Power Distribution Units (PDU's)

Power distribution within the server room or data centre is one of the most important decisions when designing the Server Room. The PDU style chosen will ensure ease of power management to servers and IT equipment within the server cabinet and will optimise the available space. The cabling management can also ease fit-out, upgrades and general maintenance.

The monitoring provided by a metered or intelligent PDU will assist with load balancing and understanding the equipment's power usage during all periods during the day and night. Analysis of data produced in particular with the more intelligent PDU will improve energy efficiency and help identify issues with cooling such as hot-spots and other environmental concerns.

Power distribution units (PDU’s) are units with output sockets fitted in a metal casing with an input lead to deliver power from an external source to the sockets. They come with brackets to allow horizontal 19” rack mounting or, particularly with larger sizes, vertical mounting within the Rack to provide power to the equipment connected to the PDU power outlets.

PDU’s are a critical element in designing the power distribution and protection of equipment within the server rack. 

PDU input power is supplied by an Uninterruptible Power Supply (UPS) system, or a distribution switchboard, installed in the Rack or externally within the room or building. The PDU's can be connected to the UPS's output with a suitable plug, or hard wired to an external board. 

We need to understand the PDU types and decide which are the most suitable for a particular situation.

Types of Power Distribution Unit

There are three main types of power distribution unit: Basic, Metered or Intelligent, and can be supplied as single-phase or three-phase. Depending on load requirements, the PDU's are wired with either 16Amp or 32Amp power cable.

The PDU’s can have different socket types such as UK, IEC, Schuco etc. either as single type or mixed type (known as Hybrid socketed PDU’s).

You can specify the IEC outlets with locking sockets to prevent inadvertent removal.

Basic PDUs

A basic PDU is similar to a standard extension lead fitted with several power sockets in a self-contained housing with an input power lead and plug, providing simple power outlet connection and distribution.

This PDU type may be connected to a mains power supply or a UPS outlet. The PDU can be unswitched, or in some cases, the output sockets can be individually switched and individually fused. Basic PDU’s can also have Surge and Filter protection, and overload breakers fitted. The basic PDU is most suitable for small computer and server rooms and remote floor or wall-mounted distribution racks with limited power requirements. 

Metered PDUs

A metered PDU is more sophisticated than a basic PDU. These can have either a dual display Digital Ammeter, displaying incoming Voltage and Current usage or a Digital Power Meter showing Amps; Volts; Watts; KHz; and Power Factor. Pressing a button enables cycling of the readouts on display. Metered PDU’s can have alarms to warn on overloads and other critical alerts. You can integrate these alerts into Data Centre Infrastructure Management (DCIM) software allowing remote configuring and monitoring of the PDU's overall power and energy usage over a web interface or SNMP. IT managers can easily balance their power loads and protection, ensuring circuits are not overloaded or have unauthorised devices plugged in, as the loads change in real-time if a new network device is connected.

These metered PDU’s are monitor PDU's recommended for larger server rooms and data centres. The information collected is ideal for detailed analysis of consumption, to produce accurate billing of shared resources in a co-location data centre.

Intelligent or Smart PDUs

Intelligent power distribution units (iPDUs) are a much more sophisticated version of a metered PDU. They are IP networked devices used to increase the operational efficiency and Eco management of server rooms and datacentres. They achieve this with intelligent monitoring and control features using an inbuilt web browser and SNMP and DCIM software integrated with the metered PDU, allowing precise control of power and energy management.

Monitoring is possible down to individual sockets along with the ability to power down or reboot a single socket. Additionally, sequential start-up of sockets, where equipment is needed to switch on in a set order, is an important feature allowing remote powering down and rebooting of servers.

iPDU’s can provide remote on/off power control for individual sockets to disable unused sockets preventing accidental load connection. User-defined power boot sequencing, auto power on to reduce surge currents, and security with assigned access credentials, to avoid unauthorised power access, is also a feature of iPDU's.

iPDUs can be enhanced to allow group configuration and firmware updates from a centrally controlled Data Centre Infrastructure Management (DCIM) software.

iPDU’s will generally have built-in USB-C ports, Gigabit Ethernet connection ports and interactive displays to show power and energy information across the phases (on 3 phase units). Additional sensors are easily fitted to the iPDU to give temperature and humidity and security monitoring for water leakage, smoke, fire and access control.
iPDUs can have colour coded individual sockets and circuit breakers to identify A and B supplies, lockable power cords can also add extra protection to connections.

Using switched iPDU’s is vital in large server rooms and datacentres due, not only to, the detailed information provided for capacity planning and the ability to monitor and control loads in real-time, to them allowing Network Managers to remotely manage servers and other IT equipment powered from an iPDU over extensive and even off-site remote installations. 

Remote switching is also far safer than entering a densely packed rack cabinet to switch or disconnect power cords manually. An iPDU is always the preferred option and is essential when multiple or remote sites need managing from a central location. Choosing the best solution for your server room can have an enormous impact on overall power reliability, monitoring and control thus contributing towards environmental, energy efficiency and management of the critical loads themselves, resulting in not insignificant lower costs of ownership.

Custom PDUs

A custom PDU is one built to your specification. These are commonly requested and done as it is often more economical on space, and cost, within a cabinet to create a PDU with multiple socket styles and meters with just the one Power input lead than it is to have separate PDU's for each type required. Options include socket-outlet arrangements and types, power ratings such as 16A or 32A plug type and power cord length.

Things to Consider when Selecting a PDU

  • Do you need single or three-phase power?
  • How many power outlets do you need? Every device within your server rack or racks will require a power source. 
  • What type of sockets do you need?  Most IT devices will have IEC C14 (10Amp) or IEC C20 (16A) plug cables to power them. So you will need a PDU with either IEC C13 (10A) 0r IEC C19 (16A) sockets or a combination of both socket types, known as a Hybrid PDU. It will likely be necessary to add UK (BS1363) style sockets to the list. Sometimes it may be a requirement to have either European CEEE or US sockets – this can easily be done. 
  • Do you require surge/filter protection?
  • Do you need lockable C13 or C19 sockets? 
  • What is the overall power load? A PDU should be rated for the load to be powered, and include a safety margin of 10-20%. The socket type and internal wiring determine the maximum power drawn from the socket and any overall protection such as a circuit breaker to prevent damage from an overload or power surge. 
  • How will the PDU be mounted in the cabinet? You can install smaller PDU's horizontally within a 19" rack, usually, up to 12 x C13 sockets or 6 x switched or 8 x unswitched UK Sockets in the space of 1.5U. PDUs with many power outlets are too wide for this arrangement and require a vertical mounting.
  • What are the metering and control options required? None – select a basic PDU, local power monitoring – select a metered PDU with a digital display either a Volt/Amp meter or a Power Meter – depending on requirements. Remote and Local Power Monitoring – select a metered PDU as above with additional monitoring software. Remote and Local Power Monitoring and Socket Switching – select an intelligent iPDU

You can find out about the range of PDU's available from CMW by clicking here. You can also speak to the team by emailing sales@cmwltd.co.uk