ECO mode provides the highest efficiency, but its benefits are most significant at medium to high loads. At very low load levels, the fixed power consumption of the UPS's control and bypass circuits can negate the efficiency gains. Furthermore, in normal double-conversion mode, the UPS provides better power conditioning. For the UPS5000-H, Huawei recommends against using ECO mode when the load is below 20% to ensure both optimal performance and meaningful energy savings.

A. The threshold is higher than 10%; using ECO mode between 10% and 20% load is still not recommended.

B. 30% is a safe load level for ECO mode; the recommendation applies to loads lower than this.

C. The threshold is significantly higher than 5%. Operating at such a low load in any mode is generally inefficient.

1. Huawei UPS5000-H-(300 kVA-1200 kVA) V100R001C00 User Manual, Section 5.4.1.1, "Setting ECO Mode". A note in this section explicitly states: "If the load rate is lower than 20%, you are not advised to enable the ECO mode."