Most people give little thought to the electricity that comes from a wall socket. However, electrical power is a key consideration for data center managers. Ever-increasing power requirements have tested the limits of many data center facilities.
Office buildings in the U.S. generally have single-phase power, while world-class data centers have three-phase power. Three-phase power offers several benefits for power-hungry IT equipment, but it requires a different type of power distribution unit (PDU) than single-phase power.
3-Phase Power Compared to Single-Phase Power
Most people are familiar with alternating current, or AC. The typical power plant will generate and provide a voltage from cyclical motion, which results in a sine wave voltage curve. By using a generator with three output circuits at 120 degrees from each other (since 360 degrees makes a complete circle), the maximum stability can be obtained for the mechanical design of the generator. It can be noted that the voltage, and thus the current and power, alternate positive to negative many times per second.
It is important to note that the standard voltage available to residential and industrial facilities varies worldwide.
What Is Single-Phase Power?
Single-phase power describes the point in the distribution of power where one sine wave is split off from the others. Single-phase power is used in homes and offices because the equipment power requirements are typically low. You will see around 120 volts on the typical outlet in North America and about 230 volts in Europe, with some other variations worldwide.
A common form of single-phase in the U.S. actually uses two of the three phases to create a single sine wave at 208 volts. Regardless, all single-phase circuits will have three wires – the “hot,” the “return,” and the “earth ground.”
The power available from a single-phase circuit is simply the voltage times the maximum current of the outlet connection. Beyond that current, the circuit breaker or fuse protecting the circuit will trip. An example might be a 10-amp socket at 120 volts to provide up to 1,200 volt-amps. This is often simplified incorrectly as watts, but we can leave that to another discussion.
What is 3-Phase Power?
With three-phase power, three circuits are available as single-phase. Note that there is industrial equipment that will utilize the three-phase power more directly, but for this discussion, the end usage is still single-phase. The three-phase circuit will have four or five wires depending upon the needs – three “hot,” a neutral “return” (not used in all systems), and “earth ground.”
This is where things can get a bit confusing. When we talk about the common voltages of 120 in North America and 230 in Europe, these circuits have a neutral wire for return. Taking these to three-phase means you would have five wires instead of three and get three times the amount of power. Each of the three circuits consists of a unique “hot,” a shared “return” on neutral, and a shared “earth ground.”
The 208 volts mentioned above are the complication. It uses the same basic structure as the 120-volt North American three-phase circuit but is wired such that the “hot” wires are shared. That is, each of the three circuits is a primary “hot,” a secondary “return hot,” and the shared “earth ground” with no “neutral” wire. This means that each “hot” line is on two distinct phases as viewed by the load attached.
Using the same math as before, 10 amps times 208 volts would lead to 2,080 volt-amps. But you can’t just multiply that by three to get the total available power. The wiring can’t magically provide more power just by connecting to it differently. The hint is that each of the ”hot” lines carries the voltage at different levels for each of the two circuit loads. The two loads are out of phase with each other by the 120 degrees of the originating power system. This results in a multiplier of √3 x 2080, equal to 3 x 1200.
3-Phase PDU vs. Single Phase PDU
You need different types of PDUs for single-phase and three-phase power. A three-phase PDU tends to be more expensive than a single-phase PDU, and the cord is thicker and heavier because of the additional wires. But you need fewer three-phase PDUs to power the rack or cabinet. That means fewer pieces of hardware to buy and fewer cords to manage. The thickness of the three-phase PDU cord is less than that of multiple cables required to deliver the same amount of power, simplifying installation and saving valuable space in the rack or cabinet.
Some three-phase PDUs can provide outlets for both 120V and 208V devices. They are also more resilient. A three-phase PDU has more circuit breakers than a single-phase, so you lose fewer outlets if a breaker is tripped. For more information on how to choose the right PDU for your application, check out our PDU buying guide.
High-Quality PDUs from Enconnex
Enconnex offers single-phase and three-phase PDUs to meet a wide range of power requirements. From basic to input metered, outlet metered, or switched, our PDUs are manufactured using premium, high-temperature, branch-rated hydraulic-magnetic circuit breakers. Labeled outlets and circuit breakers allow easy identification of circuit configuration for reduced connectivity errors.
Our universal PDUs feature a seven-pin input connector that supports interchangeable input power cables. You can standardize on our universal PDU across your environment and adapt it to different power sources in various facilities.
Contact one of our power specialists to discuss your requirements.
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