# Google Cloud London Outage Caused by PLC Misconfiguration A critical backup power failure led to a six-hour service blackout in London. - **Source:** [computerweekly.com](https://www.computerweekly.com) - **Published:** 2026-11-11 - **Topic:** [technology](https://brifing.si/c/technology) - **Original article:** - **On Brifing:** https://brifing.si/s/6ab35cab-02e1-4e0c-b6f6-58b5fdaa942c ## London Region Service Blackout Google Cloud experienced a significant service disruption in its London region that lasted for six hours. The outage rendered various cloud-based services inaccessible to users relying on this specific infrastructure. This event highlights the inherent vulnerabilities present in complex data center environments when managing critical power distribution systems during routine operations. ## PLC Misconfiguration Root Cause The primary cause of the failure was identified as a misconfiguration within a Programmable Logic Controller. This device, which manages automated industrial processes, was wired to the incorrect side of a power switch. This technical error prevented the automated backup power systems from engaging correctly when the primary grid supply failed. ## Backup Power System Failure Because the controller was improperly wired, the backup generators failed to initiate their startup sequence during the power interruption. Consequently, the facility had to rely exclusively on Uninterruptible Power Supply batteries. These batteries were never intended to sustain the entire load for an extended duration, leading to a total power loss. ## Battery Depletion and Downtime As the backup generators remained inactive due to the faulty wiring, the UPS batteries rapidly drained their stored energy. Once these batteries were fully depleted, the data center lost all power, resulting in the six-hour outage. This sequence demonstrates the critical dependency between automated control systems and physical power hardware components. ## Operational Risks in Infrastructure This incident underscores the risks associated with manual wiring and configuration tasks within high-availability data centers. Even minor errors in low-level control systems can cascade into major regional outages. Maintaining rigorous verification protocols for hardware installations is essential to prevent such failures from impacting cloud availability for enterprise customers globally. ## Redundancy System Limitations Redundancy systems are designed to provide failover protection, yet they remain susceptible to human error during maintenance or installation phases. In this London case, the redundancy mechanism itself became the point of failure. Engineers must ensure that control logic is perfectly synchronized with the physical electrical topology to maintain continuous service uptime. ## Impact on Cloud Reliability Cloud reliability depends on the seamless integration of software-defined management and physical infrastructure. When physical power systems fail to respond to software commands, the entire cloud stack becomes unreachable. This outage serves as a reminder that physical layer integrity remains a fundamental requirement for achieving high-availability targets in modern computing. ## Future Mitigation Strategies To prevent recurrence, infrastructure teams must implement stricter validation steps for all PLC wiring changes. Future mitigation will likely involve enhanced testing of failover scenarios after any hardware modification. Ensuring that backup power systems are truly isolated from configuration errors is a priority for maintaining the stability of global cloud regions. ## Sources covering this story - https://www.computerweekly.com/news/366654638/Google-Cloud-pins-London-outage-on-PLC-misconfiguration — --- _Summary written by Brifing from the original reporting. Copyright in the original article belongs to its publisher; read the full piece at the link above._