Equipment that ensures continuous electrical power when the main source of electrical power is interrupted to a building, space, system or piece of equipment. The UPS is installed to detect the interruption and provide replacement power before the interruption cuts off the flow of power to the systems protected. The UPS may be designed to provide power to an entire set of systems for a brief period of time until another source of back up power (for example a diesel generator) begins to function. It may also be designed to provide power for a longer period to specific systems, such as Life Safety Systems, servers or data storage centers. Usually the UPS relies upon batteries to supply power.