The Difference in Single-Phase and 3-Phase Power

The difference in single-phase and 3 phase power is difficult to grasp if you’re not an electrician. 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. Here’s why.

Calculating Power

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).

Single-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 other 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.

Dual / Split Phase Power

Occupying a middle ground in the difference in single-phase and 3-phase power is the dual or split-phase power circuit. Instead of a single power wire, a dual-phase power circuit has two 120-volt AC power lines running 180 degrees out of phase with each other to produce continuous power, allowing the circuit to handle higher power loads. A dual-phase power circuit is a little like a set of bicycle pedals: when one “foot” (a power wire) exerts force (voltage), the other picks up the slack.

If dual-phase power is a bicycle, 3-phase is more like a three-pistoned 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.

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 in turn reduces energy costs.

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.

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