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Sustained Interruption
A planned or accidental total loss of power that lasts more than two minutes.

  • Possible Causes: Equipment failure, weather, animals on power lines, auto accidents, mylar balloons, etc.
  • Effect: The electrical system shuts down in the affected area.

Temporary Interruption
A planned or accidental total loss of power that lasts between two seconds and two minutes.

  • Possible Causes: Equipment failure, weather, animals on power lines, auto accidents, mylar balloons, etc.
  • Effect: The electrical system temporarily shuts down in the affected area.

Momentary Interruption
A planned or accidental loss of power that lasts up to two seconds.

  • Possible Causes: Utility switching operations.
  • Effects: Equipment trips off, programming is lost, disk drives crash, etc.

Sag or Undervoltage
A sag is a decrease in voltage below the prescribed input voltage range that lasts up to three seconds. An undervoltage is a sag that lasts between three seconds and two minutes.

  • Start-up or shut-down of major equipment, short circuits or fault clearing, overloading the distribution system or customer wiring.
  • Effects: Data errors, dim lights, equipment shutdown or reset, errors in sensitive equipment, low efficiency, reduced life of equipment.

Swell or Overvoltage
A swell is an increase in voltage above the prescribed input voltage range that lasts up to three seconds. Overvoltages are swells that last between three seconds and two minutes.

  • Possible Causes: Incorrect transformer tap settings, improper application of power factor correction capacitors.
  • Effects: Overheating and reduced life of electrical equipment such as motors, heaters, etc.

Transient or Spike
A sudden change in voltage up to several hundred or thousand volts that lasts from a fraction of a microsecond to several milliseconds.

  • Possible Causes: Lightning, static discharges, utility switching operations, starting or stopping major equipment or machinery.
  • Effects: Burned circuit boards, processing errors, or data errors.

Notch
A disturbance of opposite polarity from the waveform that lasts milliseconds.

  • Possible Causes: Lightning, static discharges, utility switching operations, starting or stopping major equipment or machinery.
  • Effects: Burned circuit boards, processing errors, or data errors.

Noise
A sporadic, unwanted electrical signal of high frequency from other equipment.

  • Possible Causes: Electromagnetic interference from appliances, microwave and radar transmissions, radio/TV broadcasts, laser printers, heaters, thermostats, loose wiring, improper grounding, etc.
  • Effects: Processing errors or data loss.

Harmonic Distortion
Voltages or currents at frequencies that are integer multiples of 60Hz frequencies (i.e. 120Hz, 180Hz, 240Hz, etc.)

  • Possible Causes: Non-linear loads.
  • Effects: Overheating of motors, transformers, and wiring.

 

Last updated: 10/12/2011 9:53:11 AM