This mode incorporates relays that bypass double conversion operations during normal steady state operation.
This bypass is feeding power directly from the utility feed enabling higher efficiencies greater that 97%.
Not only does this save on power utility costs but also on the cooling required in tight spaces as the unit emits less heat losses.
The lower heat also leads to longer life of key components such as batteries.
If the quality of the power drops outside of configurable ranges, the UPS will immediately switch into On-Line mode. The switchover can take up to 10 ms.
Note that the load is susceptible to surges during the switchover period. Customers must decide if the risk to their application is worth the 4% efficiency gain.