Three Phase Uninterruptible Power Supplies (UPS) Information

Three phase UPSThree phase uninterruptible power supplies (UPS) operate in conjunction with existing electrical systems to provide power conditioning, back-up protection, and distribution for electronic equipment loads that use three phase power. A three phase UPS also prevents power disturbances such as outages, sags, surges, spikes, and noise from affecting the performance and life of the electronic device and vital data. Selecting three phase UPS requires an analysis of technology types, product specifications, and features.


There are three basic types of three phase UPS:

  • on-line or double-conversion
  • line-interactive
  • off-line or standby

With on-line units, the load is supplied from a continuously-operating power converter that receives its input from a DC supply. This DC supply consists of a battery and a large battery charger, which are connected in parallel. With line-interactive devices, the inverter works in parallel with conditioned-input AC power to supply power to the load (boosting or bucking), and only handles the full load of power when the AC input power fails. With an off-line unit, the power is usually derived directly from the power line, until power fails. After power failure, a battery-powered inverter turns on to continue supplying power.


Capacity specifications to consider when specifying three phase UPS are the volt-amp rating, watt rating, and input voltage range. Three phase UPS are rated in volt-amperes (VA) or kilo-VA (kVA). Note that the VA rating is not the same as the power drain (in watts) of the equipment. The watt rating is specified only if VA rating is unknown; the watt rating is less than or equal to VA rating. The input voltage range is the precise identification of the electrical system and is critical in the proper selection and application of a three phase UPS.

Performance specifications for three phase UPS include runtime half load, runtime at full load, and switchover time. Runtimes refer to the length of time the three phase UPS will run at half load, full load, and the amount of time for switchover. Note that on-line or double-conversion devices do not have a switchover time.

Output specifications for three phase UPS include output voltage in battery mode, number of backed-up outlets, and outlet options. Outlet options include additional electrical outlets, RJ type connectors, and coaxial cable connectors. Mounting options for three phase UPS include tower type, rack or tray, strip type or plug strip, and mounts on or in device protected. In addition to battery backup systems, rotary or battery-free three phase UPS are available that use the energy stored in a rotating member as backup energy.

Related Information

CR4 Community—Current Output from a 3-Phase UPS

CR4 Community—Three Phase to Single Phase

Image credit:

Bjoertvedt / CC BY-SA 3.0

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