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Grid infrastructureUnited KingdomEIR-0769

Cable box failure causes substation explosion and power cuts in Portishead

Nov 2023Published 15 Sept 2026Responsible editor: Chief Editor

SignificantElectrical
Estimated damageEstimated by the register's adjusterHow? Know the real figure?
Figure hidden: shown to subscribersMedium confidence
supply cut for about •• daysShown in the record →Full estimate
From the recordRoot cause hiddenFailed part hidden
Where
Electricity substation on Old Mill Road in Portishead, Somerset
Operator
National Grid
What
Cable box failure caused structural damage and wall collapse
Cause
Under investigation
Outcome
Substation to be rebuilt over nine months with temporary generators used

Companies named in the reporting of this entry (being named is not a finding of fault): National Grid

What happened

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.

Contributing factors

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.

Lessons learned

  1. A cable box failure can damage substation walls enough to need full demolition and rebuild rather than repair.
  2. Temporary generators can keep the wider network live while a damaged substation is reconfigured.
  3. Assets with no reported prior faults can still fail, so inspection regimes must not be relaxed on a clean record.

More lessons on electrical protection and isolation, maintenance, inspection and ageing assets, from every incident on the register.

Not yet known

  • Cause of the cable box failure
  • Age and model of the failed cable box
  • Cost of the rebuild and lost supply

This entry is updated when these are reported. Get an alert for the next one like it.

Source

somersetlive.co.uk

Published 2026-09-15. Written from public reporting. Descriptive, not investigative. See the data accuracy disclaimer.

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