A transmission line failed near Washington, DC, this week. The grid normally recovers in seconds from such events. Recovery stretched beyond 10 minutes because over 3 gigawatts of data center demand dropped away almost instantly.

Voltage levels spiked across the PJM network from Northern Virginia to Chicago, according to measurements from Ting Labs and its network of IoT sensors installed in household outlets.

No blackout resulted, but lights flickered across the region. The episode highlighted the growing impact of data centers on grid stability, a trend experts expect to intensify.

Northern Virginia lies in PJM territory and contains the world's largest concentration of data centers.

"This acts as an early warning," Ricardo de Azevedo, CTO at ON.Energy, told TechCrunch. Events involving large loads such as data centers are "occurring with greater frequency," he noted.

The episode recalls a similar case two years ago on the same grid and may signal bigger risks ahead unless data centers manage power disruptions more smoothly. PJM Interconnection oversees grids from New Jersey to Illinois and supplies 67 million customers as the nation's largest grid operator.

The failed line prompted data centers to shift to backup power, removing about 3.1 gigawatts of load in roughly 30 seconds per PJM records. The grid began to stabilize before more loads disconnected. Peak excess reached 3.49 gigawatts, and full recovery took 11 minutes. The affected centers equaled around 3 percent of PJM demand at the time, Reuters reported.

A few percent may seem minor, yet the grid must stay nearly balanced between supply and demand. Mismatches cause voltage sags or spikes. Small variations are tolerable, but larger ones activate protective systems that disconnect equipment.

Data centers in Northern Virginia detected the voltage dip from the line failure and switched to backup, cutting their draw from the grid. As more centers followed, demand fell sharply and supply surged, causing bulbs to flicker.

Most data centers react in fractions of a second. Those involved this week behaved similarly, disconnecting within seconds of the voltage change, said Ali Zain Banatwala of the Independent Electricity System Operator.

"We must arrange for these nearby loads to disconnect or reconnect in sequence," he said. An orderly approach would let operators prepare stronger response plans.

Data centers could also be designed to tolerate disruptions instead of disconnecting. ON.Energy has created a campus-wide uninterruptible power supply that covers servers, chillers, and other systems. It places the entire facility behind batteries and advanced converters so the grid sees one steady load. The setup lets centers adjust computing loads, including AI training, without disturbing the grid.

More crucially, the system absorbs grid fluctuations. Extra power charges batteries, while dips draw from storage to keep servers running. It responds within milliseconds to prevent the sags or surges seen this week.

ON.Energy is deploying 3 gigawatts of capacity across four data center sites, de Azevedo said.

Grid operators are addressing the issue. ERCOT plans to require large loads such as data centers to ride through disruptions, de Azevedo noted.

Time is short. This week's disconnection was twice the size of a 2024 event that removed 1.5 gigawatts from 60 centers. Data centers then made up 6 percent of PJM load, per Synapse Energy Economics. By 2040 they may reach 24 percent. Without fixes, larger problems could emerge.