Go to content

Tunnel boring machine (TBM) power supply route

A high capacity 33 kilovolt (kV) 20 mega volt amp (MVA) cable power supply is needed at West Ruislip for the tunnel boring machines that will run between Ruislip and Old Oak Common to create the twin-bore Northolt tunnels.

Once the tunnelling is complete, the power supply will be used to power operational equipment within the tunnels. 

UK Power Networks have undertaken the work to lay the cable. The cable will remain the property of UK Power Networks and they will maintain it. 

The list of affected roads, detailed map of the route and a UK Power Networks produced a location summary will provide further information.

Power cables and health

For a 33kV underground cable, which is the type proposed for the HS2 power supply, it is expected that a magnetic field produced directly above it will be in the order of 1µT which is significantly lower than the 360µT limit given in the Code of Practice. The underground cable will not produce any external electric fields. These cables are already found in streets around Harrow and are not unusual in London and across the UK. 

The Code of Practice requires the electricity supply industry to keep records of all equipment that is known to be compliant, and this is done on the emf.info website which includes details for a 33kV underground cable. 

The Code of Practice was developed by SAGE, the Stakeholder Advisory Group on Extremely Low Frequency (ELF) EMFs. The group was made up from stakeholders representing a broad spectrum of views, including campaign groups and the cancer charity Children with Leukaemia (now known as Children with Cancer UK), as well as relevant industries, independent professional groups, academics, and the Government.