When a customer has several independent critical loads, they have the choice of putting all the loads on the same UPS or placing the loads on separate UPS units. When all the loads are on the same UPS output, a significant overload on anyone of the legs might be large enough to put the unit into bypass. Once this occurs, the backup protection is temporarily lost for all loads until the overload is removed. If this is not an acceptable solution because of the highly critical protection requirements, the normal alternative is to provide separate UPS units for each load. This will insure that a problem in one critical load will not affect any other critical protection requirements, but this is an expensive approach.
A less costly solution to this problem is to use multiple static switches on the UPS' output. One static switch is configured for each load. If an over current in that load occurs, it will be switched without interruption to bypass without affecting any other load. The rest of the loads will continue to be powered by the inverter. When the overload abates, the individual static switch will return that load to the inverter. The advantage here is the significant savings possible compared to one UPS unit for each load.