Chapter 2
General System and Facility Guidelines
Electrical Factors
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Sources of Voltage Fluctuations
Voltage fluctuations, sometimes called glitches, affect the quality of electrical power. Common sources of these
fluctuations 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
Precautions have 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 HP 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.
Distribution Hardware
This section describes wire selection and the types of raceways (electrical conduits) used in the distribution
system.
Wire Selection
Use copper conductors instead of aluminum, as aluminum’s coefficient of expansion differs significantly from
that of other metals used in power hardware. Because of this difference, aluminum conductors can cause
connector hardware to work loose, overheat, and fail.
