Corporate

Causes of Outages

Power outages can be triggered by many conditions or circumstances. Weather is the leading cause, such as strong winds, lightning and ice storms. However, people and animals can also cause power outages.

Select a topic below for more details on the causes of power outages.

Lightning

Lightning often strikes transmission line towers, utility poles, wires, transformers and other electrical equipment, causing severe damage and loss of power.

Lightning is attracted to the most direct path to the ground and usually searches for the highest object to serve as a conductor. Trees struck by lightning may also fall on lines, causing an outage.

Wind

Strong winds can swing some power lines together and trigger a short circuit. Winds also blow tree limbs or entire trees onto power lines. Severe winds, such as those produced by hurricanes and tornadoes, can destroy extensive sections of lines and utility poles.

Ice and Snow

Ice (from freezing rain or sleet) can build up on power lines and eventually cause them to break due to the excessive weight. Many tree limbs also become heavy with snow and ice, and they eventually break and can fall into power lines. 

Water

Water can trigger power outages by damaging overhead and underground electrical equipment. Swollen rivers and creeks, flash floods and other conditions may occur following heavy rain, hurricanes, melting snow, etc. 

Coastal Salt Contamination

Salt contamination can occur on power systems that have a significant coastal exposure when winds deposit sea salt on power line insulators.  The combination of salt and moisture can conduct electricity across insulators and cause equipment to fail.

Cable Failure

Underground cable failures may occur due to construction accidents, design or material flaws, or other unusual conditions.

Tip:  Call before you dig to avoid cable failures resulting from excavation.   

Vehicles

Traffic accidents involving utility poles are a common cause of power outages. Poles may be severely damaged, causing power lines to touch objects or collapse. 

Animals

Animals periodically cause power outages by climbing onto or inside energized equipment. They can cause a short circuit that interrupts the flow of power to customers.

Trees and Limbs

Trees and tree limbs are a major cause of outages. They can fall on power lines regardless of weather conditions, and in some cases may destroy a span of lines and tear down supporting structures.

Momentary Outages

Momentary outages are generally described as a flickering or dimming of lights or a very brief loss of power. These are usually caused by short circuits when something like a tree limb comes into contact with a power line or when lines touch each other.

Electrical equipment is designed to quickly and automatically open and close the breaker two or three times in an attempt to clear the problem. For example, this will usually restore power when a tree limb blows onto a line then falls away.

If the problem does not clear itself, Dominion dispatches personnel to find the source of the problem and clear the line.

Reliability  What do causes and types of outages, storm preparation and even tree trimming have in common? They all contribute to our service reliability efforts! Whenever you see this icon, we are sharing information with you about our efforts to provide you with safe & reliable service every day of the year.
NYSE : (April 17, 2014) D 70.67 -0.86