FAQs - Power Distribution

A basic power distribution unit (PDU) gives you multiple power outlets for equipment that’s installed in a server rack. This type of PDU is very similar to a power strip but one designed for installation into a standard 19inch server rack or cabinet. The PDU will typically have IEC320 outlets, some form of resettable circuit breaker and a fixed form factor for either horizontal or vertical mounting.

Metered PDUs go a step further by displaying information such as voltage, current and energy consumption. Intelligent PDUs offer more advanced monitoring and, depending on the model, conveniently allow individual outlets to be controlled remotely. Basic PDUs are often the right choice for smaller installations, while metered and intelligent models are better suited to larger server rooms and data centres with more complicated control requirements.

Regardless of the type you’re working with, most PDUs are powered form a local AC (alternating current) power source via a trailing lead.

You should start by checking the power requirements of the equipment you plan to connect. Bear in mind that a server’s rated power supply capacity isn’t always down to the amount of electricity it uses during normal operation; actual consumption can be significantly lower, depending on the workload. When it comes to accurate PDU sizing, it’s best to use measured power consumption if you can, while allowing enough capacity for peak demand and expansion in the future. If you need help calculating how much power capacity your PDU needs, our projects team can help you work through the calculations.

Yes, and this is a standard arrangement in many server rooms and data centres. The UPS provides backup power during a mains failure, while the PDU distributes that power to the individual servers and networking devices within the rack. It’s important to make sure the PDU, UPS and connecting cables are compatible and correctly rated for the equipment that’s being supported.

Using two power distribution units can provide additional power resilience, especially for servers that are fitted with dual power supplies. One PDU connects to the ‘A’ power supply and the other to the ‘B’ supply, and ideally, each of these is fed from a separate (protected) power source. If one supply fails, the other can continue supporting the equipment, as long as it has the capacity to.

Three-phase PDUs distribute electricity from a three-phase power supply, which means they are often the sensible choice for larger server rooms and data centres with high power demands. Unlike single-phase PDUs, they can spread electrical loads across three phases, helping to manage power distribution more efficiently and reduce the risk of overloading individual circuits. They require a compatible three-phase electrical supply and, where backup power is needed, a suitable UPS.

Outlet-level monitoring allows you to see how much power separate pieces of equipment are consuming, rather than relying on the reading for the entire rack. This makes it easier to work out which equipment is underused, plan additional installations and spot any unexpected changes in consumption. Some intelligent power distribution units also allow individual outlets to be switched remotely, which can be particularly useful when equipment needs rebooting but it’s difficult to find someone to attend the site.

With intelligent PDUs each individual socket is remotely monitored for power and energy usage and can be remotely controlled i.e. powered down or rebooted to provide total control of the connected load(s).

Good power management starts with choosing a correctly sized PDU and keeping track of what’s connected to it. Labelling power cables, maintaining an accurate record of outlet connections and monitoring electricity consumption can make maintenance much easier. For larger installations, intelligent PDUs provide additional information on power usage, available capacity and circuit conditions, which can help you plan upgrades, identify potential overloads and reduce downtime as far as possible.

Colour coding makes it easier to identify which power distribution units (PDUs) and cables supply the different equipment within a server rack. It’s a technique often used in installations with separate ‘A’ and ‘B’ power supplies, because keeping connections clearly labelled helps to prevent accidental disconnections during maintenance works. Using different colours for each power source also makes troubleshooting quicker and reduces the risk of human error, especially in larger server rooms and data centres where downtime could be a catastrophe.

As well as power distribution units we have specific in-line energy meters that can be installed between power sources and their connected loads. The in-line meters come with flying leads, plugs and sockets and provide a range of power related information including kVA, kW, power factor, voltage, frequency and kWh of energy usage.

Some of the metered PDUs, smart and intelligent PDUs we supply can be installed with additional plug-in sensors for temperature and humidity. The PDUs are connected to the local IP network and can report monitoring readings taken by the sensors.