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Understanding and Preparing for Outages

Outage Causes

Outages may last a few seconds or a few days, depending upon the cause.  The most common causes of power outages are: natural causes, human error, and equipment failure.  There are also occasions when maintenance will result in an outage.

Natural Causes

Strong storms can cause trees or branches to fall and tear down power lines; tree limbs brushing or resting on lines can cause short circuits and blown fuses. Lightning strikes can damage substations, power lines and equipment. High winds, heavy rain, snow and ice also can damage equipment and cause outages.


There are several reasons why high temperatures can cause outages.

  • There is also the possibility of scattered outages resulting from equipment overheating. Transformers, for example, can fail from overheating. Transformers are built to dissipate their heat, but in extreme weather conditions such as we're experiencing, there is no ability to cool because temperatures remain high throughout the night. Problems are also magnified in the confined spaces of an underground electrical system. For example, if there is a flaw or crack in the cable insulation, a short circuit could occur as the cables expand from the heat.
  • Increased demand for air conditioning means more electricity flowing through power lines. This causes them to heat up and expand or sag, and in some cases they sag into tree branches, causing a short circuit.
  • Electricity loads combined with high temperatures cause transformers to heat up, sometimes reaching critical levels that if uncorrected would permanently damage the equipment. The equipment will automatically and safely shut down to protect itself and other equipment.
  • High current causes stretching of cables, switches and other equipment and can increase the size of minor flaws in insulation or connections.
  • Electric equipment can be weakened by lightning strikes and circuit failures, making it more susceptible to an outage as it can no longer withstand the increased flow of electricity during periods of high demand.

Small animals, like squirrels, sometimes chew into lines or come into contact with a piece of equipment and an energized line, resulting in their untimely demise, and an interruption of electric service for you.

Human Error

Digging a foot or two in the wrong direction can damage underground power lines, causing an immediate outage or contributing to an outage that occurs days, weeks or months later. Hitting a power line can also result in serious injury.

Before digging anywhere, call Miss Utility for locations in Maryland or District One Call in the District of Columbia at least 48 hours before all digging or construction. These companies mark the ground where utility lines are present. This service is free and notification is required by many local jurisdictions. Failure to call before you dig may result in criminal or civil penalties.

  • Miss Utility: 811 or 1-800-257-7777 (Maryland locations)
  • District One Call:  202-265-7177 (District of Columbia locations)

Vehicle Accidents
Vehicle collosions with utility poles or equipment can also cause outages.  These outages can be frustrating for residents who may live some distance away and are unaware of the cause.

Metallic balloons that are released into the air can drift into power lines or electrical equipment and cause power outages.

Equipment Failures
Just like with your car, in spite of regular service, mechanical systems do break down occasionally. The same is true of even the best-maintained electrical distribution and transmission system.

Momentary Outages

A power outage is inconvenient, whether it lasts a second or an hour. But there is a difference between a prolonged power outage and a brief, momentary interruption.

"Momentaries" are split-second interruptions in service. They are an unavoidable part of power delivery systems that have always occurred. Today's sophisticated computers and other electronic equipment are super-sensitive, however, and can be affected by a momentary that lasts only one eight-thousandth of a second.

While annoying, momentaries serve an important purpose. For example, when a tree limb falls on a wire, Pepco's automatic sensing equipment detects a potentially dangerous condition and temporarily breaks the flow of electricity protecting essential parts of our delivery system from major damage. Nevertheless, power may be out just long enough that equipment in your home, like your VCR or microwave, needs reprogramming when you return home.

Preventing Outages

What is Pepco doing to reduce the incidence of outages?

  • We prune trees along our power lines on a regular cycle to help prevent them from damaging or blowing into our power lines.
  • We use special insulated wire in heavily wooded areas that can better resist damage from falling tree limbs.
  • Lightning arresters are in place to provide a harmless path to the ground for electrical surges.
  • We use grounded shield wire above some power lines that acts as a shield from lightning strikes.
  • We install animal guards around our field equipment to protect against short circuits caused by animals.
  • We continually upgrade our facilities to keep pace with growth in our area and enhance reliability.

Preparing for Outages

Make a Plan and Assemble a Kit

Assemble an Emergency Storm Kit

Keep these items on hand:

  • Flashlights and fresh batteries
  • Battery-powered radio or television and extra batteries
  • Land line phone with cord (Cordless phones require electricity to operate)
  • Land line phone (cordless phones require electricity to operate)
  • Battery-powered or windup alarm clock
  • A supply of bottled water (one gallon per person per day)
  • Non-perishable foods that require no heating
  • Blankets, bedding, or sleeping bags and a change of clothes
  • First Aid Kit and prescription medications
  • Hand-operated can opener
  • Special items for infants, the elderly or family members with special needs
  • Hand tools such as a hammer, screwdriver; scissors; duct tape; plastic garbage bags; paper and pencil; waterproof matches; household bleach
  • Identification and copies of important family documents in a waterproof container
  • Emergency Services and Pepco telephone numbers

Collect and store these items ahead of time in order to save valuable time and to be prepared in the event of a wide variety of potential emergencies. Check the links under Additional Resources to our Federal, State and local Emergency Management Agency partners for additional information on preparations for potential emergencies.

