Single Phase vs. Three Phase Power: What You Need to Know?

Mike Allen
November 06, 2014

"Many of the residences in the North American and European regions use single-phase alternating current electric power supply, which is typically used for powering up lights and household appliances. However, a single-phase system may not be the best choice when it comes to industrial or business usage as it involves heavy load and power requirements. As today's data centers are growing power hungry with a need to provide more computing and storage capability to keep up with the explosion in demand, power supply has become a major consideration. Traditional single-phase systems can no longer keep up with the power requirements for these data centers without going through a rewiring process as the number of units that can be mounted in a rack has gone up way high because of miniaturization. Fortunately, three phase power distribution systems can come to the rescue with their superior power carrying capability at a reduced cost. Here are some of the key differences between single phase and three phase systems that you need to know.

How do single and three phase systems work?

Single-phase systems use alternating current electric power in which the voltage and current flow changes in magnitude and direction in a cyclical fashion, typically 60 times per second. In the U.S., single-phase voltage is 120 Volts, while several countries use 230 Volts as the standard. A variation of single phase, called split phase, is also in effect in the U.S. where two wires carry 120 Volts each with a common neutral, providing the option to hook up high power loads to the 240 Volts power circuit and low power loads to 120 Volts power circuit.

In three-phase systems, the power circuit combines three alternating currents that vary in phase by 120 degrees. As a result, the power would never drop to zero, making it possible to carry more load. In a typical 120 Volts power arrangement, this is equivalent to three 120 Volts single-phase power circuits and one 208 Volt power circuit.

What are the benefits of three-phase systems over single-phase?

The cost to install and maintain three-phase systems is substantially lower than that of single-phase systems. Three-phase systems use substantially less conductor material than that of single-phase systems - about 25 percent less for the same amount of power delivered. For the same amount of time, three-phase power lines can carry more power than that of single-phase power lines at a reduced cost. In addition to reduction in copper, a three-phase system requires fewer circuit breaker pole positions for 208 Volt loads. The power delivered is almost constant in three-phase power circuits, making them ideal candidates for transmission lines, power grids, and data centers.

How can three-phase power systems help datacenter power requirements?

Today, one can easily fit 60 or more blade servers in a rack - much more than few handful of servers one could fit in a few years back. The increased count of servers may not be handled well by the single-phase power systems because of the increase in the amperages for plugs and sockets to connect to them. Additionally, these single-phase lines have to be pulled from the existing power lines, presenting a challenge to keep the phases in balance. By directly delivering three-phase supply to the server cabinets, the cost of cabling is greatly reduced, simplifying the electrician's job. Installing three-phase systems in datacenters helps to consolidate the power distribution in one place, helping to cut down the costs associated with installing multiple distribution units. Multiple racks can be powered with fewer three-phase power distribution units, reducing the power utilization and helping to lower the costs. Reduced need for cooling also helps to further cut down the energy requirement, optimizing the power utilization.

A typical North American system contains three types of wires for single-phase power supply - hot, neutral, and ground wires. A three-phase power system, on the other hand, contains three hot wires, a neutral, and an optional ground. There are different ways to draw power from three-phase system. In delta configuration, power is drawn by combining any two of the phases to form a circuit, while wye configuration includes a phase and a neutral. The first combination results in 208 Volts while the second one results in 120 Volts. This kind of setup provides maximum flexibility in terms of voltage and power, helping to balance power across all the equipments. Three-phase systems are also safer to work, and require a lower labor and equipment to handle.

Selection of an appropriate power-distribution system is very crucial for the success of any business. While single-phase power supply may not be an issue with home users, companies need to rethink their strategy on the datacenter power requirements by considering three-phase power supply. A properly designed clean power system can ensure a robust power-distribution network that can power up multiple equipments with different power requirements, and return a clean power back to the power grid where possible."



    Mike Allen

    "Many of the residences in the North American and European regions use single-phase alternating current electric power supply, which is typically used for powering up lights and household appliances. However, a single-phase system may not be the best choice when it comes to industrial or business usage as it involves ...