Fujitsu PRIMERGY BX900 S1 Operating Manual page 54

Installing the hardware
With 4 power supply units, you must connect units 2 and 3 to the first
source (phase) and units 5 and 6 to the second. Thus 2+2 redundancy is
supported; the system continues to run if one source fails, provided the
remaining 2 power supplies are sufficient to deliver the required power.
Power system with 3 AC sources (phases) available
With 6 power supply units, you must connect units 1 and 4 to the first AC
source (phase), units 2 and 5 to the second, and units 3 and 6 to the third.
Thus 4+2 redundancy is supported; the system continues to run if one
source fails, provided the remaining 4 power supplies are sufficient to
deliver the required power.
With 3 power supply units, you must connect each one to a different
source. Thus 2+1 redundancy is supported; the system continues to run
if one source fails, provided the remaining 2 power supply units are
sufficient to deliver the required power.
54 Operating Manual
BX900 S1