In summary, Tripp Lite's comprehensive line of 3-Phase UPS Systems provide mission-critical equipment with the highest level of power protection. Modularity has a variety of definitions across the industry. Some manufacturers equate modularity with multiple components--if a product has more than two parts, it must be modular. Tripp Lite's definition, however, is more firmly rooted in basic customer needs for continuous availability. Tripp Lite's Modular E3 Series, 3-Phase UPS Systems feature multiple 20 KVA power modules that help ensure continuous availability by providing failsafe redundancy (if one module is removed for maintenance, the others will support the load). Redundancy is simply a backup. Network managers deploy redundant servers to ensure continuous data availability. The UPS system can help ensure continuous availability by including redundant (or "extra") components within its chassis. The most vital component in a 3-phase UPS is its power module. 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. THDi (Total Harmonic Distortion - input) is distortion generated by a UPS System that is "reflected" back through the input to the utility or generator source. Efficiency is how well the UPS system converts input into output. The higher the efficiency, the more the UPS system will save in operation costs.