Urgent Alert

Power Quality

Power-quality problems

Power quality

Many problems can result from poor power quality, especially in today's complex microelectronics environment. In the past, electrical disturbances on mechanical equipment went unnoticed. Now, however, electrical disturbances can upset today's high-tech equipment operations severely.


Approximately 80 percent of power quality problems originate from the customer's side of the meter. It's important for facility owners, managers, designers and other high-tech equipment users to understand and learn how to avoid power disturbances. Review the following for a general overview of power quality:


Residential and small commercial: Power Quality in Your Home (PDF)


Commercial/industrial: Understanding and Avoiding Commercial Power Disturbances (PDF)

Power quality and voltage stability


It's normal for your electric service voltage to vary within the prescribed limits. These fluctuations can result from the normal operation of a utility's electric transmission and distribution system, among other reasons. Voltage changes will not usually cause problems for your equipment or facilities. Certain electronic equipment may be sensitive to these fluctuations, however, which may cause problems.


You are responsible for obtaining any devices needed to protect your sensitive equipment that can't operate within the voltage variations of our normal electric service. Electric Rule 2, on file with the California Public Utilities Commission, specifies these variations. PG&E is not liable for damage to your equipment or any other damage from variations in service voltage allowable under this rule.

Review electric rule 2 (PDF)

Power-quality problems


Power-quality problems arise when system incompatibility occurs between the AC power and the equipment. Either the quality of the AC distribution system or the AC voltage can contribute to power quality problems. In order to find the right solution or solutions, it’s important to diagnose the problems correctly. Some typical power quality problems are:


  • Processing errors
  • Soft failures such as computer reset or lockout
  • Hard failure of electronic components
  • Nuisance tripping in process control equipment

Analyze power-quality problems


When analyzing a potential power-quality problem, it’s important to keep a trouble log. This helps to connect the problem to other events such as equipment operations or even utility problems. Check out PG&E's “Checklist to Solve Power Problems for Sensitive Equipment” to help identify and mitigate power problems for sensitive equipment.


The checklist includes questions you should answer in your trouble log to help identify possible causes and solutions. Once you've diagnosed the problem (e.g., voltage sags, outages, impulses, harmonics, electrical noise, voltage and current imbalances, interference or wiring and grounding, etc.) correctly, you can take preventive measures to mitigate the problem. Sometimes the solution can be as simple as adjusting your equipment to make it less sensitive to power variations. Be sure to adjust in a manner that does not void any warranties.


Download the checklist to solve power problems for sensitive equipment (PDF)


Power Notes


Our PG&E Power Notes on the following topics may help you identify and solve your power-quality problems or concerns.

Power Quality Bulletins


PG&E's Power Quality Bulletins may also help you identify and solve your power-quality problems or concerns.

A black box is a device or system with external wires that supposedly can do something something beneficial. In many cases, what's inside the box is a mystery. Many devices and systems on the market claim to improve the power quality or reliability of electric service. Some devices also claim to save energy. Often the technological claims are not clear or have not been verified in accordance with industry standards. Learn more in our Bulletin on the subject.


Download power quality bulletin - Issue NO. 1 (PDF)

Have you ever been shocked when you touched a metal fixture near a swimming pool or when you touched the showerhead fixture in your home? And for dairy farmers, have you noticed a reduction in milk production? These may all be symptoms of stray voltage. Learn more in our Bulletin on the subject.


Download power quality bulletin - Issue NO. 2 (PDF)

Interruptions in manufacturing processes can be very costly. They can cause potentially millions of dollars in lost revenue per day. Such interruptions can be due to voltage sag events, which are the most important power-quality problem facing many industrial customers, especially those with a process. Learn more in our Bulletin on the subject.


Download power quality bulletin - Issue NO. 3 (PDF)

Additional resources

For more information

If you have questions or need additional power quality information, email us at PowerQualityWeb@pge.com.