Dirty Power. A normal sine wave (120VAC) represents normal clean power. The abnormal (green) wave represents noise, power surges, electrical spikes, drop-outs, or brownouts(drop in voltage) commonly named "dirty power".


Dirty power (Noise) is any electrical current or specific voltage that varies. Dirty power from a medical device perspective is power that is:

  • Always as the exact voltage (120 VAC in the US)
  • Does not vary by more than 10% with a Load versus a No Load condition
  • For AC waveforms, always at the specific Hertz (60 Hz in the US; 50 Hz overseas)
  • The AC waveform looks 100% consistent like a sine wave. If any deviations or irregularities spotted on the waveform may result in slightly erratic behavior in electronic components causing dirty (unregulated) power.[1][2] This distortion (Noise) of the pure sine wave, or alternating current, from a utility company may be caused by line switching, radio transmitters, manufacturing equipment, and/or line voltage fluctuations from various sources. Dirty power can cause errors in computer files and programs.[3]

Surge Protection[]

Noise-filtration filters or surge protection devices can reduce electromagnetic and radio frequency interference (EMI and RFI). These devices along with built in fuse protection will save your equipment even if the suppressor is destroyed.


On September 29, 2009, UL 1449 Third Edition,re-defined performance testing and nomenclature, which effectively reboots the surge industry. UL 1449’s per-performance testing provides a way to compare newly evaluated Surge Protective Devices, formerly known as Transient Voltage Surge Suppressors.[4]


  1. Superuser. What is dirty power? accessdate 7/29/11. [1]
  2. John R. Quain. Protect Your PC From Dirty Power. June 30, 1997. [2]
  3. Quentin Wagenfield. Protect Your Equipment from Dirty Power: How to deal with sags, surges, spikes, and other power problem. 3/01/2000. [3].
  4. UL StandardsInfoNet . Surge Protective Devices: UL 1449. [4]


See also[]