Why Fuses Instead of Breakers For UPS Distribution Panels?
The goal of any well designed UPS system is to maintain power to the load at all times. However, since the output of the UPS is generally fed through a distribution panelboard to the load, there may be times when an overload or fault occurs on one or more branch circuits that has the potential for dropping the load(s) on that branch. This condition needs to be limited to only that branch, and not affect any other loads, or upstream electrical equipment! Therefore, it is imperative that the fault condition be cleared as quickly as possible. Most molded case breakers, used as branch breakers in panelboards, take 2-3 cycles (50 milliseconds) before they will open under short circuit or fault conditions. Fast-acting fuses, such as the Gould Shawmut A25X , however, have much faster clearing characteristics, typically 1/4 cycle (4 milliseconds). Many UPS systems (inverters) will not provide enough fault clearing current for the 2-3 cycles required to clear those types of breakers. Fuse clear
