Descending a ladder on the side of the gorge, each year a small number of lucky visitors are able to enter and explore the Leigh Woods Vaults – one of the oldest parts of the Clifton Suspension Bridge designed and built under the supervision of Isambard Kingdom Brunel. The impressive chambers inside feel like an underground cathedral; huge echoing spaces with high ceilings festooned with stalactites.
Although the environment remains free from bats and insect life, it’s common to hear the sound of water dripping as rain gradually makes its way through the structure on its way to the bedrock. Despite remaining a cool and steady 12 degrees all year round, the chambers are high in humidity and the environment is damp even when the summer sun blazes in the sky. Lighting large spaces in such conditions can therefore be challenging.
In late summer 2023, the Trust began a project to replace and upgrade the lighting systems to better show off the architecture for visitors. Over time the existing electricity supply to the vaults had degraded, to the extent that there was not even enough capacity to operate all the lights. However, fixing this was far from straightforward. The first step was to identify an electricity supply with the capacity needed – and this required rerouting exising power supplies for buildings on the surface level. A trench for the new supply was created by Chew Valley Construction, whilst electricians AMP carried out the electrical work to switch the supplies over.
Having made the supply available, the next step was to get it into the vaults. Scaffolders Triple J built a platform on the side of the gorge, then drilling specialists Ibex used this to bore a 38mm diameter hole almost 2 metres through the thick exterior wall of Vault No. 4. This required some heavy-duty drilling equipment, particularly as the hole was angled to slope gently down toward the outside of the wall to stop water making its way though into the chamber!
The new system has been created using components suitable for outdoor use, and the wiring insulation selected to be thick and robust enough to protect the internal copper from moisture. Where the wires terminate at a junction box or light fitting, there is always a risk that moisture could get in. All connections, fittings and ancillaries used therefore meet at least IP 65 (an Internal Protection rating which indicates that the component gives protection against low pressure water jets from any direction, as well as condensation and water spray). It’s suitable for most outdoor enclosures that won’t encounter extreme weather such as flooding.
As an added benefit of the project, we gained a core sample providing us with further evidence of the construction process for the vaults. It seems as though an ‘aggregate’ of coke or coal has been interspersed with the stonework. Further tests to establish exactly what the constituents are are now needed.
Once AMP ran the new cable into position and made all the internal connections the vaults once again became fully illuminated. We now not only have brand new lighting in place for the 2024 season – but we also have spare capacity for any future projects!