An uninterruptible power supply, also uninterruptible power source,UPS or battery backup, is an electrical apparatus that provides emergency power to a load when the input power source, typically mains power, fails.

A UPS is typically used to protect computers, data centers,telecommunication equipment or other electrical equipment where an unexpected power disruption could cause injuries, fatalities, serious business disruption or data loss. UPS units range in size from units designed to protect a single computer without a video monitor (around 200VA rating) to large units powering entire data centers or buildings.

A PABX system relies on power, loss in power results in loss in telephone lines, by having a UPS you will be able to stay online while your power source is rectified.