Voltage and frequency limits

Voltage and frequency limits must be maintained to ensure proper functioning of your system.

The phase-to-phase steady-state voltage must be maintained within plus six percent to minus 10 percent of the normal rated voltage, which is measured at the receptacle when the system is operating. A voltage surge or sag condition must not exceed plus 15 percent or minus 18 percent of the nominal voltage and must return to within a steady-state tolerance of plus 6 percent or minus 10 percent of normal rated voltage within 0.5 second.

Some systems might require special considerations and might have more or less restrictive specifications. See the individual system specifications for actual requirements. Because of the possibility of brownouts (planned voltage reduction by the utility company) or other marginal voltage conditions, installing a voltage monitor might be advisable.

The phase frequency must be maintained at 50 or 60 Hz + 0.5 Hz.

The value of any of the three phase-to-phase equipment voltages in the three-phase system must not differ by more than 2.5 percent from the arithmetic average of the three voltages. All three line-to-line voltages must be within the limits previously specified.

The maximum total harmonic content of the power system voltage waveforms on the equipment feeder must not exceed 5 percent with the equipment operating.