When you consider all the options available, it can be difficult to know where to start, so here’s a quick guide to help you make the right decision when choosing a rack PDU.


IT equipment in a rack can have many different types of plugs. The most common connector types in data centers are C13 and C19 or Universal (UK) connectors. The C13 connector is commonly found on small servers and switches and is similar in appearance to the plug you might find on a home appliance like a kettle. While larger network devices use a higher amount of power, the C19 plug is used because of its higher current carrying capacity.

Choosing the right combination of sockets for a rack PDU starts with considering the IT equipment that will operate in the rack. Rack PDUs should have at least as many plugs of each type as the device inside the cabinet so that every device can be connected, remember that having too many outlets is not enough!
Many data center operators choose rack PDUs with more outputs of each type than is needed for the initial load. This allows additional outlets for future devices. A popular socket combination from several APC manufacturers is (36) C13 socket and (6) C19 socket because it allows for a combination of both high or low density equipment. From a data center point of view, this means that a single, common rack PDU can serve practically any rack on the floor.


Several methods can be used to estimate the maximum capacity required for each IT rack. Once power requirements are established, a rack PDU can be selected that provides at least enough power to support the rack load.

Estimate device power usage inside an IT rack. This method is often used when using very high capacity loads such as enterprise-class servers, blade servers, or high-speed networks. The nameplate rating on this device is often higher than actual usage because it is based on the draw of the power supply at full load. Servers are usually not configured to use the full power of the supply, so this approach is considered quite conservative.
Several manufacturers including Cisco, Dell, and HP offer online calculators that can more closely estimate actual power consumption for specific configurations (number and types of cards, drives, etc.). ). APC Schneider Electric Power Bars provide a sizing tool to help estimate actual power usage based on specific models and configurations, but if you’re still unsure you can always call us and We will be happy to help you with that.

Assume an IT rack’s maximum capacity based on an estimate of total data center usage. For example, if the data center supplies 1 MW of power to an IT load and the IT load consists of 100 racks, the maximum power level can be estimated to be around 10 kW for most racks. This is easier to estimate and implement than calculating the maximum for each individual rack.


With the internal racking considerations finalized, decisions can now be made about the overall capacity allocation of the row. The voltage used (i.e. 240V, 400V, etc.) should be specified. In addition, decisions must be made on whether to supply single or three-phase power to the rack.
The local power distribution diagram (voltage and phase) and estimated power requirements will determine the input power cord or whip amperage required for the IT rack. Typically, rack PDUs will be available with 10amp, 16amp, or 32amp ether input ratings. If more power is required in one rack, an additional PDU should be installed on separate circuits.

10amp and 16amp PDU inputs are usually available with C14 or C20 plug type. Typically in data center environments, a 16amp PDU will be available with the EC309 plug type, commonly known as a commando connector. For higher loads requiring a 32amp input, rack PDUs are almost always supplied with a 32amp commando connector.


Rack PDUs can also monitor power and provide visibility into instantaneous power consumption in addition to overall power consumption trends over an extended period of time. There are three levels of power status visibility: Basic PDU, MeteredPDU , Metered by Outlet PDU & Switch PDU.

  • Basic PDU

The metered metering PDU can locally monitor load levels and avoid potential overloads with built-in digital current meters while providing reliable, rack-mount, multi-socket power distribution, single or three phase, from any UPS, generator or input power protected power source.

  • Metered PDU

The metered metering PDU can locally monitor load levels and avoid potential overloads with built-in digital current meters while providing reliable, rack-mount, multi-socket power distribution, single or three phase, from any UPS, generator or input power protected power source.

  • Meterred by outlet PDU

While similar to the Metered PDU, Meterred by outlet PDU is a bit more advanced with the ability to remotely monitor voltage, frequency, and single or triple loads. phase in real time through the built-in network connection. Output current consumption is displayed locally via a visual meter to warn of potential overload before critical input sources become overloaded.

Connecting additional equipment to the PDU could overload it or the supply circuitry, causing the breaker to trip or the device to fail. Both measured and monitored PDUs display real-time load levels, allowing additional equipment to be securely connected. The main input plugs into the On-Line UPS system. The secondary input plugs into a wall outlet. If the UPS system is used offline for maintenance, repair or replacement, the PDU will keep the load powered by automatically switching from the main input to the auxiliary input due to its ATS function. When the UPS system is restored, the PDU switches back to the main input.

  • Switched PDU

What if you want the ability to remotely monitor, connect, or disconnect your data center loads? No problem! A Switched PDU provides all of these capabilities. A Switched PDU can locally monitor load levels and avoid potential overloads with built-in digital current meters, as well as remotely control individual outlets to restart locked equipment to avoid costly service calls, custom power on/off sequences, and offloading unnecessary loads during power outages to extend battery backup runtimes for critical equipment. Unused PDU sockets can be locked electronically to prevent unauthorized hardware connection. Built-in local digital display and remote web/network interface reports detailed voltage, amperage and kilowatt output values ​​per breaker band/phase with additional reporting options for percent power unbalance, IP address, and optional sensor-based temperature and humidity data. Network interface PDUs connect to the Ethernet jack. Remote users can enable or disable each PDU store via SNMP, Web or telnet.


Typically, each IT device has a backup power source to provide power in case the other fails. For data center applications, these power supplies are typically connected to separate redundant rack PDUs that, in turn, are powered from separate sources or circuits. This prevents the entire load from dropping in the event of a fault along an electrical path.

Rack PDUs mount to the back of server cabinets and provide convenient outlets for both IT equipment and the user to configure it. The two main mounting directions are:

Horizontal 482.6mm (19in) rack mountable PDUs are primarily used with open frame racks and with audio/video equipment.

Vertical 0U or ZezoU PDUs distribute vertical mounting of sockets closer to the equipment they power. This style is the preferred orientation in data centers because they do not take up U rack space and allow shorter power cords and require less cable management. This orientation provides a clearer and more visible electrical path for all wires.
Rack PDU selection should begin with an understanding of the type of equipment to be installed. IT equipment will regulate the type and number of sockets, as well as power consumption requirements. Using power requirement estimates and site voltage information, whips and input wires can be sized appropriately.

Additional consideration is required to prevent overloaded circuits and high temperature applications. Metered rack PDUs can alert administrators before circuits become overloaded and reduce the risk of downtime. They provide past power usage data that can be used to make better decisions than just instant reads.

For most cases, standardizing on one or two rack PDUs suffices for practically any cabinet in the data center.

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