HP Superdome SX2000 Generic Site Preparation Guide, Fourth Edition - Page 8

Use uninterruptible power supplies (UPSs), backup generators, auto transfer devices, floor-mounted distribution transformers (less than 75-foot distances), and other alternatives for critical systems and applications demanding high availability. To ensure sufficient power quality, keep in mind: • The best voltage operating margin is in the middle of the distribution range. • High availability equipment should have UPS sourcing and dedicated breakers. • A few large UPSs provide more protection than numerous smaller cabinet UPSs. UPS Recommendations Use online versus offline UPSs for the highest availability environment. HP does not recommend the practice of sourcing a cabinet UPS from a room UPS as this can result in increased costs without providing more system availability. Indeed, this practice can introduce more system downtime than just a room-level or system-level UPS. UPSs that are compatible with present-day technology generally use pulse width modulation (PWM) and have ratings that are appropriate for a nonlinear load. Power Consumption Safety and regulatory labels on computer equipment list the ratings for maximum power consumption conditions. Even though you will not normally reach maximum conditions, size all electrical distribution infrastructures to meet maximum conditions. It is better to rate up rather than down. For example, if the marked electrical voltage is 15 amperes (A) on a server, depending on your local electrical code, the electrical infrastructure should include 20A receptacles, 20A sized wiring, and 20A breakers. Undersizing the wiring might save costs in the beginning, but it will cause problems as infrastructure grows. Average-sized wiring can be used with power quality devices, such as UPSs, but not with the electrical infrastructure. In determining the power requirements: • Size electrical infrastructure for maximum-rated consumption. • Size air-conditioning and UPSs with typical ratings, but realize that overloading might take place with additional growth of the infrastructure. NOTE: Set cooling for the maximum-rated power output of the room, and develop a growth plan for the cooling infrastructure. Grounding Systems WARNING! Follow electrical code when connecting equipment AC power ground wire to the AC distribution point. Failure to properly ground the equipment or the floor can lead to shock hazard. HP computer hardware has been tested only on systems where protective earth is integral to the electrical distribution system. This grounding is crucial for personnel safety and for maximum equipment availability and use. Observe the following precautions: • Neutral and ground wires have specific uses. Do not interchange them. • Do not use conduit grounds in place of a separate grounding conductor to each receptacle. • Size ground wires to be equal to the power source wires. • Do not daisy chain phase, neutral, and ground wires. • If the system is on raised flooring, use a 2-foot by 2-foot (61-cm by 61-cm) grounding grid. 8 General Site Preparation Guidelines