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Appendix C
Site Preparation
Power Quality
104
Power Quality
This equipment is designed to operate over a wide range of voltages and frequencies. It has been tested and
shown to comply with EMC Specification EN50082. However, damage can occur if these ranges are exceeded.
Severe electrical disturbances can exceed the design specifications of the equipment.
Sources of Electrical Disturbances
Electrical disturbances, sometimes called glitches, affect the quality of electrical power. Common sources of
these disturbances are:
• Fluctuations occurring within the facility’s distribution system
• Utility service low-voltage conditions (such as sags or brownouts)
• Wide and rapid variations in input voltage levels
• Wide and rapid variations in input power frequency
• Electrical storms
• Large inductive sources (such as motors and welders)
• Faults in the distribution system wiring (such as loose connections)
• Microwave, radar, radio, or cell phone transmissions
Power System Protection
Computer systems can be protected from the sources of many of these electrical disturbances by using:
• A dedicated power distribution system
• Power conditioning equipment
• Over- and under-voltage detection and protection circuits
• Screening to cancel out the effects of undesirable transmissions
• Lightning arresters on power cables to protect equipment against electrical storms
Every precaution has been taken during power distribution system design to provide immunity to power
outages of less than one cycle. However, testing cannot conclusively rule out loss of service. Therefore,
adherence to the following guidelines provides the best possible performance of power distribution systems
for server equipment:
• Dedicated power source—Isolates server power distribution system from other circuits in the facility.
• Missing-phase and low-voltage detectors—Shuts equipment down automatically when a severe power
disruption occurs. For peripheral equipment, these devices are recommended but optional.
• Online uninterruptible power supply (UPS)—Keeps input voltage to devices constant and should be
considered if outages of one-half cycle or more are common. Refer to qualified contractors or consultants
for each situation.