The Difference in Single-Phase and 3-Phase Power

If you’re running a commercial building or industrial facility, 3-phase power offers more power for the equivalent amount of current than single-phase power. Unless you have some basic electrical training, you're probably wondering what 3-phase power means, and how it differs from residential single-phase power?

What is 3-Phase Power?

3-phase power is a method of generating and transmitting electric current, and is one of the most common means of transferring power across electrical grids. North American grids usually convert 3-phase to single phase before delivering power to residential buildings. Commercial buildings tend to be wired for 3-phase power as 3-phase power is well suited to carry heavy loads.

Single-Phase vs. 3-Phase Power

Single-phase power is the most common type of household circuit, used to power lights, televisions, and other small appliances. The US uses 120 volts for standard single phase power, while some nations prefer 240 volts.

No matter the voltage, all single-phase circuits are two-wire alternating current (AC) circuits, composed of one power wire and a neutral wire. Power flows between the power wire to the neutral wire. This produces rises and falls in voltage. Power is not delivered at a constant rate, which is fine for most households, but could cause problems for industrial facilities.

3-phase power is more like a three-piston engine. A 3-phase circuit uses three AC power lines, each running 120 degrees out of phase with the other two. This ensures power never drops to zero and makes it possible for the circuit to carry more load.

3-Phase Power Calculation

Making a 3-phase power calculation is easy. Power from a 3-phase circuit equals voltage multiplied by current multiplied by 1.732 (the square root for 3). As a result, a 3-phase circuit provides 1.732 more power than single phase power, which reduces energy costs for commercial buildings.

Most US commercial buildings have 3-phase 4 wire 208Y/120V power. Industrial facilities tend to need the more robust 3-phase 4 wire 480T/277V system, which delivers 2.3 times more power than the 208V 3-phase.

While the difference in single-phase and 3-phase power is marked, the same formula is used to calculate the power produced by each system. Power is the sum of Voltage (think of it as the
pressure the circuit produces) multiplied by Current and amperes (the “speed” which the voltage flows).

How to Convert 3-Phase to Single Phase

Commercial facilities may need to convert 3-phase to single phase power in order to wire power to equipment that requires single-phase power. Employees with electrical systems training can install a phase converter between the machine and the power supply to convert 3-phase to single phase power. Employees with only basic electrical knowledge should not attempt the installation.