Power Distribution Unit
How To Choose the Right Power Distribution Unit for Your Data Center IT Enclosure
August 19, 2020 / by Rittal Marketing

Powerful Solutions to Electrical Power Distribution Questions

The PDU: no longer just an ordinary power strip. Today, among the many important decisions when it comes to data center efficiency, is which rack mount power distribution unit (PDU) to use. Simply put, rack PDUs transform raw power feeds to lower-capacity outlets for use by switches, servers, storage systems and related appliances. The power demands (and associated connectors) within a single rack will vary, making the job of the PDU to distribute the right power to the right equipment more complex. This makes selecting the right PDU for the enclosure a bit more complicated.

And then there are configuration choices: Options start at very basic PDUs that perform a pure distribution function, to more sophisticated PDUs that offer features that make IT Managers’ lives less stressful and more productive.

Types of Server Room Power Distribution Units

A Basic (or standard) PDU features a fixed number of receptacles (NEMA or IEC) and simply gets AC power from a UPS system, generator or utility source to connected devices. The basic PDU is a very short step up from the legacy power strip – just a single case housing a single receptacle type in limited numbers. No intelligence, no flexibility, and very limited circuit protection. Maybe just a few more receptacles and supply power plug types than on a plug strip you can pick up at the local hardware, office supply, home improvement store.

More advanced PDUs do far more than simply supply AC power. Intelligent PDUs provide a more complete range of capabilities. Smart PDUs measure critical metrics such as current, voltage, and both overall power consumption and that of individual devices. Most provide networking capabilities for remote monitoring and operational reporting. The most advanced systems will even provide control and monitoring at the individual receptacle.

  • Metered PDU. A step up from a basic PDU, the metered PDU allows users to locally see, in real time, the current/load meter so that action can be taken when the PDU is close to the point of overload. This capability helps avoid downtime and ensure that your most critical equipment is available during power outages
  • Monitored PDU. A monitored PDU allows data center staff to more precisely manage, control and quickly react to situations. A digital meter display allows for both local and remote monitoring, and the networking capability in many monitored PDUs enables you to activate and deactivate single branches. Energy consumption of each connected device can be monitored so that downtime due to overloads or other power events can be minimized. Integrated measuring systems make it possible to monitor and record all relevant parameters of the system, and to define limit values for the current, voltage and power per phase of the infeed – if any value is exceeded, the system sends an alarm by e-mail or SMS
  • Switched PDUs employ a digital meter to provide information on load and voltage, and use one of several network protocols to enable users to remotely control outlets individually or collectively, so you can reboot equipment from any location without having to physically be on site. Another advantage of the switched PDU is the ability to configure the unit so that it can automatically shed loads during an outage. During a power failure, for example, a switched PDU connected to a UPS system could be programmed to power off your least important equipment first and preserve battery backup power for mission-critical systems

(Please note PDU manufacturers may have different names or definitions functions described above)

Types of PDU Systems

Modular. The basis of a modular system is a support channel that acts as a backplane and is connected directly to the power infeed or UPS system. Socket modules of different types can be mounted on the support rails as needed, making it a flexible way to address changing power demands, and a very attractive option when a skilled staff isn’t readily available, as modules can be switched out or added easily without any special training. In Rittal modular systems:

  • The backplane/support rail accommodates all cabling, providing for full shock-hazard protection; socket modules themselves are closed systems and provide the same protection. This makes it possible for staff without electrical knowledge to work with the modules
  • The backplane can be mounted vertically on the frame, so that no rack units are occupied, maximizing available equipment space
  • Two independent infeed sources – 3-phase and single-phase – allow for redundancy within a single backplane and reducing enclosure costs

Network-capable. With network-capable systems, the intelligence of the socket modules is independent of the backplanes, allowing you to combine intelligent or active modules with passive modules on a standard backplane. This is useful when only some of your installed equipment needs to be monitored and controlled. The sockets on active modules can be switchable, so connected devices can be controlled individually; they also allow you to define limit values and allow for alarm messages to be issued via e-mail or SMS.

Because they allow for power distribution to be adapted to different circumstances, modular and network-capable power distribution systems provide much-needed flexibility and scalability, and help reduce overall energy consumption.

How To Choose the Right PDU for Your Data Center

The two primary factors influencing the choice of PDU are location and staffing.

  • Large facilities. If yours is a large facility with hundreds of server racks, your focus is undoubtedly on minimizing costs and maximizing floor space. In these data centers, power consumption is being continually monitored at many levels, so you may not feel the need to also monitor the PDU; you could actually save money by deploying basic or metered PDUs. However, switched PDUs do allow you to remotely reboot equipment, reducing downtime and minimizing stress on your staff
  • Small facilities. If you’re deploying the PDU at a branch location that is not staffed by local IT personnel, a monitored or switched PDU, while more costly up front, will save you money in the long run because you will not need to send IT staff to the site when power needs to be restored. With some switched PDUs, you can break down power consumption at the outlet level to get details about how much power a single device is pulling, a feature that helps troubleshoot problems as they occur

And finally: Remember that regardless of what type of PDU is selected, there must be sufficient installation space in each cabinet to support them. And not just one PDU; the most common configuration will use two PDUs, fed from two separate power supplies, installed in the rear section of the cabinet. Installation depth is critical, especially in a 24” wide cabinet supporting deep (>34”) appliances. Even if you think there is enough room back there, don’t forget all the cables with their plugs – you will need that much more room to make sure everything fits and you can close the back door.

Every data center – and, more specifically, every data center IT Manager and Facility Manager – is under pressure to manage power as efficiently as possible, and PDUs play a critical role in how successful they are in doing that. Beyond just the basic delivery of AC power to equipment, the right PDU allows users to monitor and control power and, in turn, optimize power consumption and maximize uptime.

Rittal’s power distribution solutions aren’t the only reason we are the world’s leader in modular IT solutions. Innovative, efficient cooling technology is another, and you can read more about the best ways to remove heat from your data center by reading our High Performance Cooling Whitepaper – a valuable resource for any data center professional looking for the highest level of efficiency.

-Herb Villa, Rittal Sr. Applications Engineer
High-Performance-Cooling-White-Paper

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