Discover the difference between single-phase and three-phase power supplies

Three-phase power, the most efficient way to distribute power over long distances, allows for large industrial equipment to operate more efficiently. It’s characterised by three single-phase waves that are offset in their phase angle by 120 degrees, or one-third of the sine wave period as illustrated in figure 1. Three-phase voltage can be measured from each phase to neutral or from one phase to any other. The voltage relation between phase-to-neutral and phase-to-phase is a factor of the square root of three (e.g. 120V versus 208V).

Three-phase power:

• Is common in most large businesses and high-density data centres with higher kVA and rack applications
• Is used for applications requiring greater than 1000 watts
• Is used to balance the loads on the utility power of the building
• Is safer and more cost effective to run
• Is delivered in a steady stream at a constant rate

Single-phase power is distributed through common household outlets to power everyday equipment such as laptops, lighting and televisions. When looking at an oscilloscope image of the voltage coming out of a single-phase outlet as illustrated in figure 2, there’s only a single wave. Single-phase power is obtained by simply using only one phase of a three-phase system. Its root mean square (RMS) voltage is 120V (for North America) and it oscillates between its peaks of ±170V at 60 Hz (or 60 times a second).

Single-phase power:

• Is used in most residential homes and small businesses
• Is used for a wide range of general applications 
• Is the standard for locations where three-phase power is unavailable
• Is the most efficient for units up to 1000 watts
• Is not delivered at a constant rate