10 Factors to consider when Choosing a Rack PDU

In it’s simplicity, rack power distribution units (PDUs) are designed to provide electrical protection and distribute power to networking equipment within racks/cabinets. As the needs and requirements of data centers altar, so do options for rack PDU performance.

There are several questions to consider before selecting rack PDUs that will work well for your data center application. This list below will aid you in the right direction, ensuring that the PDUs you choose will fit the design of your data center today and in the future.

1. Type of Mount

Depending on where you want to station it, a rack PDU can be mounted horizontally or vertically. Installed horizontally inside the rack (taking up RU space) is one option; another option is to vertically mount a PDU on the back or side of the enclosure (not taking up any RU space). You will often see one vertically mounted PDU on the left side and one on the right side of a data center cabinet (although rack PDUs can be mounted on either side, based on preferences).

PDUs can be mounted so that power cords exit either at the bottom or top of the enclosure. (If your data center is on a slab, for example, the power cord needs to exit at the top of the enclosure because there is no raised floor for it to pass through.)

2. Amperage

Your power rating – the amount of sustained power draw a PDU can handle – determines the amperage level you’ll need. Why is this important? Because, for example, a PDU with a 30A fuse will blow if a 30A circuit experiences more than 30A of power for an extended period of time.

Per the National Electrical Code, 30A PDUs or higher are required to be equipped with a 20A breaker to prevent injury in the event of a short circuit.

3. Voltage

In addition to different amperages, there are different input voltage options for rack PDUs as well; 208/240V is the most common voltage output to computing gear, with a new trend moving toward 400V input. Confirm your infrastructure voltage, and you’ll know what type of voltage you need in your PDU.

4. Single- or 3-Phase Power

What type of input power do you have access to: single-phase power or 3-phase power? The type of power distribution in your data center will determine whether you need a single- or 3-phase PDU.

The difference involves where in the distribution system the phase is broken down. When it’s broken down at the distribution panel, power to the rack will be single-phase service (requiring single-phase rack PDUs). When all three phases are brought to each rack, then a 3-phase PDU is needed. In most data centers, the input power is 3-phase service.

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