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VR101S
Users Manual
42
Sag An operating voltage of 90% of nominal volts or
less
Swell More than one cycle above 10% of nominal
Dropout Power loss of 1 ms to 1 s
Outage More than 1 s of power loss
Positive Transient A momentary overvoltage of 4 ms
or less
Negative Transient A momentary undervoltage of 4
ms or less
Frequency Variation ± 1Hz of the fundamental
frequency (50 or 60Hz)
How Bad is Bad?
Manufacturers of electrical equipment may specify
requirements for power quality. The tolerances below
are general and do not apply to all manufacturers of
sensitive electronic equipment. Generally, sensitive
equipment (computers) can operate within the following
voltage tolerances:
Swells
• Up to 10% above nominal continuously
• Up to 30% above nominal for less than 0.5 seconds
Sags
• Down to 10% below nominal continuously
• Down to 30% below nominal for less than 0.5
seconds
• Down to 0 volts for 4 ms (acceptable but not
recommended)
Transients
• Not to exceed ± 150% of sine voltage for more than
0.2 ms
Frequency Variation
• ± 1Hz
The CBEMA Curve
The Computer Business Equipment Manufacturers
Association (CBEMA) has published a susceptibility
graph detailing how various types of power line
disturbances affect sensitive electronic equipment (see
below).