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When datacenters lose power, generators should kick in. That didn’t happen for Google in London

Software1 min read

Google Cloud's London data center lost power on October 20, 2026, and its backup generators did not start. A setting error in the control system was the main cause, and the outage hit several well-known banks and services.

What happened

On October 20, a cable from the power supplier broke. That cable feeds one of the two main power lines for Google's europe-west-2-b zone in London. The other power line was already turned off for repairs. Batteries (UPS) took over at first, but the on-site generators did not start. When the batteries ran out, the servers went down. Customers such as Lloyds, HSBC, Royal Mail and Revolut were affected.

Some key words

A datacenter is a building full of computer servers that run websites and apps. Its generators are backup engines that make electricity when the main grid fails. A PLC (programmable logic controller) is a small computer that controls machines, here the generator plant. Google says the PLC should have sent a start signal to the generators, but it did not.

Key facts

  • Outage date: October 20, 2026
  • UPS batteries were designed to keep things running for about five minutes
  • A planned generator load test on October 14 led to feeder B being switched off for repairs
  • Google published its explanation in a status update on November 4

Why it matters

Backup power is supposed to protect against exactly this kind of failure. This outage shows that even a large, well-prepared company can be caught out when maintenance work and a fault happen at the same time. It also shows how one small setting error in a control system can stop a whole backup plan from working.

What to watch

  • Whether Google's added testing for power problems across its platform works as planned
  • How quickly Google's new automatic alert system tells customers about problems
  • Whether other datacenter operators check how their own control systems respond when the main grid is lost

Glossary

UPS
Uninterruptible power supply: a battery system that gives short backup power when the main power fails.
PLC
Programmable logic controller: a small industrial computer that controls machines based on set rules.
Google Cloud
Google's business service that rents computing power, storage and software to other companies over the internet.

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