Site Preparation Guide, Eighth Edition - Superdome HP 9000 Systems

Chapter 2
Electrical and Environmental Guidelines
Electrical Factors
41
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.
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.
Raceway Systems (Electrical Conduits)
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
• Liquidtight with RFI strain relief (most commonly used with raised floors)
• Plenum-grade cables
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.
The IOX and Superdome are safety grounded through the green (ground) wire in each AC power cord. In the
IOX, this ground passes through the AC power cord entry into the XPC and connects internally to the XPC
chassis. The XUC chassis and each ICE chassis are grounded through their respective DC power cords from
the XPC. Additional safety grounding must be provided for networking equipment.
Power Routing
Power drops and interface cables from the equipment are routed down from the power panel, through a
grommet-protected opening (beneath the floor level), and under the floor panels.
Grounding Systems
Superdome servers require two methods of grounding:
• Power distribution safety grounding
• High frequency intercabinet grounding
Power Distribution Safety Grounding
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 may 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 equipotential ground to all points.