Cable box failure causes substation explosion and power cuts in Portishead

An electricity substation on Old Mill Road in Portishead, Somerset, operated by National Grid, suffered a cable box failure just before 10pm on 29 November 2023. The failure caused structural damage to the substation walls, with part of a wall collapsing and bricks strewn around the area. Residents in the town reported power cuts and flickering lights, though National Grid stated only eight people were left without power. Temporary generators were installed at the site to keep the wider network on supply while reconfiguration took place. The substation is to be taken down and rebuilt, including replacement of the switchgear, with the rebuild expected to take around nine months. The cause of the cable box failure remained under investigation at the time of reporting.

National Grid stated there had been no previous issues with the substation and that the cause of the cable box failure was still being investigated.

1. Cable box failures can cause significant structural damage to substation buildings, requiring demolition and rebuild rather than simple repair.
2. Temporary generation can be an effective interim measure to keep the wider network on supply while a damaged substation is reconfigured or rebuilt.
3. Assets with no reported history of problems can still fail suddenly, so inspection and condition monitoring regimes should not be relaxed on the basis of a clean record.
4. Rebuild timescales measured in months should be reflected in network contingency planning.

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