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ITGlossary · Electrical units
Phase
Each conductor carrying alternating voltage in an AC system; supplies are single-phase or three-phase depending on their number.
Technical level:Intermediate
In alternating current the voltage varies as a sine wave, at 50 Hz in Europe. A single-phase supply has one phase conductor and a neutral at 230 V and is the usual arrangement in homes. A three-phase supply has three phases offset by 120° from each other, with 400 V between phases and 230 V from each phase to neutral.
Three-phase power is used in commercial premises, industry and larger homes because it carries more power and can drive three-phase motors. UPS systems come in 1/1, 3/1 and 3/3 (input/output) configurations, depending on the supply and the loads.
A common mistake in three-phase installations is an uneven distribution of loads across the phases, which overloads one phase and puts extra stress on the neutral.
Related articles
Related terms
- Single-phase PowerAn electrical system with one alternating current (AC) voltage phase, commonly used in homes and offices.
- Three-phase PowerA supply with three AC phases shifted by 120° (400 V between phases), used for large loads, motors and UPS systems from about 10 kVA.
- Charging Power (kW)How much energy flows into the battery per hour, which in AC charging depends on voltage, current and the number of phases.
- DC VoltageRefers to the direct current (DC) voltage level, typically that of a UPS battery.
- IEC C13/C14 ConnectorsStandardised pair of connectors rated up to 10 A under IEC 60320, found on UPS outputs and on the power supplies of computers, servers and monitors.
- IEC C19/C20 ConnectorsPair of connectors rated up to 16 A under IEC 60320, used on higher-power UPS units, rack PDUs and servers or switches with high-consumption power supplies.