The BPA option is required for clients who order an Internal Battery Feature (IBF), Water  Cooling Unit (WCU), or Balanced Power. The BPA requires two or four power cords. All BPAs  are concurrently repairable in the field. The 8561 operates from 2 or 4 fully redundant power supplies. These redundant power  supplies each have their own power cords, or pair of power cords, which allows the system to  survive the loss of customer power to either power cord or power cord pair.  If power is interrupted to one of the power supplies, the other power supply assumes the  entire load and the system continues to operate without interruption. Therefore, the power  cords for each power supply must be wired to support the entire power load of the system.  For the most reliable availability, the power cords in the rear of the frame should be powered  from different PDUs. All power cords exit through the rear of the frame. The utility current  distribution across the phase conductors (phase current balance) depends on the system  configuration. Each front end power supply is provided with phase switching redundancy.  The loss of an input phase is detected and the total input current is switched to the remaining  phase pair without any power interruption. Depending on the configuration input power draw,  the system can run from several minutes to indefinitely in this condition. Because most single  phase losses are transients that recover in seconds, this redundancy provides protection  against virtually all single phase outages. Power cords for the BPAs are attached to the options that are listed in Table 11-5. The source power cords ratings for BPA systems are listed in Table 11-6. Table 11-5 Power cords for the BPAs Table 11-6 Source power cords for BPA a. Japan (same physical cord as Note b) b. US, Canada (same physical cord as Note a) c. US, Canada only d. US only Chapter 11. Environmentals  455 Supply type Nominal voltage range Voltage tolerance Frequency range Two or four redundant  3-phase power cords 200 - 480 V AC 180 - 508 V AC 50 / 60 Hz Source type Frequency Input voltage range Rated input current Three-phase (60A plug)  50 / 60 Hz 200 V a 50 A Three-phase (60A plug) 50 / 60 Hz 208 - 240 V b 48 A Three-phase (30A plug) 50 / 60 Hz 380 V - 415 V c 24 A Three-phase (30A plug) 60 Hz 480 V d 20 A Three-phase (63A no plug) 50 / 60 Hz 220  V - 480 V 48 A Three-phase (32A no plug) 50 / 60 Hz 380 V - 415  V 25 A Power requirements