Bypass AC under voltage
 

Our two rackmount UPS occasionally emits an audible alarm which is caused by a "Bypass AC under voltage" event. What is the cause of the event, and how do we address this issue?

While possible you have a hardware problem, normally this event indicates out of spec commercial input AC power. You should first have the AC power checked. The UPS continuously compensates for (effetively smooths out) slight deviations in commercial input power but can only do so much before it either has to shut down or either goes into or must be manually put into battery backup mode.