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Troubleshooting tips for power quality problems

Common Problems Symptoms Items to look for


Lighting dimming, computer lockups, relay and contactor chatter or complete dropout, equipment and system shutdowns. Spurious and unexplained alarms and shutdowns.

Starting large loads, especially large inductive loads such as motors. Similar operations in neighboring facilities. Severe weather.


Failed power supply sections in equipment. Overvoltage shutdowns and alarms on variable frequency drives (VFDs).

Fault on single phase of three-phase system. Sudden load decrease. Capacitor bank switching.


Flashover and arcing effects in distribution equipment. Damaged insulation. Failed electronics. Computer lockups.

Lightning strikes. Switching of capacitors. Reenergizing systems after a power failure. Sudden stoppage of large equipment. Dirty or worn contactors.


Equipment shutdowns.

Momentary loss of utility power.


Overheated three-phase motors and transformers.

Unbalanced loads across individual phases of three-phase panelboards. Unbalanced utility supply. Operation of single-phase welders. Open-delta transformers.


Overheated neutral conductors. Overheated transformers. Overheated inductive motors. Spurious and unexplained alarms and shutdowns of electronic equipment

Nonlinear loads such as switching power supplies. Converter sections of uninterruptible power supply (UPS), VFDs, and battery chargers. Welders. Arc furnaces.

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