Rack Power Distribution Units (rPDUs) are the last link in the power chain and ensure delivery of critical power to IT loads. The rPDU is designed to distribute power to all types of IT equipment within the data centre.

The rPDU does not generate power but rather distributes power from the power source available. In a typical data center environment, the rPDU is connected to an upstream Power Distribution Unit (PDU) commonly referred to as a floor PDU. The floor PDU distributes power from the utility during normal operation. During an outage, an uninterruptible power supply (UPS) picks up the power load while the generator ramps up to begin providing power to the facility. The floor PDU is similar to the circuit breaker panel in your home and breaks down the available power into circuits so electricity can be distributed throughout the facility. The generator is used for redundancy in case utility power is lost. Power is distributed through the facility from the floor PDU, and the rPDU is connected downstream. The rPDU then distributes power to the IT equipment in each individual cabinet and rack.

The rPDU is capable of monitoring, managing, and controlling power consumption to multiple devices in data center environments. It can distribute large amounts of electricity and can be accessed over the local network or remotely. To meet the ever-changing needs of the data center, rPDUs can accommodate higher power densities and are resistant to higher temperatures. To avoid compromising basic power distribution, some rPDUs are easily upgradeable and serviceable without the need to remove power from the connected devices. These features minimize downtime and carry manufacturer-provided support to meet Service-Level Agreements (SLAs).

Why is a Rack PDU important?

As data center environments become more dynamic and complex, many organizations are putting pressure on data center managers to improve availability while reducing costs and boosting efficiency. Next generation high density servers and networking equipment have increased the demand for higher rack densities and overall facility power requirements. While densities under 10kW per rack remain the norm, deployments at 15kW are typical in hyperscale facilities – and some are even nearing 25kW. High density configurations provide improved levels of performance and capacity, but this creates the need for more effective power delivery. As a result, the features and functionality available on an rPDU become increasingly more important to achieve efficient power distribution to respond to changes in data center capacities and densities.


Selecting a Rack PDU

When selecting your rPDU, begin with these basic questions:

Power Requirements

The most important question when selecting an rPDU is determining the power requirements needed for the critical IT equipment that will be connected. Depending on the data center, the data center manager may be limited to the power available. While in other situations, the data center manager may be able to dictate what power is delivered to the rack. If the data center manager has the ability to decide the power available, he or she should determine the approximate kW needed for the equipment that is or will be deployed. The power needed will provide the minimum power required for the equipment in the rack allowing the data center manager to appropriately determine the rPDU power configuration needed. The data center manager will then be able to have an electrician pull the necessary power with the appropriate receptacle to the rack that matches the rPDU.

On the other hand, if the data center manager is restricted to the power that is already available, he or she will need to identify the receptacle type the rPDU will need to plug into. Depending on the power available, the cabinet density could be limited or additional rPDUs will need to be deployed in the same cabinet to reach the power capacity required for the deployed equipment.

Power Configurations

There are numerous rPDU power configuration options and what is available will differ depending on the global region the units will be installed. Different amperages and voltages as well as single-phase and three-phase power options are available. Data centers could have single-phase or three-phase power distributed throughout the facility. Single-phase power is more commonly used in homes and small businesses but can also be distributed in data centers from a three-phase power source. Many high-density data centers distribute three-phase power throughout the data center as it is more efficient and supports higher densities.

Determining what is best depends on the power available and power needs of the equipment connected. The rPDU is available with different power (100V single-phase to 240/415V three-phase) and current rating (10A to 120A) options.

Horizontal Mounting vs Vertical Mounting

Rack PDUs are mounted horizontally or vertically, inside or outside the rack enclosure. Horizontal rPDUs are installed inside the rack and take up space, typically 1U or 2U rack space and have 8-16 outlets. The vertical mounted rPDUs can hold up to 54 outlets. They are installed at the back or side of the rack enclosure so they do not take up critical equipment mounting space inside the rack. Understanding your data center space and IT equipment before selecting the mounting option for the rPDU can help save cost, time and space.