When purchasing UPS for your business or organization, many factors should be taken into consideration, among which the choice of power supply between single phase UPS and three phase UPS is the foremost one. Though both of the UPS offer consistent backup power for dealing with unexpected situations, they have different roles. Here is a brief introduction of single phase vs three phase for those who are unfamiliar with their difference.

What is the phase in Electrical Terms?

If you are new to the world of electrical power, you may know little about the term phase. Phase, at its most basic, is the distribution of electrical power, which shows the alternating current (AC) power supply varies with respect to the time period. There are one phase, two phase and three phase power supply types.

Single phase AC power

Single phase is commonly called “residential voltage” because it is widely available in homes. For example, the microwave oven, the coffee machine, your PC in your household can be single phase devices. In different regions there is a similarity for single phase connections: It requires two wires (one voltage wire and one neutral wire) for completing the circuit. The figure below shows the current flow in single phase AC power.

Single phase AC power

Two phase is basically the same thing as single phase, which consists of AC with two wires. It is also called the split phase. The power is supplied by either one of the two 120V power circuits in loads using low power circuits such as light, television, etc. Nowadays, three phase has replaced the original two phase power systems for power transmission and utilization.

Three phase AC power

Three phase power contains either 3 live wires or 4 wires (3 phase wires and a neutral one), providing three alternating currents, separated in phase angle. The total loads are shared by the three wires. Most commercial buildings in North America use three-phase, four-wire power setups.

Three phase AC power

How to choose the UPS?

UPS units come in two different formats: single phase online UPS and three phase ups. How to select Your industrial uninterruptible power supply UPS. The common phase configurations for UPS are shown in the following chart:

InputOutputNomenclatureUS Mains Voltage
1 Phase1 Phase1/1120/120Vac, 60Hz
3 Phase1 Phase3/1220/120Vac, 60Hz
3 Phase3 Phase3/3220/208Vac, 60Hz

What is single phase UPS?

Single phase UPS have a single input and output source to the electrical equipment. With just one sinewave voltage, it only requires two wires to complete the circuit, one conductor and one neutral.

Single phase uninterruptible power supplies typically cover requirements up to 30 kVA and are used for smaller installations such as rack-mounted servers, telecoms or computer systems, and network switches, along with any device that runs directly from a standard three-pin plug.

Prostar Single Phase Online UPS Diagram

What is a three phase UPS?

Three phase UPS use three separate conductors providing three sinewaves, each out of phase and spaced 120° apart from each other, to provide continuous power to the load. This means a three-phase system needs a minimum of four wires (three conductors plus one neutral), which enables it to support a single phase or three-phase output.

3 phase online UPS are the standard choice for larger installations with critical loads such as data centres, industrial applications, and medical environments, as well as protecting equipment with motors such as lifts, pumps, and fans.

Three Phase UPS

What’s the difference?

The key difference are the following points:

  • Conductor: The number of the conductor in single phase and three phase system is different. single phase contains one conductor while 3 phase supply power through three conductors.
  • Sine wave: 1P provides a single sine wave, while 3P provides three sine waves, each out of phase and spaced 120° apart from each other.
  • Voltage: Single phase voltage is 120V in North America, while the phase to phase voltage for a three phase system is 220V, and the phase-to-neutral voltage is 120V.
  • Maintenance: The plug and play characteristic of single phase makes it easier than three phase counterpart to install and set up without the need for outside installation.
  • Efficiency: For low power requirements, single phase is more efficient that 3 phase. But when the demand for power is higher, 3 phase online UPS shows more efficiency to carry a greater load in a safer manner.
  • Cost: The equipment in 3 phase online UPS system will have longer life expectancies and the transmission lines for 3 phase power do not need the heavy gauge copper wires as single phase UPS, thus, in the long run, three phase UPS will save more money.
  • Application: Single Phase UPS units are available in those applications with lower kVA requirements, generally less than 30kVA, such as homes, small business and satellite offices. 3 phase UPS units are commonly used in large installations, such as data centers, and large industrial power applications with higher power requirements.


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