Power distribution units, or PDUs, are a necessity for distributing power to active network equipment in racks and cabinets located in the data center or telecom room. They come in a variety of sizes and flavors to ensure the right input and output voltages, amount of power, and type of receptacles required by your critical network equipment. PDUs can also protect your equipment—everything from real time monitoring of power usage at the rack level or outlet level, to controlling outlets for restarting or shutting down specific equipment and providing automatic event notification of power events that can put your network at risk of downtime. They can also help you achieve power usage effectiveness (PUE) for efficiency and cost savings. But how do you know which PDU is right for you? Let's take a closer look.
Know Your Specs
First and foremost, you need to know what voltages your devices require. They could require 120 V power, or they could range from 200 to 240 V power. Most data center equipment today, including servers and switches, are designed to accept any voltage, but larger servers tend to be configured for 208 V for greater power capacity. Severs also draw less current at 208 V than at 120 V, which means they'll produce less heat and run cooler, cutting down on cooling costs and reducing risk of failure.
You also need to determine the type and number of plugs of the equipment and choose the correct receptacle type. In North America where 120 V is common, NEMA 5-15R or 5-20R are the most common receptacles and likely what you'll need. The NEMA 5-15R is the two-pole, three-wire grounding receptacle that most of us are quite familiar with as the standard household plug. It has a maximum current rating of 15 Amps. The NEMA 5-20R receptacle has a T-shaped neutral hole and has a maximum rating of 20 Amps for equipment that has a higher power draw such as computer room air conditioners (CRACs)—or the refrigerator in your kitchen. IEC-320 C13 receptacles are typically the other choice when it comes to PDUs. IEC-320 C13 connectors are used throughout the world and very common on PCs and AV equipment. Adapter cords can be used to bridge the two types together for plugging NEMA 5-15 plugs into IEC-320 C13 receptacles and vice versa.
The next step is to make a decision between rack-mounted horizontal PDUs and vertically mounted PDUs. Due to their size, horizontal PDUs typically have fewer receptacles – typically up to about 16 depending on how many rack units and if the PDU has both front and rear receptacles. Vertical PDUs on the other hand can typically accommodate upwards of 30 receptacles. So the decision here really comes down to two factors—how many receptacles you need in the cabinet and how much rack unit space you're willing to give up. Vertical PDUs are mounted within the cable management space to the right and/or left of the equipment so they don't occupy any rack units. Many rack-mounted PDUs can also be mounted in the vertical space if rack unit space is an issue.
Determine Your Level of Protection
Once you've determined your voltage, the number and type of receptacles, and whether you need a horizontal or vertical PDU, you need to define your level of protection. If you don't need any monitoring or control, you may only need a basic unintelligent PDU that just simply distributes power. Basic PDUs are a reliable and cost-effective way to distribute power to network equipment and are well suited for smaller spaces and less mission-critical equipment. However, most data centers can better protect network equipment, optimize energy usage, and support equipment and capacity changes by going with a PDU that offers more intelligence.
If all you really want to know is how much power is being consumed, a metered PDU might be the right type for you. The current draw for the connected equipment is displayed in amps in real time on the PDU's LCD display. This information is helpful when plugging in new equipment to ensure that it doesn't draw too much power and cause the circuit breaker to trip. It's also helpful for ensuring that power loads are equally balanced between redundant A-B power. Ideally, you don't want the combined current of both circuits to exceed 80% of the individual circuit's rating.
A step up from metered PDUs are monitored PDUs that allow you to monitor power loads, input voltages, outlet status, and other information remotely via an Ethernet network connection and management console software. This is especially helpful in a data center environment that needs to determine which equipment is using the most power or to monitor usage across several PDUs to prevent overloads and optimize load levels. With event logging capabilities, monitored PDUs also enabling reviewing history of power conditions for analyzing trends and making informed decisions about where to locate equipment, how to reduce power consumption, and how to optimize cooling. Monitored PDUs are also ideal for spaces where PDUs are not easily accessible or in unmanned environments like an edge data center. Monitored PDUs also have the capability of setting alarms based on user-defined thresholds and often include additional ports for attaching environmental sensors that allow you to remotely monitor temperature, humidity, or other information at the cabinet level.
While the ability to remotely monitor load and outlets is ideal for protecting equipment and improving overall PUE in the data center, you might also want the ability to remotely restart or shut down a piece of equipment. If so, switched PDUs are right for you. Switched PDUs offer individual outlet control at the PDU or remotely via an internet connection, either on demand or at programmed times. The ability to remotely turn outlets off and on allows for remotely rebooting frozen equipment, performing planned power cycling, and for turning off equipment that does not need to be running at certain times and drawing unnecessary power. This can be especially useful during power outages as it allows for shutting down unnecessary equipment to extend runtime on more mission-critical loads. Like a monitored PDU, a switched PDU also offers event notification for user-defined thresholds and is supported by management console software.
Now that you know which PDU is right for you, don't forget about support. Some subpar PDUs on the market only come with a one-year warranty or less and limited customer service. The good news is that not only does Cables Plus USA offer a complete line of basic, monitored, metered, and switched PDUs in variety of sizes and with either NEMA and IEC style receptacle, our PDUs also come with a three-year warranty and the superior customer service you've come to expect. Just contact us at firstname.lastname@example.org or 866-678-5852 for more information.