A bypass automatically and instantaneously transfers the load to the mains electricity supply when there’s an internal fault or failure with your UPS system. This allows general servicing to continue without causing disruption to the load. In effect, running on a bypass circumvents the UPS (i.e. the rectifier, batteries and inverter) and ensures power continuity while the UPS is fixed or swapped out.
Internal static bypass switches should not be confused with an external maintenance bypass switch, which is an option that enables the UPS to be powered down manually for maintenance to be carried out while the critical load is powered directly from the mains. External maintenance bypass switches tend to be mechanical in the form of a wraparound or rotary switch or set of circuit breakers.