Distribution Hardware; Wire Selection; Raceways; Building Distribution - HP Cluster Platform Introduction v2010 Introduction Manual

• Screening to cancel out the effects of undesirable transmissions
• Lightning arresters on power cables to protect equipment against electrical storms
The following guidelines provide the best possible performance of power distribution systems:
• Dedicated power source that isolates the cluster's power distribution system from other
circuits in the facility.
• Missing-phase and low-voltage detectors that shut down automatically when a severe power
disruption occurs.
• Online uninterruptable power supply (UPS) that keep the input voltage to devices constant
and should be considered if outages of one-half cycle or more are common. Refer to qualified
contractors or HP consultants for each situation.
C.1.3 Distribution Hardware
This section describes wire selection and the types of raceways (electrical conduits) used in the
distribution system. Wire size is dictated by circuit breaker sizing and local safety codes.
C.1.3.1 Wire Selection
Use copper conductors instead of aluminum, because 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 loosen, overheat, and fail.
C.1.3.2 Raceways
Raceways (electrical conduits) form part of the protective ground path for personnel and
equipment. Raceways protect the wiring from accidental damage and also provide a heat sink
for the wires. Any of the following types may be used:
• Electrical metallic tubing (EMT) thin-wall tubing
• Rigid (metal) conduit
• Water-resistant cladding, with RFI strain relief (most commonly used with raised floors)
• Plenum-grade cables
C.1.3.3 Building Distribution
All building feeders and branch circuitry should be in rigid metallic conduit with proper
connectors (to provide ground continuity). Conduit that is exposed and subject to damage should
be constructed of rigid galvanized steel. Cluster components are safety grounded through the
green (ground) wire in each AC power cord. Power drops from the cluster's PDUs are routed
from the bottom of each rack, because the PDUs are always located in the lowest rack positions.
The power distribution safety grounding system consists of connecting various points in the
power distribution system to earth ground using green (green/yellow) wire ground conductors.
Having these ground connections tied to metal chassis parts that might be touched protects
computer room personnel against shock hazard from current leakage and fault conditions. Power
distribution systems consist of several parts. Hewlett-Packard recommends that these parts be
solidly interconnected to provide an potential ground to all points:
• Main building electrical ground – The main electrical service entrance equipment should
have an earth ground connection, as required by applicable codes. Connections such as a
grounding rod, building steel, or a conductive-type cold water service pipe provide an earth
ground.
• Electrical conduit ground – To provide a continuous grounding system, all electrical conduits
should be made of rigid metallic conduit that is securely connected together or bonded to
panels and electrical boxes.
• Power panel ground – Each power panel should be grounded to the electrical service entrance
with green or green and yellow wire ground conductors. These ground conductors should
be sized according to applicable codes in force (based on circuit over current device ratings).
52 General Guidelines for the Computer Room