An uninterruptible power supply (UPS) system 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 hardware such as 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 to large units powering entire data centers or buildings.