The UPS are critical to ensuring a consistent flow of electricity in the event of a public utility power outage.

The size and capabilities of the UPS system should be guided by a few key criteria. First, the UPS should be sized to power all computer equipment, HVAC systems, and other electrical devices (such as emergency lights and security devices) for no less than 15 to 20 minutes following a power outage. Second, the UPS should be sized to handle "peak" loads or fault overloads. This is related to the first increase in power demand when the device is turned on. As a general guideline, size the UPS to meet 150 percent of operating demand. Third, the UPS should be active all the time to filter and condition the electricity.