Live Voltage: Power Distribution In The It Rack

IT professionals use power distribution units (PDUs) to power the servers installed in the rack and the network components. These are high-quality multiple sockets, fused according to current industry standards, which can be optionally provided with intelligent performance features. PDUs can measure power consumption and trigger alarms or actively switch during an emergency. Sensors can optionally determine the temperature or monitor access to the IT rack.

Depending on the design involved, PDUs can monitor and control the power supply down to the individual outlet. The devices support remote maintenance, are network-capable and provide important functions for optimised energy management in IT environments of any size. PDUs are a central component in setting up an IT rack, as they supply the power needed for all the IT equipment installed. When selecting a PDU, the space in the IT enclosure first has to be noted. The PDUs are ideally mounted in the zero-U-space – in other words, in the space between the mounting frame and the 19″ mounting frame. This way, no height units are blocked, and maintenance and installation work is still possible, even with a fully configured IT rack.

How much power is consumed?

Another selection criterion is the power that the PDU has to distribute. The simplest variants come as single-phase models staring from 16 A, with a distribution capacity of 3680 W. The higher currents, of three phases, are intended for 32 A outputs. This means that a power of more than 22 kW can be fed into an IT rack.

PDUs offer several variants for energy monitoring. For smaller installations in particular, it may make sense to choose devices that have displays. In such cases, less technically skilled staff can also read off the current status from the outside. Alternatively, automatic notification via text message or e-mail is, of course, possible when limits are exceeded.

Safeguarding energy supply

To achieve a high level of reliability, the energy supply in the IT-rack should be set up with redundancy, via an A/B power supply with two identical PDUs. At this point, implementation does call for a little forward planning as dual power cabling is needed. In particular, where the rack is populated with mixed IT components, wiring must be planned in advance so that efficient maintenance will still be possible in the future.

Connection wanted

In Germany, safety plugs (earthing-pins) as per CEE 7/4 standard (Type F) are still frequently used in data centres. These are of very robust design and the high insertion forces involved prevent the plug from being accidentally pulled out. Today however, the use of internationally common IEC 60320 C13/C14 and C19/C20 connector systems is recommended in IT environments. This way, a considerably higher packing density and a higher number of sockets can be achieved. Modern PDUs make it possible to protect these connectors against accidental unplugging by locking them. Ideally, the locking mechanism is vendor-independent and allows the use of existing server connection cables.

The IT enclosure is finally connected to the mains via a CEE three-phase connector or Cekon plug: There are red connectors for three-phase alternating current with neutral and protective conductors and a rated voltage of 400 V, as well as blue connectors with only one external, neutral and protective earthing wire for a voltage of 230 V.

Remote maintenance via the PDUs

Administrators can make remote maintenance easy by using intelligent PDUs. If an IT rack is difficult to access, for example, or if the system also has to be maintained at the weekend, a PDU with switchable connectors is very helpful, since individual sockets can be remotely switched. At the time of purchase, one should always make sure that any slots are arranged in groups so that multiple devices or the A/B power supply can be switched off with just one click. Another tip for saving energy: where possible, use PDUs with bistable relays. These remain at zero current in their respective switching state, so reducing the internal consumption of a PDU to less than 15 W. This way, energy costs can be perceptibly reduced, especially during 24/7 operation.

Security and access protection

Additional security features are needed if intelligent PDUs are used. To this end, modern variants integrate directory services such as Active Directory by Microsoft, Lightweight Directory Access Protocol (LDAP) and Radius to authorise individual users. The information collected by the sensors, such as temperature or humidity data (or whether an enclosure door is open) is forwarded by PDUs via standard protocols. These details are received by DCIM (Data Center Infrastructure Management) software for the IT management or facility management-based control stations.

Linking the PDUs

PDUs are linked up with a standard Ethernet port and protocols such as IPv6 (Internet Protocol Version 6), SNMP (Simple Network Management Protocol), Modbus (a communication protocol based on master/slave or client/server architecture), TCP (Transmission Control Protocol) or OPC-UA (Object Linking and Embedding for Process Control Unified Architecture). Wireless procedures should not be used because Wi-Fi signals could disturb the sensitive IT systems. In order to control the PDUs in the event of a supply voltage failure, they should optionally receive current via Power-over-Ethernet (PoE).

Alternative: modular PDU systems

Rittal offers modular power systems under the name Power System Modules (PSMs). These are constructed as vertical support rails with three-phase supply, and the necessary modules with sockets or additional functions are simply snapped on to them. For example, Rittal offers a modular PSM system with a variety of features similar to the PDU portfolio: for measuring, switching or monitoring. The advantage of these high-quality solutions: the opportunity for flexible and individual configuration. Anyone who operates a constantly evolving data centre and regularly reconfigures IT racks has the right solution in the Rittal PSM.