Depending on the load distribution, an alternating power supply can be categorized into single-phase and three-phase. The main difference is that single-phase power is used for low electric requirenments, and three-phase power is for heavy loads, usually in industrial settings.

Single-phase systems can be derived from three-phase systems using a transformer or VFD in the US or directly in the EU.

What is single-phase power?

Single-phase power uses a single alternating current (AC), meaning electricity flows through only one conductor. It's the standard for residential and small commercial buildings that require less power.

Single phase operates at a low residential voltage of 120V or 240V. A single-phase supply uses neutral and phase (live, hot) wires.

• It is suitable for powering small appliances, lights, and residential HVAC systems. We use single power in homes and small businesses instead of large commercial and industrial applications, where three-phase power is used.
• While less efficient for large load applications, single-phase power tends to be cheaper in terms of installation and maintenance due to its more straightforward setup.
• Single-phase power can experience more voltage fluctuations and less stability than three-phase systems, especially under heavy load conditions. However, it is stable in its typical residential applications and is excellent for applications up to 5 horsepower.

What is three-phase power?

Three-phase power uses three alternating currents, each out of phase with the other by one-third of a cycle. This allows for more efficient and stable power distribution without power ever dropping to zero. There are three-phase power configurations with and without neutral wires. There is a 120° distance between three phase wires.

In contrast to single-phase, three-phase power can operate at higher voltages, ranging from 208 V to 415 V, or in some cases, several kilovolts, which is common in industrial and large commercial settings.

• Three-phase power is standard in industrial and commercial environments that require large amounts of energy, such as factories, data centers, and large HVAC systems.
• Three-phase is more efficient at transmitting power over long distances and for large machinery. This can lead to lower operational costs despite higher initial setup costs. 
• Three-phase power offers more stable power with fewer voltage sags and surges. It can power large motors and heavy loads more efficiently and smoothly.

Differences to consider

• Single-phase has one AC waveform, while three-phase uses three, each phase 120 degrees out of phase with the others.
• Three-phase power delivers a more stable, continuous power.
• Three-phase systems are more efficient for large industrial applications.
• Single-phase is used for lighter residential loads, while three-phase is used for heavier industrial loads.
• A three-phase power supply requires fewer wires to deliver the same amount of power than a single-phase system. The overall current flowing through each wire is reduced because the power is more evenly distributed and because three-phase motors and systems can operate more efficiently. This reduction allows for smaller conductors to transmit the same amount of energy.
• Three-phase power cannot handle overload, which often damages the equipment.
• Single-phase power applications include domestic supply, residential homes, small offices and shops, and outdoor lighting.
• Three-phase power applications include industrial plants, commercial buildings, motors, data centers, and agricultural systems.

Can three-phase power be used in residential settings?

Yes, it can.

• Consider using three-phase power load in large houses with multiple HVAC units, pools, spas, large water heaters, etc.
• Many European countries standardly provide three-phase residential electrical supplies because of the growing number of everyday appliances. These include Germany, France, and Norway.
• To test whether you have a single or a three-phase supply, inspect the fuse. Generally, a single-phase supply is indicated by the presence of one fuse, while a three-phase supply will usually feature three 100-amp fuses.