I thought the electricity cables ran through one of the old single-track tunnels. There are three bores in total.
After several bouts of agitation and a bit of shouting over many years, new cables were installed in the 1953 tunnel during 2008-2012. If you look at Dunford Bridge on Google Earth you can see the works site at that portal in the historical imagery - there doesn't seem to be much now to show it.
At the time of their completion in 1845, the two Victorian tunnels were among the world's longest railway tunnels. British Rail added a third tunnel in 1953. The Victorian tunnels were acquired by the CEGB in the 1960s to carry the trans-Pennine 400-kV electricity link below ground, rather than over the moors of the Peak District National Park.
It is not possible to install new electricity cables alongside the existing cables in the Victorian tunnels for two reasons:
Firstly, to ensure continued safe and secure electricity supplies for Greater Manchester, the existing cables need to remain in service while new cables are installed. Because of the confined space, there is not enough room to carry out major engineering works to install new cables in the tunnels alongside the existing "live" 400-kV cables.
Secondly, despite a great deal of maintenance work over the years, the condition of the Victorian tunnels has continued to deteriorate and they would require considerable civil engineering works at substantial additional cost to be made safe for long-term use for any purpose.
Therefore the replacement cable circuits will be installed in the third, more modern, Woodhead Tunnel. This tunnel was closed in 1982 and was bought by National Grid in the early 1990s with this purpose in mind. This project forms part of National Grid’s ongoing national investment program and represents a significant investment in the region’s power network.
The new cables are being installed in the 1953 tunnel, via the entrance at Dunford Bridge, by the Electricity Alliance - East on behalf of National Grid.
(From
here, written in 2008.)