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Power outages can be caused by many circumstances. Storms, when they are accompanied by heavy wind and
lightning, are major causes of power outages. However, people and animals can also cause the power to
go out.
Lightning
Lightning looks for the quickest path to the ground. It generally searches for the tallest object to serve
as a conductor. Utility poles, wires, transformers and other electrical equipment are easy targets for
lightning strikes, causing severe damage and loss of power. Lightning also frequently strikes trees causing
tree limbs or even large trees to fall onto utility lines.
Wind
Wind may cause power lines to swing together resulting in a fault or short circuit that interrupts service.
Strong wind can blow tree limbs or entire trees into power lines causing them to fall to the ground.
Severe winds can even break power lines and utility poles, bringing down extensive portions of the infrastructure
that delivers power.
Snow and Ice
Winter storms are a threat to electrical equipment when snow and ice build up on power lines and tree limbs.
The weight of the snow and ice can cause wires to break. Tree limbs also become heavy with snow and ice
causing them to break and fall into power lines.
Rain and Flooding
Heavy rain and melting snow can cause flooding in some areas. Flooding can damage both overhead and
underground electrical equipment.
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Vehicle Accidents
Vehicles coming into contact with utility poles are a common cause of power outages. In an average year,
more than 900 utility poles on Duquesne Light’s system are damaged by traffic accidents.
Small Animals
Small animals can cause power outages. When animals climb on equipment, such as transformers or fuses,
they can cause a short circuit interrupting the flow of power.
Trees
Trees falling on power lines or tree limbs coming into contact with power lines are frequent causes of
power outages, even in good weather. Tree damage is the second most common cause of power outages.
Only major storms create more customer outages on Duquesne Light’s system.
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Momentary outages, which customers see as a dimming or flickering of their lights or even a brief loss of
power, are caused by short circuits. Short circuits happen when something, such as a tree limb, comes into
contact with power lines or when the lines touch each other.
When a short circuit occurs, a safety device called a breaker automatically de-energizes the circuit and
interrupts the flow of power. Electrical equipment is designed to quickly open and close the breaker two
or three times automatically attempting the clear the problem. This is the case when a tree limb blows
into a line and then swings clear.
Approximately 30 percent of short circuits clear themselves. If the problem does not clear itself, we
send a Trouble Investigator out to locate the source of the problem and clear the line.
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