Protect Your Food

  • Stock up on shelf-stable foods such as canned goods, juices, peanut butter, "power" bars, trail mixes and "no-freeze" entrees.
  • Plan ahead how you can keep foods cold. Buy some freeze-pak inserts and keep them frozen. Buy a cooler. Freeze water in plastic jugs or containers or store bags of ice.
  • Know in advance where you can buy dry and block ice.
  • Develop emergency freezer-sharing plans with friends in another part of town or in a nearby area.
  • Keep freezer and refrigerator doors closed; open them only when absolutely necessary.  Food will stay frozen for 36-48 hours in a fully loaded freezer if you keep the door closed.
  • A half-full freezer will generally keep food frozen for 24 hours. If you have time in advance of the storm, fill up your freezer by filling plastic bottles with water and freezing them.

Protect Electronic Equipment

  • Purchase electronic equipment with built-in protection or a battery-powered back-up system.
  • Use electrical surge suppressors or arresters on all sensitive electronic equipment. Most are designed to be plugged into a wall outlet.
  • Plug computers and other sensitive electronic equipment into a separate, grounded circuit to isolate them from fluctuations caused when a major appliance starts, such as a room air conditioner or refrigerator.
  • Consider a UPS (uninterruptible power supply) for temporary battery back-up power for sensitive electronic equipment.
  • Consider having a lightning arrester installed at your main circuit panel. This generally requires the services of a licensed electrician.

Stay Alert for Downed Lines

  • If you see a downed power line, let Pepco know immediately by calling 1-877-PEPCO-62. Stay away from any downed line. Assume it's live and dangerous, and warn children to stay away and notify an adult. Downed lines do not always spark, burn or arc. Never assume any downed wire is harmless. Objects such as metal fences and water in contact with power lines could be energized and lethal. STAY AWAY.

Protect Your Home and Belongings

  • Turn off all appliances, including your furnace, air conditioner, water heater and water pump. That way, you can avoid a circuit overload and another outage that may result when power is restored to all appliances at once.
  • Leave on one lamp so you'll know that the power has been restored.

Winter Outages

Anticipate Possible Service Interruptions

High winds, heavy snow and icy conditions can result in downed power lines or cause vehicle collisions with utility poles that may lead to temporary service outages for some Pepco customers.

Stay Comfortable and Safe

  • Gather in a central room where you have alternative heat. At night, cover windows with drapes or blankets to minimize heat loss. During the day, open blinds to let sun warm the space.
  • Dress in loose layers.
  • If the indoor temperature drops to 55 degrees Fahrenheit or below, open your faucets slightly so they constantly drip to prevent pipes from freezing.
  • If candles and heaters are used: never leave them unattended, and watch children and pets who could knock them over.
  • Avoid alcoholic beverages, which can increase loss of body heat and increase the risk of hypothermia. Do not hesitate to contact a physician if you have a health-related question.

Heating Safety

  • A fuel-burning heater, such as a kerosene heater, requires proper ventilation to prevent buildup of harmful fumes. Place heaters on a hard, noncombustible surface.
  • Never leave children or pets alone with a portable heater in use.
  • Never use gasoline or other flammable liquids to start or quicken a fire. Always keep a screen around an open flame and don't close the damper while ashes are still hot.
  • Never use a gas range for room heating.
  • Never use charcoal as an indoor heating or cooking source.

Clear Snow from Outdoor Vents

Pepco urges customers to clear snow away from appliance vents located outside their residences. This will help ensure the proper operation of heaters, water heaters, natural gas fireplaces, clothes dryers and gas and electric meters.

Snow accumulation could potentially hamper the proper and safe operation of direct-vent appliances that expel products of combustion (such as carbon monoxide) to the outdoors. Many modern homes have high-efficiency heaters and water heaters with exterior vents placed only 12 inches above the ground. All vented appliances require an uninterrupted supply of fresh air and a clear exhaust path in order to work properly and safely. Blowing and drifting snow can block the intake and exhaust vents, forcing appliances to automatically shut down and possibly causing serious damage.

Most appliances have automatic shut-offs that may indicate a problem with the venting system. If you are experiencing problems with direct-vent equipment or appliances, check to be sure exhaust vents are clear.

