Different rack mounted power distribution unit (PDU) products have many different product characteristics, rated power, and input/output cable connection types. Choosing the right rack mounted PDU is sometimes not an easy task, especially when one does not know the exact information of the devices inside the rack. The new trends, including virtualization, converged infrastructure (including accounting, storage, and networking), and high efficiency requirements, make it particularly important to consider how to select rack mounted PDUs comprehensively. This white paper outlines the selection criteria for rack mounted PDU products and introduces some useful methods to reduce downtime.
To select a suitable rack mounted PDU for a specific rack, it is necessary to understand the relevant information of the equipment in the rack, the power distribution status on site, and the requirements for other auxiliary functions. In most cases, we follow an “inside out” order to select rack PDUs:
1. Recognize the type and quantity of output sockets
According to the “inside out” approach, the first step in selection is based on the equipment used inside the rack. The equipment inside the rack is equipped with different types of sockets. The most commonly used types of sockets in data centers are the C-13 and C-19 sockets explicitly defined in the IEC60320 specification. C-13 sockets are commonly used in servers and small switches because they require larger current carrying capacity. Blade servers and large network equipment generally use C-19 sockets. Almost all modern servers, blade server chassis, and enterprise level switches can use C-13 or C-19 input sockets, depending on power consumption. Most devices that do not use C-13 or C-19 sockets can be classified into the following three categories: old devices, devices with single line access to 30A or above power, or other devices that use them, such as air conditioners, fans, and laptop charging devices equipped with local standard power connectors.
To select the appropriate output socket for rack mounted PDU combinations, the primary requirement is to understand the I devices operating inside the rack. The sockets in rack mounted PDUs should at least match the number of sockets required for each type of equipment in the rack to ensure that each device can be connected for power supply. Among the rack mounted PDUs selected by many operators in data centers, the number of different types of sockets equipped often exceeds the initial load, making it easier to reserve sockets for future equipment. Table 1 provides the number of sockets required for different equipment combinations under general conditions. The commonly used socket combinations provided by most manufacturers are (36) C-13 and (6) C-19 sockets, as both can meet the requirements of low-density and high-density equipment together. From the perspective of data center operations, this means that a single common rack mounted PDU can meet the needs of almost all racks in the data center. Selecting universal socket equipment can help ensure that rack mounted PDUs are in stock and available immediately when needed at any time. There are multiple ways to budget the maximum power required for each I rack. Once the power demand is acknowledged, suitable rack mounted PDUs can be selected to provide satisfactory power support for the loads within the rack.
2. Estimated distribution capacity
(1) Budget I: Power consumption status of internal equipment in the rack. When there is a high-power load on the equipment inside the rack, this method is generally used, such as enterprise level servers, blade servers, or high-speed network equipment. Because the rated power value on the equipment nameplate is based on the power consumption under full load conditions, this value is generally higher than the actual power consumption value used in practice. Under normal circumstances, servers do not operate at full capacity, so the power capacity value budgeted by this method is slightly saved.
(2) Some manufacturers, including Cisco, Dell, and HP, will provide online power calculators to assist in more accurate budgeting of power consumption values for specific equipment (such as the number and type of boards and drives). Schneider Electric’s “Data Center Power Selection Calculator” can accurately budget the actual power consumption based on specific modules and equipment.
(3) Estimate the maximum power level of rack I based on the overall utilization rate of the data center. For example, if a data center supplies 1MW of power to IT loads consisting of 100 racks, the estimated maximum power level for most racks is around 10kW. Compared to independently calculating the maximum power capacity of each rack, this method is simpler and more feasible. This method is generally used in various types of accounting application environments and is difficult to predict the required type of I equipment. The method of constraining excess servers in the rack by users to avoid reaching the maximum power level, and then completing the manipulation of the application environment. Data center power selection calculator developed by Schneider Electric provides specific guidelines for budgeting data center power scales.