Power disturbances can have their source in either the utility or customer wiring system and/or equipment. These disturbances can be classified into categories that can vary in effect, duration and intensity. The chart below lists the most common categories of disturbances, their causes and some potential solutions.
Power Outages | Transient (Surge) | Sag or Swell | Noise | Harmonic Distortion | Undervoltage | Overvoltage
| Disturbance Type | Description | Possible Causes | Symptoms/Effects | Potential Solutions |
| Power Outage |
Total interruption of electrical supply: Momentary outages last from one-half second to 3 seconds Temporary outages last from 3 seconds to 1 minute Long-term outages last longer than 1 minute |
Accidents, acts of nature, etc. which require the proper operation of utility equipment (fuses, reclosers, etc.) Internal short circuits requiring the proper operation of a customer's breakers and fuses |
System shutdown Loss of computer/ controller memory Hardware damage Product loss or damage |
Uninterruptible Power Supply (UPS)
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| Disturbance Type | Description | Possible Causes | Symptoms/Effects | Potential Solutions |
| Transient (Surge) |
A subcycle disturbance in the AC waveform, resulting in a sharp but brief increase in voltage | Surges are caused by storms (lightning), operation of utility fuses, reclosers and breakers Internal causes are turning on or off large equipment and capacitor switching |
Computer lock-up, processing errors and data loss Burned circuit boards, electrical insulation damage and equipment damage |
Uninterruptible Power Supplies with built in surge suppression |
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| Disturbance Type | Description | Possible Causes | Symptoms/Effects | Potential Solutions |
Sag / |
Any short-term (one-half cycle to 3 seconds) decrease (sag) or increase (swell) in voltage Sags account for up to 87% of all power disturbances (according to a Bell Labs study) |
Major equipment shut-down and/or restart Short circuits Utility equipment failure or utility switching |
Memory loss and data errors Equipment shutdown Flickering lights Motors stalling or stopping and decreased motor life |
Voltage regulators |
| Disturbance Type | Description | Possible Causes | Symptoms/Effects | Potential Solutions |
| Noise | An unwanted high-frequency electrical signal that alters the normal voltage pattern (sine wave) | Interference from radio or TV transmission Operation of electronic equipment |
Lock-up of sensitive equipment Data loss and processing errors Distorted audio and video reception |
Power line filters |
| Disturbance Type | Description | Possible Causes | Symptoms/Effects | Potential Solutions |
| Harmonic Distortion | The alteration of the normal voltage pattern (sine wave) due to equipment generating frequencies other than the standard 60 cycles per second | Electronic ballasts and other non-linear loads like switch-mode power supplies and variable frequency drives | Overheating of electrical equipment and wiring Decreased motor performance Improper operation of breakers, relays or fuses |
Harmonic filters Improved wiring and grounding Isolated loads Line reactors |
| Disturbance Type | Description | Possible Causes | Symptoms/Effects | Potential Solutions |
| Undervoltage/ Overvoltage | Any long-term change lasting more than a minute, below or above normal voltage | Overloaded wiring or equipment Large load swings or improper transformer settings Undersized wiring and faulty or poor electrical connections |
Dim or bright lights Equipment shutdown Overheating of motors or lights Reduced efficiency or life of electrical equipment |
Verify electrical connections and wiring Relocate equipment Reduced voltage motor starters and voltage ride-through equipment |
