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An Uninterruptible Power Supply, also Uninterruptible Power Source or by the acronym UPS, is an electrical apparatus that provides emergency power to a load when there is a power outage. Unlike an auxiliary power system, such as a generator, the UPS will provide instant power during a failure for a seamless failover. The UPS supplies power from batteries and therefore is limited in duration, allowing time for equipment to be properly shut down reducing load, or time for an auxiliary power system to kick in. The primary role of any UPS is to provide short-term power when the input power source fails. However, most UPS units are also capable in varying degrees of correcting common utility power problems. The UPS can serve as a form of surge protection, depending on the unit design. Other correcting capabilities of some UPS units include protection against brown out variations, harmonics and other forms of line noise, and frequency variances.=== For the Impatient: How Much Protection You Need ====== For the Impatient: How Much Protection You Need ==='''On-line''' UPS systems employing double conversion topology, not delta conversion or ferroressonant, are the only true on-line types. The on-line UPS is constantly engaged, converting all incoming power to DC current which passes though the battery circuit (DC bus) and is converted back to AC again. Equipment connected to the on-line UPS is electrically isolated from utility power and receives continued highly regulated power. This design prevents any output power disturbance or gap when there is utility power loss or an anomaly in the incoming power since the battery circuit is always engaged. An on- line UPS can accept as low as 50% normal incoming voltage without drawing battery power, greatly increasing battery life. Liebert single phase on-line UPS systems have hot swappable batteries that typically last (5) years.[[File:ups-tripplite.jpg]][[File:ups-tripplite.jpg]]