For reasons of economy, small pluggable UPSs, 0.7kVA – 3Kva, do not incorporate a manual service by-pass switch, like their higher power brothers. This manual by pass switch, allows the service engineers to switch the load (your computers or other equipment) directly to the electricity supply, temporarily. This process takes place without affecting or switching off your load. It also allows engineers to deactivate the UPS electronics, for safe service, battery replacement or repair of the UPS. After the service, the manual by-pass switch allows the reconnection of your load to the UPS, again without interruption of power, which once more provides protection to your equipment.
A manual service by-pass switch is recommended in applications using pluggable UPSs, which simply cannot afford to switch off their load, even for UPS service. This is the reason of large UPSs always incorporate such a switch as standard.