Power quality

Sometimes, interference in the supply of electricity affects how your equipment runs. Many newer appliances such as personal computers, microwave ovens and sophisticated stereo systems have sensitive electronics and are susceptible to disruption or damage.


From our plant to your home

PG&E operates an extensive, sophisticated power system that supplies most of northern and central California with electricity. This system delivers a reliable supply of power that satisfies national voltage standards. But occasionally, electric systems experience voltage disturbances from natural or man-made causes (e.g., lightning, wind, cars hitting power poles) for which PG&E isn't responsible. These disturbances can interfere with your appliances and even damage some of your more sensitive equipment such as computers. Fortunately, you can use devices to protect this equipment.


Types of disturbance



An interruption is a complete power loss, which can last a second or several hours. Equipment failure or damage to power lines from lightning, strong winds, falling tree branches, animal contact or car accidents can cause interruptions. These outages can affect the power to one home, one street or an entire town.

There are momentary and sustained interruptions. Momentary interruptions are more common and can happen six to 12 times a year. Most utility companies such as PG&E have devices to keep these interruptions temporary, clearing them within a few seconds. The most noticeable result of a momentary interruption is a blinking digital clock. Sustained interruptions typically last between 30 minutes to several hours. They occur less often, once or twice a year. A UPS/battery backup helps protect you against a complete loss of power.


Short-term variations

Short-term variations, known as sags and swells, can last milliseconds and create a drain on your power. You may notice these drains when the lights dim as the refrigerator starts, but usually you won't notice them. Large loads (refrigerator, washer or dryer) turning on or off can trigger swells and sags. The circuit supplying power to the refrigerator may be overloaded or have an internal wiring deficiency. To prevent short-term variations, use a voltage regulator. (See Other Protective Devices for more information).


Transient impulses

A transient impulse is a sharp, sudden rise in voltage and can damage sensitive electronics. The power can jump up so fast to a few thousand volts over the normal 120 volts used in your home, you usually don't notice it. But to electronic appliances, it's like hitting a speed bump at 40 miles an hour. Don't let large loads share circuits with sensitive loads (e.g., computer, VCR, TV, stereo, fax). Most electric codes now require that large switching loads have their own circuit. In older homes, you may want to check with your electrician to make sure your system is safe and up to code. If you get a lot of disturbance from lightning, a transient voltage surge suppressor (TVSS) will protect your electronics from damage.



Poor reception or sound from your TV when someone in the house turns on a hair dryer, drill, vacuum cleaner or other appliance is noise interference. Loose wiring or poor grounding or manufacturing in your appliances can cause this. Poorly made appliances may not have enough shielding or filtering to prevent this interference.



For more information


Download our Power Quality in Your Home (PDF, 704 KB) brochure.

For questions or additional power quality information, please email us at: PowerQualityWeb@pge.com.