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

Google's November 4 status-page update explains the October 20 outage in its europe-west-2-b zone in London, which disrupted Lloyds, HSBC, Royal Mail and Revolut, according to The Register. A utility cable feeding primary feeder A failed while feeder B's breaker was open for repairs after a generator test. The UPSes held, but Google says a voltage-sensing design flaw and PLC misconfiguration kept the generators from starting. The account is Google's own. The lesson for operators is that redundancy gives little protection during maintenance windows when it is reduced.