Power Infrastructure for the Data Center part 2

The three phase cable in the building consist of five wires; three wires arz 3 phase wires (R,S,T), neutral and ground.the conversion between the three phase to single phase is done in the distribution boards.the single phase cable is consist of three wires; two of them are neutral and ground, the third wire is one of the phase power wires
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most data center UPS are based on three phase power although most IT equipment are based on single phase power supply. so load must be balanced between the three phase and the imbalance should not exceed more than 10-15 %.

the power cable routing for racks under raised floor must supply three phase socket from two sources for each rack. as single phase routing isn't recommended. in some countries racks isn't allowed to feed from three phase so each rack with IT equipment that has single power supply is feed from two phases. for dual power sources racks, the rack is fed from the same single phase on each source.

dual source should be routed to each rack. all conductors have the same size even the ground cable to get rid of the noise. neutral cable size can be doubled to withstand high harmonic and high imbalance between phases. each power rail should have its own breaker. use dual supply equipment where possible. use STS for single power supply equipment.
there are many level of availability for IT equipment we will start by the low availability:
the low availability happens when single ups feed the a single PDU and all IT equipment is fed from single source without STS. so a failure in UPS or PDU  will cause all system to shutdown.
there is a slightly better availability when two power rail feed the rack as it make a redundancy over the power rail for two power sources devices but any failure in UPS or PDU will cause the entire system to shut down.
there is improved availability option when two UPS's with two PDUs and two power rails is connected to the rack. the draw back is there isn't STS for single corded IT equipment so any failure in the source that feed these equipment will cause these equipment to shutdown.
the high availability option is done by feeding the single power corded IT equipment from STS and entirely  two independent power sources. and the two power corded IT equipment is fed from the two power sources directly. but if STS fail the single corded equipment will shut down.