IT equipment evolves dramatically every three years. The newly developed technologies require more power to run heavier workloads, as server equipment further evolves. At first, data centers used Single Phase power which uses 1 hot wire, 1 neutral wire and 1 ground wire to supply 120V. As the need for more power increased, data centers then shifted to Split Phase Power which uses 2 hot wires,1 neutral wire and 1 hot wire to supply 240V. By now, servers maintain so much data that most data centers have moved to 3-Phase power which utilizes 3 hot wires, 1 neutral wire and 1 ground wire to power a circuit with 208V. 3-Phase power, unlike Single Phase power, is able to provide equipment with a constant stream of power and is able to power much more advanced IT equipment.
The Universal Benefits of 3-Phase Power
Even though 3-Phase Power is used to power advanced devices, that doesn’t mean that older devices have become obsolete, and have to be upgraded immediately. Older equipment that was previously powered by Single Phase or Split Phase Power can still be powered with 3-Phase Power. A cord that previously supplied 120V to the device can be switched out with a new cord to plug into the 208V power. This cord has an IEC C13/C19 plug on one end that plugs into the actual equipment, and an IEC C14 or C20 end that can be plugged into the Power Distribution Unit (PDU). Thus, 3-Phase Power can universally accommodate powering most IT equipment. It should be noted, however, that before switching the original cord to a new cord, a device should be checked to make sure that it is compatible to run on 208V, as some devices are not able to use a higher voltage source.
The Issues of Load Balancing 3-Phase Power on a Traditional PDU
3-Phase Power uses three different branches of circuits: the XY circuit, the YZ circuit, and the ZX circuit. The three different branches have outlets that are clustered together in a per branch basis on a traditional Power Distribution Unit.
Because of this design, 3-Phase power requires load balancing the Power Distribution Unit where the current draw on each circuit is balanced to match the other circuits, in order to achieve the highest capacity density possible. It is easier to load balance if a rack contains only one style of server equipment, but as servers have evolved, many racks contain multiple styles of server equipment, which becomes more difficult to balance. If an installer starts plugging in equipment from end to end of the PDU, it is possible to fill two of the three circuits and leave the third circuit with stranded power. Essentially, a fully loaded rack that hasn’t fully utilized the power draw on the third (ZX) circuit but has maximum capacity density on the other two (XY and YZ) circuits is unable to power any more equipment, regardless of empty outlet spaces. This stranded power, is a huge waste of money for the data center.
Furthermore, high and unbalanced loads on a single phase results in greater chances of tripping either the PDU or an upstream breaker, and losing power at the rack—which is worse from the cost perspective than having stranded power. Thus, equipment installers must use longer power cords to plug into different phases to balance the rack load, which can create a crazy mesh of power cables on the rack. The cables inhibit airflow, and adds to cooling costs. While load balancing is necessary on traditional PDUs, it is a huge inconvenience to the equipment installer.
Alternating Phase PDUs
Alternating phase PDUs are being developed, which provide a much more convenient way to use 3-Phase power when compared to traditional 3-Phase PDUs. These PDUs actually alternate power circuits on a per-receptacle basis as opposed to having outlets clustered branch by branch on the PDU. Traditional 3-Phase power PDUs use wires within the PDU to separate the three phases. One specific company, Server Technology has a unique patent pending PDU structure uses a multi-layer circuit board within it to separate the three phases. Each outlet contacts a different trace within the PDU, which then automatically distributes the power of the three power phases within the PDU.
These alternating phase PDUs have many benefits over traditional 3-Phase PDU’s. Because alternating phase PDUs are automatically balanced within the PDU, this eliminates the tedious planning of load balancing traditional required with traditional 3-Phase PDUs. The equipment installer no longer has to use longer power cords to reach another branch, but instead can use a shorter cord to plug into the next available outlet. That dramatically lessens rack assembly time and removes any margin of human error during load balancing because pieces of equipment can be powered by their order on the rack going from end to end. This improves airflow and reduces cooling costs incurred with traditional 3-Phase PDUs. Alternating phase PDUs will ultimately lead to more assured uptime and lower overall costs of maintaining uptime within the data center.