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case study

Dartford Tunnel - TFL and Connect Plus Services

What we did

Sinewave supported TFL and Connect Plus Services in upgrading the electrical distribution system at the Dartford Tunnel as part of “Future Proofing” tunnel operations. Some 130,000 vehicles use the tunnel daily. The electrical equipment is constantly in use.

The Technicals
  • Replacing four 11kV/400V oil-filled transformers
  • Obtaining RAMS and lifting plan approvals from Connect Plus Services
  • Replacing HV cabling utilising existing cable routes
  • Replacing bitumen-filled cable boxes with air-insulated termination kits
  • Safely removing and disposing of oil and bitumen
  • 150 meters of HV cable installation
  • Insulation and resistance-testing new transformers and HV cabling
  • Re-energising the system
"Neil and his team produced a fine job on time and to budget"



Sinewave replaced four 11kV/400V oil-filled transformers, replaced HV cabling using existing cable routes in confined spaces, replaced bitumen-filled cable boxes with air-insulated termination kits, and performed insulation and resistance testing of the new transformers and HV cabling before re-energising the system. All environmental recycling was carried out to UK standards.


The Dartford Tunnel, now part of the M25, has been in operation since 1963. Its electrical distribution system was “time-expired.” All electrical upgrades were performed with no disruption in service. Now, the tunnel is ready to serve the motoring public for the foreseeable future.

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