What Causes Mass Power Outages?

Published on 06/25/2021

As Americans, we have grown comfortable in the knowledge that when we flip a light switch, it will turn on. We use electricity every day to power our homes and businesses and we expect it to be there when we need it. That’s because our electric grid is an amazing piece of infrastructure. Composed of over 450,000 miles of high voltage transmission lines, it provides reliable power to over 140 million residential and commercial customers.

However, there are some instances in which power becomes unavailable. In fact, outages occur quite often, but these are typically managed in under an hour and/or only affect a few customers, so they don’t make headline news. This past year, however, we saw our Eastern, Western, and Texas grids hit by several weather events that caused major disruption across the nation.

Changing climate conditions are causing spikes in the demand for electricity, and in the summer of 2020 this caused mass outages in California and other areas in the south and west. That winter, Winter Storm Uri blanketed the nation, posing extreme difficulties for grid operators around the country, but particularly in Texas where over 70% of customers lost power for an average of 42 hours.

With more mass power outages occurring, it is critical that we take a closer look at the causes of these events and determine what can be — and is being — done about them.

What Are Mass Power Outages?

Before we investigate the reasons mass power outages happen, let’s take a moment to define what exactly we mean by a mass power outage. Typically, events of this magnitude are unplanned and must:
  • Affect at least a thousand people
  • Last at least an hour
  • Cause at least one million person-hours of disruption
For example, if 900 people lost power for 60 days, that would still not be considered a mass power outage, since it doesn’t meet the thousand person threshold.

Some of the Most Widespread Power Outages in History and Their Causes
As demand for power has grown, the United States has seen more frequent power outages as the decades have gone by. In fact, since the early 80s there have been several events each year that have qualified as mass power outages. By taking a look at some of the worst of them, we can quickly see what the common denominators are:

1. Lightning in New York City 1977
When a lightning strike took down a Hudson River substation, the circuit breakers tripped to divert power. More lightning strikes took New York’s largest generator down and many neighborhoods went dark.

2. Winds on the West Coast 1982
In the winter, high winds pushed a transmission tower into a line tower causing a series of other towers to fail. More than 2 million customers from California to Nevada went without electricity.

3. Hot Weather in Western North America (1996)
Two blackouts caused by high demand during hot summer months affected millions of people from western Canada and the U.S. to northwestern Mexico for several hours.

4. Untrimmed Trees in the Northeast (2003)
In the second largest power outage in U.S. history, this outage affected eight states and 45 million people. When a transmission line impacted untrimmed trees, an alarm set to warn maintenance workers failed to sound and the issue spiraled out of control.

5. Storms in the Mid-Atlantic and Midwest (2012)
A derecho storm marked by long-lasting hurricane force winds, flash floods, and tornadoes raged through the central and eastern states, causing widespread damage and leaving 4.2 million people without power for up to 10 days.

6. Hurricane Sandy (2012)
Twenty-four states were left powerless by Sandy, with some going without electricity for up to two weeks.

As you can see, the common elements in these severe outages include storms, extreme temperatures, and uncleared vegetation. Although trees were only mentioned in one of our examples, untrimmed vegetation is the second most common cause of all power outages. Coupled with high winds, rain, ice, or snow, trees and other vegetation can pose a significant risk to transmission lines and power continuity.

What Are We Doing About Mass Power Outages?

Our nation’s power grids ensure electricity is available to missions and homes and businesses through our complex network of distribution and transmission lines. But as you can see from the examples above, although there are a number of factors that can contribute to an outage, the most common is weather based — wind, ice, snow, rain. High demand for power caused by extreme heat or cold can also be grouped here. And, as the world changes, our infrastructure also becomes more vulnerable to cyberattacks, which could lead to outage events on a massive scale.

To keep our power flowing, the U.S. government has launched a $100 billion infrastructure plan that will help renew our grid system, including laying new transmission lines and including clean energy initiatives. These new lines, coupled with renewable energy, will strengthen operations against extreme weather and add capacity to meet the growing demand.

In addition, the Biden administration has set aside money to enhance the grid’s cybersecurity protections to reduce the threat of shut-down by cybercriminals. On a local level, utilities are doing what they do best — keeping lines maintained and clearing vegetation that can pose a hazard during good weather and bad.