What is an uninterruptible power supply (UPS)?

​An uninterruptible power supply or a UPS system is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails.  A UPS system performs three primary functions: conditions the incoming dirty power from the utility company to give you clean, uninterruptible power, provides ride-through power to cover for sags or short-term outages, and enables seamless system shutdown during a complete power outage.

What is the difference between single-phase UPSs vs. three-phase UPSs vs. split-phase UPSs?

Phases of a UPS, such as a single-phase UPS or a three-phase UPS, describe the number of electrical phases that a UPS receives and transmits. Electrical utilities generate three-phase power because that is the most efficient way to transport electricity over long distances.  And for larger power consumers, such as large data centers, industrial manufacturing and hospitals, the power stays as three-phase, requiring a three-phase UPS. For smaller power consumers, including residential or office buildings and most K-12 schools, the power is converted to single-phase power.

​Some applications contain a mix of single-phase and three-phase equipment and require a UPS that can protect both. For those deployments, a split-phase UPS, which can simultaneously provide 120V and 208V output, is often the best option.

​What size UPS do you need?

UPSs are given a power rating in volt-amperes (VA) that range from 300 VA to 5,000 kVA. This rating represents the maximum load that a UPS can support, but it shouldn’t match exactly the power load you have. To allow room for growth, the best practice is to choose a UPS with a VA rating that is 1.2x the total load you need it to support. If your UPS will be supporting motors, variable-speed drives, medical imaging devices or laser printers, add more VA capacity to your requirements to account for the high power inrush that occurs when those devices startup.

​Companies that are anticipating rapid growth should use a higher multiplier than 1.2x. Newer server hardware tends to have higher power requirements than older models, so factoring in additional VA will account for adding more and newer equipment.