Systems that specify two power cords can be brought up with one power cord and continue to  run. The larger systems that have a minimum of four BPR pairs that are installed must have four  power cords installed. Systems that specify four power cords can be started with two power  cords on the  same side  with sufficient power to keep the system running. Power cords attach to a three-phase, 50/60 Hz, 200 - 480 V AC power source, or a 380 - 520  V DC power source.  A Balanced Power Plan Ahead feature is available for future growth, which helps to ensure  adequate and balanced power for all possible configurations. With this feature, system  downtime for upgrading a server is eliminated by including the maximum power requirements  in terms of BPRs and power cords to your installation.  For ancillary equipment, such as the Hardware Management Console, its display, and its  switch, more single phase outlets are required. The power requirements depend on the cooling facility that is installed, and on the number of  CPC drawers and I/O units that are installed. For more information about the requirements  that are related to the number of installed I/O units, see 10.1.2, “Power requirements and  consumption” on page 391. The High Voltage Direct Current power feature is an option for z14 servers. It allows z14  servers to directly use the high voltage (HV) DC distribution, as shown in Figure 2-26. A direct  HV DC data center power design can improve data center energy efficiency by removing the  need for a DC-to-AC inversion step. The z14 bulk power supplies were modified to support HV DC, so the only difference in the  shipped hardware to implement this option is the DC power cords. Because HV DC is a new  technology, multiple proposed standards are available.  2.8.2 High Voltage Direct Current power feature 78  IBM z14 (3906) Technical Guide Figure 2-26 AC versus DC distribution High Voltage AC Power  Step down substation Transfer Switch 480 VAC 3 phase UPS Batteries AC/DC DC/AC 480 VAC Step down PDU 208 VAC 3 phase AC/DC DC/DC 410V DC 12V DC Transfer Switch Transfer Switch High Voltage DC Power  Step down substation 480 VAC 3 phase DC Input UPS AC/DC Batteries DC/DC Batteries 520 VDC 520 VDC AC/DC DC/DC DC/DC AC/DC 12V DC 12V DC UPS PSU PSU Server Server Server PSU Losses ~13% Losses ~4%