An external maintenance bypass switch is used to isolate the Uninterruptible Power Supply during routine maintenance such as unit replacement without any disruption to the load. Because it is a manual switching method to transfer the load between UPS output and the mains power supply, the switch is also known as a manual bypass switch. External maintenance bypass switches tend to be mechanical in the form of a wraparound or rotary switch or set of circuit breakers.

Unlike External maintenance bypass switch, static bypass switch in online UPS is a non-contact switch, is to use two SCR (SCR) reverse parallel composition of a communication switch, its closed and disconnected from the logic controller control. It will automatically and instantaneously transfers the load to the mains electricity supply in the event of overload, UPS failure, load current changes and etc.