Periodical Instantaneous Voltage Drop (HIOKI)


Monitoring location: Retail store, 1-phase 2-wire, 100V outlet

Duration: 2 weeks


When analyzing the voltage RMS value fluctuation, the following two phenomena were observed. (The graph shows measurement during 12 hours in the night for a period of 2 weeks.)

  1. Maximum value: 106.70Vrms, Average value: 102.53Vrms, Minimum value 93.25Vrms
  2. Instantaneous voltage drop occurred at about every 13 minutes.
Voltage Fluctuation

Voltage Fluctuation

The cause of the instantaneous voltage drop every 13 minutes is assumed to have originated from an electronic device connected to the line as this outlet is turned on or works periodically via a timer.

The device may have a high inrush current – common in equipment such as laser printers, copy machines, electric heaters, etc. A laser printer consumes current periodically, and causes a voltage drop as a result of its start-up current consumption. An electric heater also causes a voltage drop from the periodic inrush current coming from the power cycling of the thermostat.


There are many instantaneous voltage drops, but the minimum voltage is 93.25Vrms which is about 7% lower than the nominal voltage. Most equipment works normally at this voltage level. However, the customer should be careful when adding a new load.

Source : Guidebook for Power Quality Measurement, HIOKI E.E. Corporation