The Ultimate Buyer's Guide for Purchasing Electrical Distribution Equipment

Understanding PDU Meaning and Why Choosing the Right PDU Matters

Ensuring consistent, reliable power for all the mission-critical equipment in your data center is no small feat. You know that a backup or uninterruptible power supply (UPS) is essential in this effort. However, it’s not enough to have power available. You also must be able to reliably distribute the power to your various equipment. That’s where a power distribution unit, or PDU, comes into play.

While a PDU serves the vital function of being the last link of the chain in your overall power infrastructure, many data center personnel are a bit fuzzy on PDU meaning. In its most basic sense, the role of the PDU is to reliably distribute AC power to multiple servers or other IT equipment in the data center. In many ways, a PDU works a lot like a multi-outlet surge protector or power strip. However, today’s PDUs include features and capabilities that would put even the fanciest power strip to shame.

What Are the Main Types of PDUs?

Before you can determine the right PDU for your application, it’s a good idea to get familiar with the different types of PDUs on the market. While some enterprise or hyperscale colocation data centers make use of large power distribution units capable of distributing power to entire rows, such as the NetSure series, most data center applications require rack PDUs (or rPDUs).

These rack-level devices can be either basic or intelligent, and can be split into four main categories:

• Basic rPDUs deliver reliable power to critical IT equipment within a rack or cabinet. They are the most similar to your common power strip, and they provide a cost-effective, entry-level solution. Some models offer features like locking receptacles to prevent accidental disconnection of equipment, as well as the ability to add intelligence or smart capabilities in the future. Basic rPDUs are a good option for small server rooms where IT staff is on site, since they cannot be remotely managed or monitored.
  
  
• Metered rPDUs provide reliable power distribution along with a real-time view of power usage from a local LED display. Data center personnel can use the display to keep tabs on key power utilization metrics including current, voltage, and power factor, which can help with capacity planning and electrical load balancing. This type of rPDU is a good choice for highly secure data center environments with dedicated IT staff on site. Metered rPDUs are also a nice steppingstone for facilities that foresee an eventual need for remote monitoring.
  
  
• Monitored rPDUs are one type of intelligent or smart rPDU. They go a step beyond metered rPDUs to offer remote monitoring capabilities over the network. Data center employees can remotely access real-time power consumption metrics down to the outlet level and can receive alerts when user-defined thresholds are exceeded. These devices typically include optional environmental monitoring capabilities to obtain real-time environmental metrics in addition to the power metrics. The use of this information helps with reliability, limiting stranded power, and billing accuracy. Monitored rPDUs work well in high-density data centers including large colocation facilities that need to better understand what percentage of power is being used by which customers.

• Switched rPDUs offer the highest level of smart capability, making them the most intelligent rPDUs on the market. They do everything monitored rPDUs do with the added benefit of individual outlet level control. That means that authorized data center personnel can turn on, turn off, or reboot unresponsive equipment from a remote location using an intuitive web interface. They can also limit power usage at the outlet to avoid accidental overloads. These features combine to provide the ultimate solution for control over data center power usage, efficiency, and availability. This control can be equally important for large-scale data centers as well as small, remote, or edge locations that lack an on-site IT team.

5 Questions to Ask Before Choosing a PDU

Now that you have a better understanding of PDU meaning, you can begin to narrow down the choices and select the best rPDU for your unique application. Start by asking the following questions:

1. What are the power requirements for your critical IT equipment? Calculate the approximate kilowatts (kW) needed for the equipment installed or that could potentially be installed in each rack. To ensure you have the flexibility to scale your data center over time, consider your expected growth needs. It is a good idea to plan for more power than you need right now so you have the room to grow.

 Once you have the kW requirements, you’ll need to choose a rPDU that  supports the appropriate phase (single-phase or three-phase) alongside the amps and voltage required.

