“The Dirty Half Dozen” A list of the most commonly encountered power disturbances “Dirty Half Dozen” Symptoms Probable Causes Typical Solutions Computers Fault Clearing Power Conditioner ∗ System lock-up (either side of the meter) ∗ Constant Voltage Transformers Voltage Sags ∗ System crash ∗ Weather (CVT) ∗ Data loss and errors ∗ Fires ∗ Motor Generator Process Control ∗ Trees Uninterruptible Power Supply (UPS) ∗ Loss of control ∗ Animals ∗ On-line ∗ System shutdown ∗ People ∗ Line-interactive Motors ∗ Equipment ∗ Off-line ∗ Overheating Large motor start-up Stagger motor starts ∗ Contact damage Undersized distribution system Size infrastructure properly Nuisance tripping ASDs Lighting ∗ Lower output ∗ HID extinguish Computers Lightning strikes Transient Voltage Surge Suppression ∗ System lock-up Capacitor switching (TVSS) Transient Arcing faults ∗ Data loss and error ∗ Power Conditioner with TVSS Load switching ∗ Component damage ∗ Uninterruptible Power Supply Overvoltages Process Control (UPS) with (TVSS) Inductors ∗ Loss of control Motors ∗ Insulation damage ∗ Nuisance tripping ASDs All electrical equipment shuts Equipment failure Uninterruptible Power Supply (UPS) down Loose or broken power line ∗ On-line Interruptions fittings ∗ Line-interactive Safety device tripping ∗ Off-line Back-up generators Overheated distribution Non-linear loads Oversized and dedicated neutrals neutrals and transformers Single phase computers “K” rated transformers Harmonics Voltage distortion can cause Electronic power supplies Filters timing errors ASDs Nuisance tripping GFRs Data errors Motors/welders Separate loads Monitor noise or wavy screen Improper grounding Isolation transformer EMI/RFI/EMF Process control errors Electronic devices Proper grounding-shielding Some power conditioners “electrical noise” Some UPSs, some TVSSs Computers Piecemeal work Perform wire and grounding survey ∗ System lock-up Rapid expansion Keep single-line diagram up to date Wiring and Out of date electrical drawings Follow IEEE guidelines ∗ Data loss and errors Lack of maintenance Specify lower harmonic equipment ∗ Component damage Grounding Aluminum wiring Perform regular maintenance Safety devices Problems Large percentage of harmonic Review entire system ∗ Nuisance tripping GFRs loads ∗ Circuit breaker tripping Manufacturers’ grounding ∗ Failure to operate due to specifications poor grounding Misoperation of equipment Courtesy of Dranetz-BMI