D Installing A Redundant Pdu; Leakage Current; Redundancy - HP E Series User Manual

D Installing a redundant PDU

This appendix provides suggestions as to when an additional, redundant power distribution unit (PDU)
should be installed in the HP StorageWorks Enterprise Modular Library (EML) E-Series.
The EML product comes with one PDU installed. For a variety of reasons, it may be desirable or
necessary to add a second PDU to the EML rack. The factors that determine when to add a second PDU
are described below.
The main PDU components are:
• High voltage modular PDU, 200–240 VAC, 16 amp, part number 252663-B24 (kit includes two
extension bars and mounting hardware)
• Main power cord, L6-20P 20 amp, 220 V, twist lock, part number 340653-001
• Power cords (PDU to library), 1/2 meter, part number 142257-B28

Leakage current

The most overriding reason to add a second PDU to the rack is to meet safety requirements for leakage
current. Regulations limit the amount of leakage current per power outlet to 3.5 mA. This is the amount of
current that may be returned through the ground line to the wall outlet, and therefore is the amount of
leakage current allowed per PDU.
The individual power supplies of the EML may each contribute a maximum of 0.5 mA. This means no
more than seven of the EML power supplies may be attached to a single PDU. A fully configured EML,
with redundant power supplies, would necessitate 10 power supplies. In that configuration, a second
PDU is certainly required. Even a 32U-high configuration of the EML with redundant power supplies would
require a second PDU. Even if redundant power supplies are not currently installed, you should consider
adding a second PDU when the EML is expanded above 24U in height. With a second PDU installed,
upgrading to redundant power supplies in the future is simplified by being able to just slide them into
place and connect them to the power strip.
If equipment is added to the EML rack from other sources, it is your responsibility to determine the
maximum leakage current from all the equipment using the PDU so that the 3.5 mA limit on a single PDU
is not exceeded.

Redundancy

Another important reason to add a second PDU to the EML rack is to add another layer of power
redundancy to the product. As redundant power supplies are added to EML modules, the system can be
made even more failsafe by powering individual power supplies, one from each module, with separate
AC power circuits. This requires a second PDU.
Every EML module level (for example, the base module, card cage expansion module, tape drive
expansion module, and so on) can have redundant power supplies added as an option. Each module
level, with each power supply powered from different AC circuits, ensures continued EML operation
should one of the AC power outlets fail. The location of the power strips for the second PDU are installed
in a manner such that the power cords of the redundant power supplies of each module level can easily
reach the PDU.
Enterprise Modular Library E-Series user guide 125