In addition to the internal redundancy that multiple power modules provide, Tripp Lite Modular 3-Phase UPS Systems can provide external redundancy as well. External redundancy is referred to as "1+1" instead of "N+1". Remember, "1+1" refers to deploying an entire identical system as a backup. The two Modular E3 Series 3-Phase UPS Systems that are connected to the same load must be identical: same model number, voltage, and kVA rating. The maximum number of UPSs that can be connected is 2 (remember, it's "1+1", not "1+1+1+ . . ."). IMPORTANT NOTE! GUARD AGAINST UPS SYSTEM OVERLOAD! If the load exceeds the maximum capacity of one of the UPS systems, and one UPS is removed for maintenance, the remaining UPS will be overloaded and will shut down. Using the 80 kVA UPS illustration shown in the accompanying slide: if the load was 100 kVA (instead of 80 kVA) and one UPS was removed, the remaining 80 kVA UPS would be unable to support 100 kVA. As most people may have noticed in the accompanying slide, the two UPS systems share the load in normal conditions. During maintenance, the entire load is automatically shifted to one UPS system. No user action is required to shift support of the load to the redundant UPS system. When connected together to support a single load (often referred to as a "parallel" connection) Modular 3-Phase UPS Systems have a distinct advantage over similar competitors' models. Communication between the two Tripp Lite UPSs requires only a simple plug-in cable connection. It does not require the purchase and installation of additional parallel communication cabinets, like some competitors require.