HP EML E-series Tape Libraries - Manual (Page 125)

D Installing a redundant PDU
PDU components
The library comes with one PDU installed. For a variety of reasons, it may be desirable or necessary
to add a second PDU to the library 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
power strips 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 library may each contribute a maximum of 0.5 mA. This means
no more than seven of the library power supplies may be attached to a single PDU. A fully configured
library, 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 library 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 library 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 library 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 library rack is to add another layer of power
redundancy to the product. As redundant power supplies are added to library 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 library 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 library 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.
Power rating
As was the case with leakage current, if equipment is added to the library rack from other sources, it is
your responsibility to make sure the power rating of the PDU and power cords are not exceeded by the
load of this additional equipment. The power rating of the PDU is sufficient to power up to seven power
Enterprise Modular Library E-Series 125