UPS ECO mode, also known as 'Economy mode' or 'green mode', is an energy-saving UPS operating mode. In ECO-mode the UPS inverter operates in a "standby" mode to achieve higher efficency.  If the power fails or a problem is detected, the inverter is engaged. 

Why Eco mode? What is the benefit of Eco-mode？ 

The main benefit of ECO mode is the increased efficiency of the line, which typically runs at 98-99% compared to standard online UPS efficiency of 93-97%.  Here is a example: for a large capacity UPS with 93% efficiency，93% of the original power is powering your load, while 7% is being lost to operate the UPS. In UPS Eco-mode the efficency can be up to 98%，saving 5% power consumption.  It is a significant saving for large-scale facilities.

What is the risk of Eco-mode？ 

In online mode, the UPS continuously regenerates the output voltage. In eco-mode the load is normally powered by the bypass path, allowing raw mains power to supply the load. It is similar to the basic operating mode of an offline UPS, where the inverter is on standby and ready to switch on if there's a power problem. 

ECO mode is only recommended on sites where the utility supply is relatively stable and the load generates low harmonics so isn’t sensitive to any mains interference.