What is the difference between single-phase and three-phase UPS systems?

Single-phase uninterruptible power supply systems are commonly used to protect smaller IT installations, individual servers and office equipment. Three-phase systems are better suited to larger installations with higher power demands, such as those found in data centres and on industrial sites. Depending on the model, online UPS systems can support single-phase input and output (1/1), three-phase input with single-phase output (3/1), or three-phase input and output (3/3).