Power outages 101

Power outages are often misunderstood. The massive blackouts that make headlines—like the one caused by Winter Storm Uri in Texas in 2021—are rare. The more common outages in your neighborhood—the ones that flicker your lights or cut power for a few hours—are usually caused by trees, animals, or aging equipment, not an overloaded Texas grid.

Understanding why outages happen can help you prepare. This guide breaks down the real causes of power disruptions, the types you’re most likely to experience, and the biggest misconceptions about the grid.

Transmission system vs. distribution system failures

To understand why power outages happen, we need to know about two systems that deliver electricity: the bulk power system and the distribution system. 

Each plays a distinct role, and the type of failure can reveal a lot about the causes of outages.

1. Transmission system (generation): This system manages large-scale electricity generation and transmits very high-voltage power over long distances using big transmission towers. Failures at this level are rare but can have widespread effects when they do occur. For example, Winter Storm Uri in Texas in 2021 caused a significant outage due to extreme cold, increased demand, and power generation shortages. However, events like this are extraordinary, occurring perhaps once in a century.
   
   
2. Distribution system (last mile): Nearly all outages—about 99%—occur within the distribution system. This low-voltage system includes the poles and wires outside your house that deliver electricity from substations to homes. These two systems connect at big substations, where high-voltage transmission lines step down power for local use. Because the distribution system is exposed to external factors like weather, vegetation, and wildlife, it is far more vulnerable to failures.

By looking at the distribution system, we find that most outages come from local hazards. These include fallen trees, animals, or old infrastructure. They do not usually result from major failures in the larger grid. 

The top causes of power outages

1. Severe weather

Weather is the number one cause of power outages, accounting for 83% of disruptions. Specific weather impacts include:

• High Winds: Storms can knock down power lines or push trees into them.
• Lightning: Direct strikes can damage equipment, while nearby strikes may overload circuits.
• Ice and Snow: Ice buildup can snap branches or topple utility poles, while snow adds weight to structures.
• Flooding and Mudslides: Water can damage underground cables and substations.
• Heat Waves: Extreme heat can stress systems, and wildfires can destroy infrastructure.

2. Trees and vegetation

Overgrown trees are another common cause. Problems arise when:

• Branches fall on power lines during storms.
• Vegetation grows too close to wires.
• Landscaping or trimming leads to accidental damage.

Utility companies regularly prune trees to reduce risks, though this sometimes creates tension with local environmental groups.

3. Wildlife

Animals often cause outages by interfering with equipment. Examples include:

• Squirrels and birds coming into contact with power lines.
• Animals nesting in substations.
• Chewing on cables.

Squirrels are especially well-known for causing power disruptions.

4. Motor vehicle accidents

Collisions with utility poles can bring down power lines, causing localized outages.

5. Equipment failure

Like any system, power grids experience wear and tear. Common issues include:

• Overheated or corroded transformers.
• Broken insulators.
• Faulty underground cables.

Maintenance helps, but older infrastructure is more prone to problems.

6. High energy demand

While increased energy use rarely causes outages, localized strain—like overloading transformers during extreme weather—can happen. Large-scale failures due to demand, such as during Winter Storm Uri, are exceptions.

7. Construction and excavation accidents

Damage to underground lines during construction or digging is another cause. Utility companies encourage people to check for buried lines before beginning projects.

8. Vandalism and theft

Intentional damage, such as theft of copper wiring, can disrupt service. These incidents, while rare, sometimes lead to widespread impacts.

9. Planned maintenance

Utilities occasionally schedule outages for system upgrades or repairs. These events are usually announced ahead of time to reduce inconvenience.

Types of power outages

Outages can generally be grouped into four types:

1. Permanent Faults: Equipment damage that requires repairs to restore power.
2. Brownouts: Temporary reductions in power to avoid overloading the grid.
3. Blackouts: Complete power loss, often requiring extensive recovery efforts.
4. Rolling Blackouts: Controlled outages used to balance supply and demand during emergencies.

Common misconceptions about power outages

Power outages are often misunderstood, leading to myths about what causes them and how they can be prevented. Here, we address three of the most common misconceptions:

Increased demand always causes outages

Reality: Most outages happen at the distribution level and are caused by local issues like weather, trees, or equipment failures—not because of demand spikes overwhelming the entire grid. When the power goes out, it’s far more likely due to a fallen tree branch or a damaged transformer than a grid-wide capacity issue.

This often raises the question: Why not just bury the lines? While undergrounding power lines can reduce some outage risks, it’s extremely expensive to install and maintain. And when a fault does occur, repairs can take days or even weeks compared to overhead lines, which are much faster to fix.

Outages are unpredictable

Reality: Outages are often linked to factors that can be anticipated, such as aging infrastructure in specific neighborhoods or weather forecasts predicting storms. By staying informed about weather conditions and the state of your local grid, you can prepare for outages before they happen.

Utilities can prevent all outages

Reality: No utility company can guarantee zero outages. Despite routine inspections, tree-trimming programs, and technology upgrades, the distribution system remains vulnerable to unpredictable factors—whether it's a squirrel chewing through wires or a severe thunderstorm knocking out power.

That said, Texas utilities are among the better performers in the U.S. when it comes to outage response and restoration. While no system is perfect, they continue to invest in improvements that help minimize disruptions and get the lights back on faster. And in the grand scheme? Texas is far ahead of most places in the world when it comes to keeping power flowing.

Preparing for power outages

While you can’t stop outages from happening in your home without a backup system, you can reduce their impact by:

• Staying informed: Monitor weather forecasts for severe conditions.
• Calling before you dig: Check for underground lines before starting projects.
• Reporting hazards: Notify your utility company about potential risks or outages.

For more specific tips on how to prepare your household for outages, read How to prepare for Texas blackouts with whole-home backup.

Understanding what causes power outages—and how they’re addressed—can help you feel more prepared. 

Some interruptions are unavoidable. However, you can take steps to stay comfortable and safe during an outage. Monitor the weather, get a home backup system, and keep the trees around your property well-maintained. These actions make a big difference.