Data Center Power Outage: What Grids See

A data center power outage is usually told from the inside: a UPS fails, a transfer switch sticks, a hall goes dark. Grid operators now worry about the opposite direction too — a disturbance on the transmission system that makes dozens of data centers leave the grid at once. This post covers both, using primary sources and the public records ZoningLabs has compiled on where data center buildings sit.

Key takeaways

On July 10, 2024 a 230 kV line fault in Northern Virginia led to the simultaneous loss of about 1,500 MW of data-center-type load; about 1,260 MW stayed off for hours (NERC incident review, Jan 2025).
NERC told FERC the event spanned 60 load points and 25 substations, and listed a second event: 1,800 MW lost in Loudoun and Fairfax counties in February 2025 (NERC presentation to FERC, Apr 17 2025).
Inside the fence, power is still the leading cause of impactful outages: 45% of respondents' most recent impactful outages in 2025, down from 54% in 2024 (Uptime Institute Annual Outage Analysis 2026).
Of the 927 data center buildings in the ZoningLabs facility export, 485 are in Northern Virginia — the same area as both NERC events (ZoningLabs facilities).

Two kinds of data center power outage

On-site failures. Uptime Institute's 2026 analysis says power "remains the leading cause of impactful outages", dominated by failures involving UPS systems, transfer switches and generators (Uptime Institute, 2026). That 45% figure is about equipment inside the facility, not about the utility grid failing.

Grid-side disturbances. Here the data center does exactly what it was designed to do — protect its servers — and that protective action becomes a problem for the grid. Large blocks of load vanishing in seconds push frequency and voltage the other way, and operators did not plan for it.

What happened in Northern Virginia in July 2024

NERC's incident review describes the sequence (NERC, Jan 8 2025):

At about 7:00 p.m. Eastern on July 10, 2024, a lightning arrestor failed on a 230 kV transmission line.
The line's auto-reclosing produced 6 successive faults in 82 seconds.
Customer protection logic — in NERC's words, three voltage disturbances within one minute — transferred the data centers onto backup power, where they stayed until manually switched back.
About 1,500 MW of load dropped at once. The review describes it as "exclusively data center-type load" and says the loss was "not anticipated by the BES operators".

No customer lost service: the servers ran on backup. The grid, meanwhile, suddenly had roughly 1,500 MW more generation than demand.

How regulators have responded

NERC Large Loads Task Force published Characteristics and Risks of Emerging Large Loads in July 2025 (white paper).
On May 4, 2026 NERC issued a Level 3 Essential Action Alert on computational load, with seven required actions for registered entities and a response deadline of August 3, 2026 (NERC announcement).
Texas SB 6 (2025) lets ERCOT direct a utility to have a large load customer deploy on-site backup generation or curtail during an emergency, requires curtailment equipment for new transmission-voltage large loads, and creates a competitively procured demand-reduction service for customers of at least 75 MW (SB 6 enrolled text).

How big the load is getting

Berkeley Lab estimated US data centers used 176 TWh in 2023, 4.4% of US electricity, and projected 325–580 TWh (6.7%–12.0%) by 2028 (LBNL 2024 report).
ERCOT told the Texas Senate in July 2026 that it is tracking about 474 GW of large loads seeking interconnection, about 90% of them data centers (ERCOT, Jul 29 2026). That is a request queue, not load that will be built; the same deck says about 205 GW is eligible for ERCOT's first batch study.

Where the buildings are: what ZoningLabs' own records show

ZoningLabs compiles data center building records that counties, cities and regional bodies already publish. It is a partial map of six markets, not a national census, and anyone can pull the same layers. As of the 2026-09-12 export:

Measure	Value	Source
Data center buildings	927	ZoningLabs facilities
Operational / under construction / planned	520 / 86 / 306	ZoningLabs facilities
Northern Virginia buildings	485	Loudoun County GIS (239), Prince William County (246)
Northern Virginia operational floor area	49,329,035 sq ft	ZoningLabs Northern Virginia market
Northern Virginia floor area under construction	25,684,893 sq ft	ZoningLabs Northern Virginia market
Buildings inside Virginia Electric & Power Co. territory	417	HIFLD retail service territories
Buildings inside Northern Virginia Electric Coop territory	362	same HIFLD layer

Two cautions on reading that table:

Floor area is not megawatts. No county publishes the power capacity of a building, so the export carries none.
Territory is a map overlay. A building sitting inside a utility's service territory polygon is not proof of its supply contract.

All of Virginia is inside PJM's footprint (PJM territory served), so a Northern Virginia load-loss event is a PJM operations event. PJM's current conditions are summarised on the PJM live grid page.

Distance to the grid. For the 905 buildings where a substation match was possible, the median straight-line distance to the nearest mapped substation is 905 m, and 493 buildings are within 1 km (HIFLD substations mirror). The nearest mapped substation is not necessarily the one that serves the building.

California: PG&E's large-load pipeline

PG&E publishes new-load projects queued on its distribution circuits. The ZoningLabs snapshot of 2026-09-11 holds 30,866 rows — 30,758 known and 108 pending (PG&E DRP known load layer, pending load layer; browsable at ZoningLabs large-load).

Only 11 rows are typed Datacenter: 7 ongoing, 3 new and 1 cancelled.
MONTAGUE substation carries 3 of them and RIVER OAKS 2.
Residential projects make up 18,869 rows, the bulk of the pipeline.
PG&E's expected-load field reads -99.99 on every published row. The dataset therefore shows where, what type and how far along each project is, but not how many MW. We do not estimate it.

What this means if you run or site a data center

Ride-through settings matter to the grid, not just to your uptime. NERC's review turns on a specific trigger: three voltage dips within a minute.
In Texas, SB 6 makes curtailment and backup-generation deployment during emergencies part of interconnecting a large load.
Before siting, look at the published record: county permits, utility territory, and distance to substations and transmission. The US power plant map and balancing authority map help place a site within the wider grid.

FAQ

What causes a data center power outage?

Most impactful outages trace to on-site power equipment: UPS systems, transfer switches and generators. Uptime Institute puts power at 45% of respondents' most recent impactful outages in 2025. Grid disturbances can also send a facility onto backup power, which is a data center power outage from the grid's point of view even when the servers stay up.

Did the July 2024 Virginia event black out data centers?

No. NERC's review says the data centers transferred to backup power in response to the voltage disturbances. The customers kept running; the grid lost about 1,500 MW of demand at once.

Why is a data center power outage a grid reliability problem?

When many large loads disconnect together, the system suddenly has more generation than demand. NERC's May 2026 Level 3 alert cites load reductions and oscillations that "occur in seconds, leaving little or no room for real-time responses."

How many data centers does ZoningLabs track?

The current export holds 927 buildings compiled from public county, city and regional GIS layers across six markets. It is not complete coverage of the US, and the underlying layers are public.

Does ZoningLabs have real-time data center outage alerts?

No. ZoningLabs republishes public records with their snapshot dates and source links. For live grid conditions, the operators' own dashboards are authoritative; our live grid status pages summarise them with timestamps.