Single vs. 3-Phase Power

What's the Difference?
Many people struggle with the difference between single- and 3-phase power. A 3-phase system is much more efficient for high-capacity installations, but is much more costly to install. This is why 3-phase utility power is typically only available in industrial and commercial areas.

While most electronics operate on single-phase power, it can be more efficient to install a 3-phase system in the data center. 3-phase systems enable the consolidation of power circuits with 3-phase Power Distribution Cabinets that have a much greater distribution capacity. A single 3-phase Power Distribution Cabinet can power multiple racks, rather than having to install multiple single-phase circuits and incurring the labor and cabling costs that go with it.

There is somewhat of a domino effect of efficiency savings with 3-phase. The increase in power efficiency reduces the amount of power distribution equipment (circuit breakers, PDUs, cabling) that must be installed. This then reduces installation and labor costs. By reducing the amount of equipment that physically occupies the data center, the cooling requirement is reduced, therefore saving energy. The list of potential savings goes on. However, a 3-phase system is only efficient if the load is large enough to merit the initial installation costs that come with it. It really depends on the size and specific application.

How 3-Phase Works
A 3-phase circuit combines three alternating currents of the same frequency, each 120 degrees out of phase with each other. This produces three separate "waves" of power, as represented below. The power in a 3-phase power supply never drops to zero, but in single-phase the power falls to zero 3 times per cycle. Thus, in a 3-phase power supply, the power delivered is constant.
Single vs. 3-Phase Power

Single vs 3-Phase power diagram
While actual efficiency depends on the load-to-capacity ratio, the nominal ratio between the efficiencies is 1.5 in favor of 3-phase when comparing single- and 3-phase power.