Why Choosing the Right Rack PDU Makes a Difference for Your Data

The right rack PDU selection hinges on key metrics like center size and built-in features. Here’s what you need to know before starting the process.

Key takeaways:

• The first step in selecting a PDU should be calculating your base power requirements.
• You’ll need to measure power input and identify output type.
• Choose the built-in PDU features that suit your needs.
• Select horizontal, vertical, or mixed mounting as your racks demand.

The world of commercial electrics is full of abbreviations. One of the most important for the IT sector is the power distribution unit (PDU). These units are essential because they transport unconditioned power from a utility source, generator, or uninterrupted power supply (UPS) into the IT equipment.

Not every unit is created equal, though. This guide will spotlight the parameters to explore before choosing a rack PDU for your data center, plus provide tips to help business owners determine the optimal set up to suit their power requirements.

Know your basic power needs

Determining your basic power needs requires just a simple calculation. Every device should have its wattage or volts and amps requirements clearly printed on its exterior. You may also find this data in the user’s manual. Tally these numbers from all the devices you intend to connect and you’ve got your total data center power consumption.

This sum is important because it helps in selecting your input power mode – a UPS, generator, or other item – which should have a higher consumption figure than your tally. The excess allows for future data center growth and powers additional devices such as lights, fans, and humidity or temperature sensors.

Identifying the input power and output types

Data centers reside in different kinds of buildings that provide either single- or three-phase input power. Single-phase delivers 60 cycles per second of alternating positive and negative voltage at 120V or 208V. Three-phase provides 208V or 400V and lacks the zero-voltage instant single-phase does on every cycle shift. This is because two waves are always at positive/negative points when the third is zeroed out. 

Phase grading is thus key because it decides the input power cord type. Racked IT equipment uses different outputs depending on the required current carrying capacity. C-19 and C-13 are the most typical for larger and smaller racks, respectively, but combinations on the same rack are also common.

Your plug type matters when choosing a rack PDU, so it’s important to know that the National Electrical Manufacturer’s Association (NEMA) has various kinds in circulation. The type determines the connector’s construction features. Identifying yours allows you to choose the rack PDU with the right plug construction, sufficient current load, and more power outlets than you need. Excess outlets let you scale up without delay and have fallbacks if one or more fail. 

Keep in mind that racks often need fans nearby to aid with cooling, so you’ll want to factor this into your outlet count if using a basic PDU.

Selecting PDU features

Rack PDUs range from basic to advanced. Some provide alerts on connected devices or allow for remote monitoring, which can be instrumental in rebooting from offsite or preventing unauthorized access. Understanding the varying performance features assists you in choosing the right one.

• Basic PDUs
  These share their power source with multiple devices and deliver AC power without any built-in data displays. They are reliable, despite their basic build, because they lack features like surge suppression which can interrupt power flow. The downside is that the missing data display leaves users guessing as to power levels and potential issues.
• Switched PDUs
  These are ideal for offices with no onsite IT staff and come in switched auto transfer or metered auto transfer switches (both abbreviated as ATS), metered-by-outlet, or plain switched types. Switched PDUs are good for continuity, as they can be programmed to terminate non-critical loads during power failure to prioritize critical systems. Standard switched PDUs can power a network and be locally or remotely controlled while displaying voltage and load data. These displays help isolate power issues and give users a heads up when approaching capacity.Metered-by-outlet PDUs have the abilities of standard switched units with the added functions of load shedding and remote switching. Metered ATS can also be locally or remotely managed, and display power data such as kilowatt consumption, amps, and input and output voltage. Switched auto transfer PDUs display the same data as metered models, can be remotely managed, and can shield racks against redundancy. 
• Monitored and Metered PDUs
  Monitored models have a digital display showing instantaneous information allowing IT and electrical teams to check power levels. Remote monitoring is also an option with these network-grade power distributors. Metered models meanwhile deliver the same amount of power in amps, and can help with load optimization and overload prevention by providing advance alerts that racks are approaching predetermined limits. This assists in avoiding tripped breakers.
• Maintenance Bypass PDUs
  These allow quick and easy switching between a UPS over to a utility power supply. The option is ideal for continued operations if you’re doing any kind of installation or maintenance work on your rack PDU setup.

Rack PDUs are also available in a number of colors which help minimize human error and simplify the identification of power chains, voltages, and feeds for IT technicians and electrical teams.

Vertical vs. horizontal PDUs

Rack PDUs come in vertical and horizontal mounting configurations with either choice dictated by available space. Your PDU’s angle matters because choosing the wrong one could result in stress on plugs and cables leading to accidental unplugging or excessive cable bend.

Verticals connect to the upright rails of a rack enclosure and are known as zero-unit (0U) strips. This is because they won’t take up mounting spaces with overhanging cables. Horizontal strips typically take up 1U to 2U of space, meaning the number of outlets free for use is limited by rack length. Horizontals can be a better fit if you’re using an in-rack UPS.

Get the right rack PDU with UES

At Universal Electrical Services, data centers are one of our many specialties. Our experts have years of experience in building, renovating, and relocating data centers, and can provide advice or quickly add one or more new rack PDUs to your existing setup with minimum inconvenience. That means you maintain mission critical power while getting the upgrades you need. 

Visit our contact page to speak with one of our commercial electrical experts.