2. Do you have the rack space available for the rPDU? Rack PDUs come in both horizontal and vertical (zero U) designs. Horizontal rPDUs typically require 1U to 2U of space in a standard 19-inch equipment rack. If you need to keep your rack space free for other equipment, a vertical rPDU may be the better choice. Vertical units can be mounted on the upright rails of the rack enclosure, so they do not take up critical equipment-mounting space inside the rack. 
   
   
3. How many and what type of outlets do you need? Horizontal rPDU units usually offer between eight and 16 outlets while vertical-mounted rPDUs can have up to 54 outlets. When calculating the number of outlets you will need, be sure to account for equipment beyond your servers, such as lights and cooling fans. Always be sure to keep future growth in mind.
   
   You also need to think about receptacles and the types of plugs your      devices have. A rPDU that offers combination outlets gives you the flexibility to connect different types of plugs in the same receptacle, which can help ensure future-ready infrastructure as your equipment configuration needs evolve over time.

4. What additional features will support your power goals? There are no shortage of bells and whistles on today’s rPDUs. Think through what’s most important in your environment. Some of the most popular options worth considering include:

Alternating outlets with color coding. To simplify circuit/phase balancing and cable management, some rPDU manufacturers offer color coded alternating outlets that significantly streamline the deployment process while helping to prevent overloading circuits or stranding power.

Locking outlets. Outlet locking mechanisms secure the physical connection between the IT equipment and the PDU to ensure power cords are not accidently pulled out of the outlet, causing an inadvertent load drop.

High temperature grade. A high temperature grade rPDU should be considered in high temperature environments to ensure reliability and availability in power distribution. Depending on the manufacturer, rPDU maximum operating temperatures can range from 45 degrees Celsius up to 60 C.

Hot-swappable monitoring devices. Some upgradable basic rPDUs and intelligent rPDUs offer the option of easily updating monitoring devices to leverage new technologies and accommodate changing business needs without having to replace entire power strips or interrupt power to critical servers. This is great way to make your power distribution equipment purchase future-ready.

IP aggregation. Data center managers can reduce the cost of deploying intelligent rPDUs by choosing units with IP aggregation capabilities. Other features like IP aggregation with self-configuration of downstream devices can also significantly reduce deployment time and costs. 

Out-of-band communication. If the primary network to the rPDU goes down, some rPDUs provide redundant communications through integration with out-of-band management devices, such as serial consoles or KVM switches. 

5. Are you looking to standardize across global applications? Companies that operate data centers around the world often struggle with the extreme diversity in worldwide electrical standards and compliance requirements. This can make it difficult to standardize power distribution equipment, leading to SKU sprawl and additional supply chain costs and complexity. Companies like Vertiv are solving for this problem by introducing universal power distribution units that can work around the world to simplify global deployments.
   
   

Rack PDUs Available From Vertiv

Vertiv offers an extensive portfolio of standard rPDUs for all IT applications, ranging from the reliable and cost-effective Basic rPDUs to the robust monitoring and control offered in the Switched rPDUs. Every unit is 100% tested for reliability and functionality and comes with a warranty for peace of mind.

 A few of our most popular products include:

Vertiv™ Geist™ Basic Rack PDU. This basic rPDU combines reliable rack power distribution with simple and convenient configuration options for cord lengths and chassis colors. 

Vertiv™ Geist™ Metered Rack PDU. This upgradeable metered rPDU gives instant access to power consumption metrics on the local digital display and features hot-swappable technology so that it can be easily converted to an intelligent monitored rPDU.

Vertiv™ Geist™ Monitored Rack PDU. A smart rPDU, this model offers both local and remote power monitoring option along with optional environmental monitoring. It can be used with the Vertiv™ VLC mobile app to put comprehensive power and environmental data in the palm of your hand.

Vertiv™ Geist™ Switched Rack PDU. This intelligent model puts complete power distribution control in your teams’ hands with local and remote monitoring and control. This includes the ability to remotely reboot outlets to power cycle unresponsive IT equipment or increase runtime of critical equipment upon power failure.

If you want to learn more, please visit our website Electrical Distribution Equipment.