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ITGlossary · Electrical units
Three-phase Power
A supply with three AC phases shifted by 120° (400 V between phases), used for large loads, motors and UPS systems from about 10 kVA.
Technical level:Intermediate
In three-phase power, electricity is distributed over three phases shifted by 120° from each other, usually with a neutral conductor. In Greece the voltage between phases is 400 V and between phase and neutral 230 V. This carries more power with smaller cable cross-sections and runs motors, lifts and large air-conditioning units smoothly.
UPS units come in 3/1 (three-phase input, single-phase output) and 3/3 (three-phase input and output) configurations. Three-phase units are typically used from about 10 kVA upwards, in data centres, industry and hospitals.
A common problem is imbalance: when single-phase loads are not spread evenly across the three phases, one phase becomes overloaded while the others are underused.
Related terms
- kVA (kilovolt-ampere)A unit of apparent power equal to 1,000 VA, used to rate UPS systems; real power in kW equals kVA × power factor.
- Single-phase PowerAn electrical system with one alternating current (AC) voltage phase, commonly used in homes and offices.
- 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.
- Load SheddingA method used to prioritize power delivery by disconnecting non-critical loads during outages.
- Noise (Electrical)Unwanted high-frequency disturbances on the supply voltage, e.g. from motors or power supplies, which UPS systems and line conditioners filter out.
- Hardwired (Terminal Block) ConnectionPermanent connection of the UPS input or output by an electrician, with cables screwed into a terminal block instead of plugs and sockets, usually on higher-power UPS units.