Use Caution During Snow Removal

Before you begin snow removal, carefully clear any accumulated snow from gas and electric facilities, propane and oil tank storage areas, and other phone, cable or utility facilities. Examples of equipment that should be cleared and marked include: meters, valves, regulators, piping and other facilities above ground that could possibly be hit by mechanized equipment or hand-shoveling. These areas should also be clearly marked to alert snow removal operators of their location.

As an added precaution, any snow surrounding fire hydrants or fire-fighting equipment should also be cleared and identified.

Summer Outages

Hot Weather Safety

The following general information is offered as a public service to help Pepco customers stay safe and healthy during hot weather. For specific information on the identification, avoidance and treatment of heat stress, please consult a licensed health care professional.

Heat stress can occur when excess heat places abnormal strain on the body. Temperature, humidity, radiant heat and air velocity affect the amount of heat stress you face. How each individual reacts to heat is affected by age, weight, fitness, medical condition and acclimatization to the heat.

Your body reacts to heat by circulating blood and raising your skin's temperature; excess heat is then released through the skin. Physical activity can raise the body's core temperature by limiting the amount of blood that flows to the skin to release heat.

Sweating also releases heat to maintain a stable body temperature if the humidity level in the air is low enough to permit evaporation, and if fluids and salts are adequately replaced.

Heat that cannot be released by the body is stored. This raises core body temperature and heart rate, potentially putting your health at risk.

Heat cramps can occur in tired muscles if you drink large quantities of water but fail to replace the body's salt. To relieve cramps, drink sports beverages or other electrolyte and salt replacers.

Heat exhaustion may develop when fluids and salt that are lost through sweating are not replaced. Primary symptoms include extreme weakness, fatigue, giddiness, nausea or a headache; other symptoms may include clammy or moist skin, a pale or flushed complexion and a slightly higher-than-normal body temperature. Someone experiencing heat exhaustion should rest in a cooler place, with the feet raised and tight clothing loosened, and slowly drink salted liquids. Heat exhaustion may rapidly turn into heat stroke, a potentially fatal condition. If symptoms persist or worsen, seek immediate medical attention.

Heat stroke is a serious and potentially fatal condition that requires immediate medical attention. Heat stroke occurs when the body's heat-regulating system breaks down, sweating stops, and body temperature rises significantly.

Signs of heat stroke include:

  • Mental confusion, delirium, chills, dizziness, loss of consciousness, convulsions or coma
  • A body temperature of 105 degrees F or higher
  • Hot, dry skin that may be red, mottled or bluish
  • A strong, fast pulse

If you suspect someone is suffering from heat stroke, call an ambulance immediately. Until medical help arrives, move the victim from the heat and into a cool place, soak the victim's clothes with water and use a fan or ice packs.

Protect Yourself From Heat Stress: Stay Comfortable and Safe

  • Close all drapes/blinds on the sunny side of the house.
  • Remember to drink plenty of fluids. During the warmer, daytime hours go to air-conditioned malls, libraries, movie theaters or any public place that is air conditioned.
  • If a family member appears overheated, use cool compresses to cool skin. Do not hesitate to contact a physician if you have a health-related question.
  • Remember to check on elderly or home-bound neighbors, who may be susceptible to the effects of heat stress.
  • Spend as much time as you can in cool surroundings. Use fans and air conditioners to cool your home.
  • Slow down and take it easy. Physical activity produces extra body heat.
  • Wear light-weight, light-colored, loose-fitting clothing made of a breathable fabric, such as cotton.
  • Wear a hat or use an umbrella to protect your head and neck when you are outdoors.
  • Drink plenty of water; don't wait until you are thirsty. By then, you may already be dehydrated.
  • Watch what you eat. Avoid eating hot foods or heavy meals. Use your stove as little as possible (use a microwave instead) and cook during the coolest part of the day.
  • Take cool baths or showers. Cool water can remove body heat 25 times faster than cool air.
  • Avoid drinking alcohol and soda, as these actually dehydrate you faster. Instead, drink water or sports drinks.

Using a Generator

Safety Tips

If you plan to use a portable generator during power outages, here are some important safety precautions:

  • Always follow the manufacturer's instructions when using a generator.
  • Locate your generator in a well-ventilated area. Never run it inside, even in your garage. Gasoline powered generators produce carbon monoxide and the fumes can be deadly. Store gasoline or other flammable liquids outside of living areas in properly marked approved containers. They should also not be stored in a garage if a fuel-burning appliance is located there.
  • Plug appliances directly into the generator using heavy duty, properly grounded extension cords. Make sure extension cords are not frayed or worn.
  • Use the generator only when necessary, and don't overload it. Turn it off at night while you sleep and when you are away from home, to avoid possible fire hazard.
  • For your safety and the safety of Pepco employees working to restore power, do not connect your generator directly into your home's main fuse box or circuit panel. Improperly connected generators can feed electricity back into the electrical system, endangering field personnel working to restore your power. Consult a qualified electrical contractor if a permanent generator installation is desired.