Power Considerations; Power Redundancy; Non-Redundant; High Line Voltage Versus Low Line Voltage - HP 245161-B22 - 10642 42U Rack Shock Pallet Best Practices Manual

Power considerations

Power is best managed within the rack by the use of a power distribution unit (PDU). Depending on
the configuration, it may be necessary or desirable to use multiple PDUs to connect all devices inside
the rack.
Each PDU should be connected to a dedicated (unshared) branch circuit that is suitably rated for the
continuous load of all the equipment connected to it. The total power load for a PDU should not
exceed 80 percent of the branch circuit rating.
If a PDU is not used, each piece of equipment within the rack should be connected to a dedicated
branch circuit.

Power redundancy

High-availability Information Technology equipment such as servers and storage devices can be
configured with backup or redundant power sources and power supplies in either of the following
configurations:
• 1+1 design: Two power supplies can be provided where either power supply is capable of
sustaining the associated equipment's power demand.
• N+1 design: Typically three power supplies are provided, requiring at least two to handle the
equipment's power demand. If one fails, the other two remain on line with enough capacity to meet
the power demand.
It is important that the wiring and branch circuitry to each installation be suitably rated for the power
demand of the connected equipment. Routing the power through separate branch circuits, breaker
panels and PDUs is also recommended to provide additional redundancy.

Non-redundant

For equipment provided with a single source of power, all components should be connected to the
same power distribution device (PDU or UPS). The power distribution device should be suitably rated
for the connected load. If the total load exceeds the rating of the power distribution device, obtain a
suitably rated device or add a second power distribution device and divide the load equally between
the devices.

High line voltage versus low line voltage

HP recommends that rack-optimized equipment is installed for operating at high line voltage (200-
240V AC).
All HP products that are optimized for rack mounting have wide-range power supply inputs designed
to operate at a voltage range of 100--240V.
Benefits that support high line voltage operation of an installation are as follows:
• Power supplies run more efficiently and waste less power when operating at 200--240V, thus
saving electrical power.
• Greater power capacity in a single rack. For the same size circuit, almost twice the power can be
delivered to a rack at high line versus low line. For example, an 115V 30A branch circuit can
deliver 3450VA to a rack, while a 230V 30A branch can deliver 6900 VA to a rack.
• Some products require 200-240V input power to operate at their full-rated capacity.
• Power supplies run cooler at higher input voltages and therefore will last longer and improve
overall availability. Also, because they run cooler, they produce less waste heat contributing to
lower cooling costs.
• Keeping input currents lower allows the use of smaller, more standardized power connections.
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