For a computer, a second without power is a long time. Unsaved work is lost, jobs crash and equipment can be stressed. So data centres are built never to see that second: a bank of batteries, called an uninterruptible power supply or UPS, takes over instantly, and generators start up to carry the load for longer. That protects the computers. But it has a new side effect. When many data centres in the same place all switch to their own backup at the same moment, the grid suddenly loses a very large customer, and that can upset the grid.
Inside the data centre: never drop the load
Power reaches the computers through a chain. The US Department of Energy's best practice guide, written by NREL, describes power distribution units that pass conditioned power that is sourced from a UPS or generator, and notes that the critical nature of data center loads elevates many design criteria, with redundancy requiring particular design attention. The Department of Energy's purchasing guidance explains that UPS designs differ in how much protection they give: the highest grades offer the highest level of protection for downstream equipment, and higher levels of power conditioning generally result in lower UPS system efficiency.
| Layer | What it does | Why it matters |
|---|---|---|
| Grid supply | Normal source of power | Can dip, flicker or fail |
| UPS batteries | Take over instantly when supply falters | Bridge the gap so computers never notice |
| Backup generators | Start and carry the load for longer outages | Keep the site running for hours or days |
| Redundant paths | Duplicate equipment so one failure does not stop the site | Allow maintenance and failures without an outage |
Outside the data centre: a new kind of grid event
On 10 July 2024, a lightning arrestor failed on a 230 kV transmission line in Virginia, in the United States. The North American Electric Reliability Corporation, NERC, reports that the fault led to the customer-initiated simultaneous loss of approximately 1,500 MW of voltage-sensitive load, and that the load was exclusively data center-type load. The data centres had done what they were designed to do: they transferred their loads to their backup power systems. About 1,260 MW did not return to the grid for hours.
NERC has since reported further events of this kind, and in September 2026 noted that a load reduction of nearly 4 GW in Virginia in July 2026 was still being analysed. It has issued alerts to grid operators, citing the sensitive ride-through characteristics of large data center loads, and has been directed by the US regulator to complete standards for large loads by the end of 2026.
Why it matters
A grid is balanced second by second. Losing a large demand suddenly is as much a disturbance as losing a large power station. The fix lies on both sides: data centres setting their equipment to ride through brief dips rather than leave the grid at the first flicker, and grid operators planning for how these loads behave. NERC's own recommendation after the 2024 event was to take into consideration the potential for voltage-sensitive load loss when configuring automatic reclosing schemes on transmission lines.
What is not certain
- How long UPS batteries and generators carry a site differs by design; this article gives no typical times because none was found in an official source.
- The grid events described are from one region of the United States; their lessons apply elsewhere but the details differ.
- Standards for how large loads must behave on the grid were still being written in 2026.
Sources and method
- North American Electric Reliability Corporation, Incident Review: Considering Simultaneous Voltage-Sensitive Load Reduction, 8 January 2025. https://nerc.com/pa/rrm/ea/Documents/Incident_Review_Large_Load_Loss.pdf
- North American Electric Reliability Corporation, Reliability Insights: Large Computational Load Risks Due to Voltage Sensitivity, September 2026. https://www.nerc.com/globalassets/who-we-are/news/2026/09/reliability-insights_large-computational-load-risks-due-to-voltage-sensitivity.pdf
- Midwest Reliability Organization, NERC issues critical reliability alert as emerging large loads challenge the grid, 2026. https://www.mro.net/nerc-issues-critical-reliability-alert-as-emerging-large-loads-challenge-the-grid/
- Van Geet and Sickinger, NREL, for the US Department of Energy Federal Energy Management Program. Best Practices Guide for Energy-Efficient Data Center Design, revised July 2024. https://www.energy.gov/sites/default/files/2024-07/best-practice-guide-data-center-design_0.pdf
- US Department of Energy, Federal Energy Management Program, Purchasing Energy-Efficient Uninterruptible Power Supplies, updated December 2024. https://www.energy.gov/eere/femp/covered-product-category-uninterruptible-power-supplies
Method: each link was opened on 29 October 2026 and every figure was taken from the page cited beside it. No figure was estimated.
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This article provides general information, not investment advice or an offer of securities.