in assembly order.
Conductive Connector Pieces The most common cause of cable jacket faults and cable damage occurs during cable placement into the ducts. These are due to the cable scraping the duct during winching as well as dirt and grit not properly cleaned out during pigging. A cable jacket fault can lead to full cable failure. Emtelle Conductive Connector Pieces comprising a similar electro-conductive coating to the cable placed at 12 metre intervals does away with that long process of elimination dig downs. Using the POPIE method sending 12kV impulses down the cable and following with a BICOTEST 12kV DC S271T MAGPIE trace set, you walk along the cable route and the impulse is picked up at the nearest “Conduct” semi-conductive joint.
Installation Process72x special 250mm diameter bends of varying radu were fabricated to accommodate the critical dimensions  shown on the drawings. Each bend had to be labelled and marked in its assembly order showing circuit number and assembly position.The bends were then delivered to site and laid out on the Haul Roads between the circuit paths in assembly order.The A.40 dual carriageway was then reduced to one carriageway, excavated, the sides shored up, and the concrete bed laid to specification.

As can be seen, the bends have accurately matched the laying profile specified by Mott MacDonald.

The process was then repeated for the parallel second carriageway lane.

On the rest of the installation, changes of direction were accommodated by the natural flexibility of the uPVC duct.

Since the 400kV copper cored XLPE cable is very stiff, all standard site bends were fabricated to 11 ¼ Degree increments on a 20 metre radius which suited both route changes and topographical changes without endangering the cable from over bending.

To date, where all 4 circuits have been cabled, by using a good quality cable lubricant, the cables have been placed with the minimum of tensile pull thus reducing the stress to the cable to the barest minimum.



Solid wall uPVC Duct made from virgin polymer from an accredited ISO 9000 & 14000 Manufacturer to 750N compression strength for High Voltage Cables. Virgin polymer gives predictable elevated temperature/compression performance, which far out-performs polymer using re-grind materials.
Extruded to withstand 750N compression at ambient temperature to BS/EN 50086-2-4 and as required for ENATS 12-24 (2008) This will give 450N compression protection to the cables out temperatures in excess of 75 degrees centigrade.
uPVC Class 1 High Voltage cable ducts are lightweight and flexible This gives the contractor a user-friendly system which is easy and effective to install.
Integral ring-seal socket joints ensure the duct being air and water-tight to IP57 and which will not pull apart. This prevents surface water and water-borne furies from entering the duct system and provides a secure joint. Further, these joints will hold during the filling of Bentonite thermal grout.
Emtelle ducts are extruded to very close production tolerances. Presenting a system that provides minimal friction for rope and cable placement.
An internal chamfer is made on all spigots of production ducts, bends and specials. Prevents cable chafing if pulled against the spigot end during cable placement.
Emtelle “Conduct” Conductive connector pieces will detect cable/jacket faults Saving time and money in accurately tracing any cable/jacket fault to the nearest conductive coupling.
  • Emtelle UK Limited have an established policy of full product commitment going back 30 years
  • On this project Emtelle UK Ltd were in dialogue with the Cable Manufacturer Prysmian Cables & Systems Ltd, and with the National Grid- Western Alliance Consultants Mott MacDonald at the earliest stage.
  • The electrical engineering/performance requirements were coordinated with the capabilities of the 400kV copper cable and Emtelle UK Ltd were then tasked with providing a ducted system with bends and specials to meet these complex demands.
  • The National Grid- Western Alliance Contractors Amec and Babcock International Ltd then organised “tool-box” talks by Emtelle UK Ltd to the site installation teams to that everyone was conversant with the products and how they were to be installed. Return visits were made to monitor progress.

For further information, please contact:

Andy Martin. UK Power Sales Manager. Emtelle UK Limited.

Phone:  07979 538967



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