Fujitsu Siemens Computers PRIMERGY BX600 S2 Operating Manual page 47

Installing the Hardware
I
Please make sure that each of the power supply units is connected to a
different phase. This will provide you with additional phase redundancy
for high availability configurations. If one phase has failed, the power
supply units connected to the other phases keep active. You can get full
phase redundancy with up to three power supply units. With four power
supply units, two of them are to be connected to one phase (see also
"Related Publications" on page
Phase redundancy is possible in regions, where a single phase provides
200 - 240V; in other regions with lower single phase voltage, two phases
must be coupled and complete phase redundancy thus is not possible.
PRIMERGY BX600 S2 Basic Unit
Connecting the System to the Mains
165).
47