Power Quality

Many problems can result from poor power quality, especially in today's complex microelectronics environment. Electrical disturbances on mechanical equipment went unnoticeable in the past but can upset today’s high-tech equipment operations severely. Because approximately 80 percent of all power-quality problems originate from the customer's side of the meter, facility owners, managers, designers and other high-tech equipment users need to understand and avoid power disturbances. For a general overview of power quality for residential and small commercial premises, visit Power Quality in Your Home (PDF, 575 KB). For commercial/industrial customers, visit Understanding and Avoiding Commercial Power Disturbances (PDF, 1 MB).

Power Quality and Voltage Stability

It is 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. Usually, these voltage changes will not cause problems for your equipment or facilities. However, certain electronic equipment may be sensitive to these voltage fluctuations, causing problems.

You are responsible to provide any devices needed to protect your sensitive equipment that can't operate within the voltage variations of our normal electric service. Our Electric Rule 2 (PDF) (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.

Power Quality-Related 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 each case, the solution is different. So, in order to find the right solution or solutions, it is 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 is 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 Power Note on A Self Checklist to Solve Power Problems for Sensitive Equipment (PDF, 30 KB). In the checklist are questions you should answer in your trouble log to help identify possible causes and possible solutions. Once you have diagnosed the problem correctly (such as voltage sags, outages, impulses, harmonics, electrical noise, voltage and current imbalances, interference or wiring and grounding, etc.), 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.

Fee-based Power Quality Consulting Services

If you have a power quality question or problem you would like to discuss with us, please e-mail us at PowerQualityWeb@pge.com. We will try to help you resolve your power quality problem. However, if you cannot resolve it yourself, for a fee, we will attempt to identify the cause of your power-quality problem and recommend power-quality mitigation measures. For more information, check out PG&E's Power Quality Consulting Services for a Fee (PDF, 27 KB).

Power Notes

These power notes on specific subjects may help you identify and solve your particular power-quality problems and concerns.

More Power Quality Information

Other Resources
Here is reference material to help you:

  • Find out what power-quality standards or guidelines are available
  • Better understand power-quality issues
  • Protect their sensitive equipment.
  • See which manufacturers, vendors and consultants are working on power quality

Other Web Sites
Utilize other online resources (such as trade magazines, technical organizations, nonprofit groups and manufacturers) to help you in analyze and solve your power-quality problems.

Power Quality Bulletins

Black Box (PDF, 27 KB)
A black box is a device or system with external wires which claims it can do something. 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.

Stray Voltage (2_STRAY_VOLT.PDF, 19 KB)
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.

SEMI Standards F47/F42 (3-VOLT_SAGIMM_STD-8-10-07.PDF, 49 KB)
As you may already be aware, interruptions in manufacturing processes can be very costly, causing 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.


For general questions or additional information regarding power quality, please email us at: PowerQualityWeb@pge.com. For specific concerns regarding your electrical service, please contact PG&E Customer Service at 1-800-743-5000.